Human OriginsAre we hybrids?

Retirado de http://www.macroevolution.net/human-origins.html#.UhOiDby5fMx

(acesso em 20/08/2013)

BY EUGENE M. MCCARTHY, PHD GENETICS — This article is a little different from others on

this site, because it's about the findings of my own research. I'm a geneticist whose

work focuses on hybrids and, particularly, the role of hybridization in the

evolutionary process. Here, I report certain facts, which seem to indicate that

human origins can be traced to hybridization, specifically to hybridization involving

the chimpanzee (but not the kind of hybridization you might suppose!). You can

access detailed and documented discussions supporting this claim from links on this

page. But I'll summarize the basic reasoning here, without a lot of citations and

footnotes. (If you would like to read an even briefer summary, click here; read about

some objections to the theory here; also, a recent news story)

Rationale

So why do I think humans are hybrids? Well, first of all, I've had a different

experience from most people. I've spent most of my life (the last thirty years)

studying hybrids, particularly avian and mammalian hybrids. I've read thousands,

really tens of thousands, of reports describing them. And this experience has

Chimpanzee (Pan troglodytes)

"The scientist has a lot of experience with ignorance and doubt and uncertainty, and this experience is of very great importance, I think. When a scientist doesn’t know the answer to a problem, he is ignorant. When he has a hunch as to what the result is, he is uncertain. And when he is pretty darn sure of what the result is going to be, he is in some doubt. We have found it of paramount importance that in order to progress we must recognize the ignorance and leave room for doubt. Scientific knowledge is a body of statements of varying degrees of certainty — some most unsure, some nearly sure, none absolutely certain."

— Richard Feynman

dispelled some mistaken ideas I once had about hybrids, notions that I think many

other people continue to take for granted.

For example, one widespread, but erroneous, belief is

that all hybrids are sterile. This idea keeps a lot of

people from even considering the possibility that

humans might be of hybrid origin. This assertion is

absolutely false — though I have in fact heard lots of

people make it. For instance, in reviewing the reports I

collected for my book on hybridization in birds

(Handbook of Avian Hybrids of the World, Oxford

University Press, 2006), which documents some 4,000

different kinds of hybrid crosses among birds, I found

that those crosses producing partially fertile hybrids are

about eight times as common as crosses known to

produce sterile ones. The usual result is a reduction in

fertility, not absolute sterility. My current work

documenting hybridization among mammals shows that

partially fertile natural hybrids are common, too, in Class Mammalia. And yet, it

seems most people base their ideas of hybrids on the common mule (horse x ass),

which is an exceptionally sterile hybrid, and not at all representative of hybrids as a

whole.

I should, perhaps, also mention that

differences in parental chromosome

counts, even rather large ones, do not

preclude the production of fertile hybrids.

While differences of this sort do bode ill

for the fertility of the resulting progeny,

it is only a rule of thumb. For example,

female geeps, the products of

hybridization between sheep (2n=54)

and goats (2n=60), can produce

offspring in backcrosses. Likewise,

female zeedonks (Burchell's Zebra,

2n=44 x Ass, 2n=62) have also been

fertile in backcrosses. There are many

other examples of this sort among

mammalian hybrids. Therefore, such differences between the parents in a cross do

not in any way guarantee an absolute sterility in the hybrid offspring. (For those

readers who do not know, backcross hybrids are produced when hybrids from a first

cross mate with either of the two types of parents that produced them. When the

resulting progeny mate again with the same parental type, the result is the second

backcross generation, and so forth.)

From a discussion of mules elsewhere on this website:

Zirkle (1935, p. 7) says that the sterility of the mule made it the first animal whose hybrid origin was generally recognized because “the origin of fertile hybrids could easily be forgotten, particularly the origin of those which appeared before the dawn of history.” The mule, however, was so sterile that it was necessary to produce it with the original cross (Zirkle provides extensive information on the early history of mule). The fact that the hybrid origin of the mule has so long been known, together with its marked sterility, has no doubt greatly contributed to the widespread, but erroneous belief that all hybrids are sterile. Read more about mules >>

By the same author: Handbook of Avian Hybrids (Oxford Univ. Press, 2006) attempts to list all known bird hybrid crosses. More information

A second so-called fact, which might make it seem impossible for humans to have

had a hybrid origin, is the equally erroneous notion that hybrids, especially

successful hybrids, do not occur in a state of nature. A third is the mistaken idea

that only plants hybridize, and never animals. In fact, however, natural, viable,

fertile animal hybrids are abundant. A wide variety of such hybrids occur on an

ongoing basis (read a detailed discussion documenting these facts). For example, of

the 5,000 different types of hybrid crosses listed in my book on hybridization in

birds, approximately half are known to occur in a natural setting (download a

PowerPoint presentation summarizing data on hybridization in birds). My current

research indicates a comparable rate for mammals.

Sequence data. And I must now emphasize a fact that I, as a geneticist, find

somewhat disappointing: With nucleotide sequence data, it can be very difficult to

identify later-generation backcross hybrids derived from several repeated

generations of backcrossing (for a full explanation of this fact, see the green sidebar

at far right). Instead, as is the case with other later-generation backcross hybrids,

the most revealing data is of an anatomical and/or physiological nature. And this is

exactly the kind of hybrid that it looks like we are -- that is, it appears that humans

are the result of multiple generations of backcrossing to the chimpanzee.

Human infertility. Another observation that appears significant in connection with

the hypothesis under consideration is that it has been well known for decades that

human sperm is abnormal in comparison with that of the typical mammal. Human

spermatozoa are not of one uniform type as in the vast majority of all other types of

animals. Moreover, human sperm is not merely abnormal in appearance — a high

percentage of human spermatozoa are actually dysfunctional. These and other facts

demonstrate that human fertility is low in comparison with that of other mammals

(for detailed documentation of this fact see the article Evidence of Human

Infertility). Infertility and sperm abnormalities are characteristic of hybrids. So this

finding suggests that it's reasonable to suppose, at least for the sake of argument,

that humans might be of hybrid origin. It is also consistent with the idea that the

hybridization in question was between two rather distinct and genetically

incompatible types of animals, that is, it

was a distant cross.

Methodology. The chimpanzee is

plausible in the role of one of the parents

that crossed to produce the human race

because they are generally recognized

as being closest to humans in terms of

their genetics (here, I use the term

chimpanzee loosely to refer to either the

common chimpanzee or to the bonobo,

also known as the pygmy chimpanzee;

the specific roles of these two rather

similar apes within the context of the present hypothesis will be explained in a

A personal endorsement:

"As a clinician and scientist with medical training it is a joy to find a theory so carefully and elegantly presented. My interest in the hybrid nature of modern man led me to Eugene McCarthy's website and lifework. What a revelation! Surprising and shocking. Such is the nature of truth sometimes. Life will never be seen in the same way after reading this work."

Dr Chris MillarBallarat, Victoria, Australia

subsequent section). But then the question arises: If an ancient cross between the

chimpanzee and some parental form "X" produced the first humans, then what was

that parent? Does it still exist? What was it like?

As the reader might imagine, if the assumption is correct that one of our parents is

the chimpanzee, then it should be possible actually to identify the other parent as

well. A hybrid combines traits otherwise seen only separately in the two parental

forms from which it is derived, and it is typically intermediate to those parents with

respect to a wide range of characters. Naturalists routinely use these facts to

identify the parents of hybrids of unknown origin, even backcross hybrids.

First they posit a particular type of organism as similar to the putative hybrid (in the

present case, this organism is the chimpanzee). They then list traits distinguishing

the hybrid from the hypothesized parent,

and this list of distinguishing traits will

describe the second parent. A detailed

analysis of such a triad will often

establish the parentage of the hybrid. The traits in question in such studies are

generally anatomical, not genetic. DNA evidence is used in only a very small

percentage of such identifications (and even then, rarely in efforts to identify

backcross hybrids), and yet firm conclusions can generally be reached.

So in the specific case of humans, if the two assumptions made thus far are correct

(i.e., (1) that humans actually are hybrids, and (2) that the chimpanzee actually is

one of our two parents), then a list of traits distinguishing human beings from

chimpanzees should describe the other parent involved in the cross. And by

applying this sort of methodology, I have in fact succeeded in narrowing things

down to a particular candidate. That is, I looked up every human distinction that I

could find and, so long as it was cited by an expert (physical anthropologist,

anatomist, etc), I put it on a list. And that list, which includes many, many traits (see

the lengthy table on the right-hand side of the next page), consistently describes a

particular animal. Keep reading and I'll explain.

And why might one suppose that humans are backcross hybrids of the sort just

described? Well, the most obvious reason is that humans are highly similar to

chimpanzees at the genetic level, closer than they are to any other animal. If we

were descended from F ₁ hybrids without any backcrossing we would be about

halfway, genetically speaking, between chimpanzees and whatever organism was

the other parent. But we're not. Genetically, we're close to chimpanzees, and yet

we have many physical traits that distinguish us from chimpanzees. This exactly fits

the backcross hypothesis.

Moreover, in mammalian hybrid crosses, the male hybrids are usually more sterile

than are the females. In a commercial context, this fact means that livestock

breeders typically backcross F₁ hybrids of the fertile sex back to one parent or the

other. They do not, as a rule, produce new breeds by breeding the first cross

hybrids among themselves. Often, even after a backcross, only the females are

A reader's comment:

"Hi, I'm stunned, amazed, and converted."

fertile among the resulting hybrids. So repeated backcrossing is typical. Commonly

there are two or more generations of backcrossing before fertile hybrids of both

sexes are obtained and the new breed can be maintained via matings among the

hybrids themselves. More backcrossing tends to be necessary in cases where the

parents participating in the original cross are more distantly related.

Traits distinguishing humans from

other primates

Many characteristics that clearly distinguish

humans from chimps have been noted by

various authorities over the years. The task

of preliminarily identifying a likely pair of

parents, then, is straightforward: Make a list

of all such characteristics and then see if it

describes a particular animal. One fact,

however, suggests the need for an open

mind: as it turns out, many features that

distinguish humans from chimpanzees also

distinguish them from all other primates.

Features found in human beings, but not in other primates, cannot be accounted for

by hybridization of a primate with some other primate. If hybridization is to explain

such features, the cross will have to be between a chimpanzee and a nonprimate —

an unusual, distant cross to create an unusual creature.

The fact that even modern-day humans are relatively infertile may be significant in

this connection. If a hybrid population does not die out altogether, it will tend to

improve in fertility with each passing generation under the pressure of natural

selection. Fossils indicate that we have had at least 200,000 years to recover our

fertility since the time that the first modern humans (Homo sapiens) appeared. The

earliest creatures generally recognized as human ancestors (Ardipithecus, Orrorin)

date to about six million years ago. So our fertility has had a very long time to

improve. If we have been recovering for thousands of generations and still show

obvious symptoms of sterility (see previous section), then our earliest human

ancestors, if they were hybrids, must have suffered from an infertility that was quite

severe. This line of reasoning, too, suggests that the chimpanzee might have

produced Homo sapiens by crossing with a genetically incompatible mate, possibly

even one outside the primate order.

For the present, I ask the reader to reserve judgment concerning the plausibility of

such a cross. I'm an expert on hybrids and I can assure you that our understanding

of hybridization at the molecular level is still far too vague to rule out the idea of a

chimpanzee crossing with a nonprimate. Anyone who speaks with certainty on this

point speaks from prejudice, not knowledge. No systematic attempts to cross

distantly related mammals have been reported. However, in the only animal class

(Pisces) where distant crosses have been investigated scientifically, the results have

A reader's comment: "Your conjecture is not unlike trying to reverse engineer a human being. Logically it all makes a good argument, down to the detailed level you've taken it to. I imagine that working with hybrids you HAVE to do that - even in cases where you may not think so. Logically your arguments make a lot of sense. And the corollaries and ramifications all seem to come true. I am impressed, frankly."

Stephen GarciaMechanical Design EngineerGuanajuato, Mexico

been surprisingly successful (399.6, 399.7, 399.8). In fact, there seems to be

absolutely nothing to support the idea that interordinal crosses (such as a cross

between a primate and a nonprimate) are impossible, except what Thomas Huxley

termed "the general and natural belief that deliberate and reiterated assertions

must have some foundation." Besides, to deny that interordinal mammalian crosses

are possible would be to draw, at the outset of our investigation, a definite

conclusion concerning the very hypothesis that we have chosen to investigate.

Obviously, if humans were the product of such a cross, then such crosses would, in

fact, be possible. We cannot tell, simply by supposing, whether such a thing is

possible — we have to look at data.

The Other Parent

Let's begin, then, by considering the list in the sidebar at right, which is a

condensed list of traits distinguishing humans from chimpanzees — and all other

nonhuman primates. Take the time to read this list and to consider what creature —

of any kind — it might describe. Most of the items listed are of such an obscure

nature that the reader might be hard pressed to say what animal might have them

(only a specialist would be familiar with many of the terms listed, but all the

necessary jargon will be defined and explained). For example, consider

multipyramidal kidneys. It's a fact that humans have this trait, and that

chimpanzees and other primates do not, but the average person on the street

would probably have no idea what animals do have this feature.

Looking at a subset of the listed traits, however, it's clear that the other parent in

this hypothetical cross that produced the first human would be an intelligent animal

with a protrusive, cartilaginous nose, a thick layer of subcutaneous fat, short digits,

and a naked skin. It would be terrestrial, not arboreal, and adaptable to a wide

range of foods and environments. These traits may bring a particular creature to

mind. In fact, a particular nonprimate does have, not only each of the few traits just

mentioned, but every one of the many traits listed in th sidebar. Ask yourself: Is it

likely that an animal unrelated to humans would possess so many of the "human"

characteristics that distinguish us from primates? That is, could it be a mere

coincidence? It's only my opinion, but I don't think so.

Of course, it must be admitted that two human traits do, at first, seem to pose a

contradiction. The animal in question lacks a large brain and it is not bipedal. An

analysis of the relevant anatomy, however, reveals that these two human features

can be understood as synergistic (or heterotic) effects, resulting from the

combination (in humans) of certain traits previously found only separately, in the

two posited parent forms. (The origins of human bipedality is explained in terms of

the the hybrid hypothesis in a subsequent section. Another section offers an

explanation of the factors underlying human brain expansion and, therefore,

accounts not only for the large size of the human brain itself, but also for certain

distinctive features of the human skull that are, themselves, obvious consequences

of brain expansion).

Nevertheless, even initially, these two flies in the theoretical ointment fail to

obscure the remarkable fact that a single nonprimate has all of the simple, non-

synergistic traits distinguishing humans from their primate kin. Such a finding is

strongly consistent with the hypothesis that this particular animal once hybridized

with the chimpanzee to produce the first humans. In a very simple manner, this

assumption immediately accounts for a large number of facts that otherwise appear

to be entirely unrelated.

What is this other animal

that has all these traits? The

answer is Sus scrofa, the

ordinary pig. What are we to

think of this fact? If we

conclude that pigs did in

fact cross with apes to

produce the human race,

then an avalanche of old

ideas must crash to the

earth. But, of course, the

usual response to any new

perspective is "That can't be

right, because I don't

already believe it." This is

the very response that

many people had when

Darwin first proposed that

humans might be

descended from apes, an

idea that was perceived as

ridiculous, or even as subversive and dangerous. And yet, today this exact

viewpoint is widely entertained. Its wide acceptance can be attributed primarily to

the established fact that humans hold many traits in common with primates. That's

what made it convincing. But perhaps Darwin told only half the story. We believe

that humans are related to chimpanzees because humans share so many traits with

chimpanzees. Is it not rational then also, if pigs have all the traits that distinguish

humans from other primates, to suppose that humans are also related to pigs? Let

us take it as our hypothesis, then, that humans are the product of ancient

hybridization between pig and chimpanzee. Given the facts presented in the

discussion of stabilization theory on this website, it seems highly likely that humans

are hybrids of some kind. This particular hypothesis concerning the nature of our

parentage is, as we shall see, a fruitful one. For the present there's no need to make

a definite decision on the matter, but certain lines of reasoning do suggest the idea

should be taken seriously:

From a recent Twitter conversation with a biologist who says he's convinced by the argument presented in the Hybrid Hypothesis:

First of all, the notion is set forward

strictly as a hypothesis. No claim whatever

is made that it is actually a fact that

humans somehow arose through

hybridization of pigs with chimpanzees. In

contrast, proponents of the idea that

humans are closely related to apes (and

not to pigs) often speak as if their case

has been proved beyond doubt. But, of

course, it has not. The wide acceptance of

this idea may actually be due to the lack

of any competitive theory. I merely

propose an evaluation of two distinct

hypotheses by the usual scientific

criterion: The hypothesis less consistent

with available data should be rejected.

Even if we could identify some

objective unit of measure for "distance" or

"similarity" (which is not at all a

straightforward problem), we would still

expect some crosses to be more distant

than others — that is, the various types of

possible crosses would constitute a

continuum. Many would be "close" and

some would be "distant." But we would

expect at least a rare few to be very

distant. While these few might be rare,

they might be among the most interesting,

because they would offer an opportunity

to obtain something radically different.

Perhaps, it is only a subjective bias, but I

believe that a human being, when taken

as a whole, is radically different from a

chimpanzee.

On the other hand, if we first

compare humans with nonmammals or

invertebrates (e.g, crocodile, bullfrog,

octopus, dragonfly, starfish), then pigs and

chimpanzees suddenly seem quite similar

to humans. Relative impressions of "close"

and "far" are subjective and depend on

context.

Pigs and chimpanzees differ in

chromosome counts. The opinion is often

expressed that when two animals differ in

A reader's comment: "Wow! I learned of this site and your pig-chimpanzee-hybrid paper only a few hours ago, and have been stuck here ever since. Fantastic work...Anyway, I look forward to reading more. I know you call this only a hypothesis and not yet a theory, but it sure calls for some 'splainin'. Thanks!"

—Edward FalkowskiBoulder, Colorado, USA

My response to a reader who recently wrote in to say that the only convincing evidence for this theory would be sequence data: I'm not saying pig DNA in the human genome "would not" be detectable. That's putting words in my mouth. I'm saying "might not." Or, better, "could easily have been missed without this guiding hypothesis." You seem to somehow be assuming that it isn't there. As far as I'm concerned, maybe it is, maybe it isn't. But if it is, obviously, it's not obvious. As to sequence data, in my opinion, your view of what constitutes evidence needs to be widened. It seems a bit much to insist that the only thing that can convince anyone of anything is sequence evidence. If that's true, then law courts will have to throw out all the murder weapons, eyewitness testimony, alibis and everything else, and focus instead on DNA evidence alone, because DNA, if what you're saying is true, is the only evidence that has any meaning. But you know that's not right. And I think you therefore have to admit that you're showing a certain bias here. Besides, I'm not making a strong statement. I'm only saying that, given the likely circumstances (an initial cross between chimpanzee and pig, followed by several generations of backcrossing to chimpanzee), analyzing the genetic data and reaching any strong conclusions is likely to be a pain. Maybe there is something there that can be found, but whatever it is, I think it will require lots of money and a team of well-equipped scientists to locate. And think about this: if sequence data is so great, what exactly has it told us about the basis of the many differences between a human and a chimpanzee? I'll tell you: zero! Nothing whatsoever. Whereas the theory that I propose clearly explains virtually every one of those differences. So forgive me if I don't race to embrace the sequence approach to understanding the origin of the distinctive features that make us human. So far as I can tell, sequence analysis has been absolutely uninformative on that front.

this way, they cannot produce fertile hybrids. This rule is, however, only a

generalization. While such differences do tend to have an adverse effect on the

fertility of hybrid offspring, it is also true that many different types of crosses in

which the parents differ in chromosome counts produce hybrids that capable

themselves of producing offspring.

There have been no systematic, scientific surveys of the crossability of

mammals belonging to different taxonomic orders (a cross between pig and

chimpanzee would be interordinal). Any firm opinion on such a point must

therefore, necessarily, be prejudiced. In fact, certain fishes belonging to different

orders have been successfully crossed, and available information on mammalian

hybrids indicates that very distant crosses among mammals, too, have occurred.

For example, evidence published in the journal Nature demonstrates that the

platypus genome contains both bird and mammal chromosomes (223.2). As Franz

Grützner, the lead author of the study, stated in a related news story, "The

platypus actually links the bird sex chromosome system with the mammalian sex

chromosome systems." How could this be the case if a bird and a mammal did

not at some time in the past hybridize to produce a fertile hybrid? Such a cross

would, of course, be even more distant than one between a chimpanzee and a

pig. And seemingly, a cross between a primate and a pig did occur only a few

years ago, in 2008.

Ultimately, the interaction of gametes at the time of fertilization, and the

subsequent interplay of genes (derived from two different types of parents)

during the course of a hybrid’s development cannot be predicted by any known

laws because the interaction is between a multitude of extremely complex

chemical entities that each have an effect on others. It is for this reason that the

degree of similarity perceived between two organisms is no sure indicator of their

crossability.

Another suggestive fact, probably known to the reader, is the frequent use of

pigs in the surgical treatment of human beings. Pig heart valves are used to

replace those of human coronary patients. Pig skin is used in the treatment of

human burn victims. Serious efforts are now underway to transplant kidneys and

other organs from pigs into human beings. Why are pigs suited for such

purposes? Why not goats, dogs, or bears — animals that, in terms of taxonomic

classification, are no more distantly related to human beings than pigs? (In

subsequent sections, these issues are considered in detail.)

God did not place pigs and humans in different taxonomic orders.

Taxonomists did. A great deal of evidence (read a discussion of this topic) exists

to suggest that taxonomists are, in no way, infallible. Our ideas concerning the

proper categorization of animals are shaped by bias and tradition to such an

extent that it would be rash to reject, solely on taxonomic grounds, the feasibility

of such a cross.

The general examination of the process of evolution as a whole (as

presented elsewhere on this site) strongly suggests that most forms of life are of

hybrid origin. Why should humans be any different?

It might seem unlikely that a pig and a chimpanzee would chose to mate, but

their behavior patterns and reproductive anatomy do, in fact, make them

compatible (this topic is considered in detail in a subsequent section). It is, of

course, a well-established fact that animals sometimes attempt to mate with

individuals that are unlike themselves, even in a natural setting, and that many of

these crosses successfully produce hybrid offspring.

Accepted theory, which assumes that humans have been gradually shaped

by natural selection for traits favorable to reproduction, does not begin to account

for the relative infertility of human beings in comparison with nonhuman primates

and other types of animals (see previous section). How would natural selection

ever produce abnormal, dysfunctional spermatozoa? On the other hand, the idea

that humans are descended from a hybrid cross — especially a relatively distant

cross — provides a clear explanation for Homo's puzzling and persistent fertility

problems.

If we supposed standard theory to be correct, it would seem most peculiar

that pigs and humans share features that distinguish human beings from

chimpanzees, but that pigs and chimpanzees should not. Conventional theory

(which assumes that pigs are equally as far removed from humans as from

chimpanzees) says that pigs and chimpanzees would share about as many such

traits as would pigs and humans. And yet, I have never been able to identify any

such trait—despite assiduous investigation. The actual finding is that traits

distinguishing chimpanzees from humans consistently link pigs with humans

alone. It will be difficult to account in terms of natural selection for this fact. For

each such feature, we will have to come up with a separate ad hoc argument,

explaining how the feature has helped both pigs and humans to survive and

reproduce. On the other hand, a single, simple assumption (that modern humans,

or earlier hominids that gave rise to modern humans, arose from a cross between

pig and chimpanzee) will account for all of these features at a single stroke.

For my own part, curiosity has carried me away from my old idea of reality. I no

longer know what to believe. Is it possible that so many biologists might be wrong

about the nature of human origins? Is it

possible for a pig to hybridize with a

chimpanzee? I have no way of knowing at

present, but I have no logical or evidential

basis for rejecting the idea. Before

dismissing such a notion, I would want to be

sure on some logical, evidentiary basis that I

actually should dismiss it. The ramifications

of any misconception on this point seem

immense. As Huxley put it long ago, "The

question of questions for mankind — the

problem which underlies all others, and is

more deeply interesting than any other —is the ascertainment of the place which

Man occupies in nature."

A reader's comment: "The theory overcomes the creationist's objection to gradualism and the evidence for pig ape hybridity has no stronger scientific competition. Open your mind and look at the facts. Consider how it might be true. Let go of your prejudices and misinformations. Not all hybrids are sterile. Examples of hybrid crosses are common in nature, including fertile ones. Admittedly transordinal crosses are unusual, but then we are extraordinary."

Are we simply another type of primate, like the chimpanzee or the baboon? Or are

we a complex melange, an alloy of two very distinct forms of life? These are

questions that can only be resolved by examining the evidence. I invite the reader

to consider these two possibilities as simple hypotheses, to consider the data coldly,

and then to determine which of the two is more consistent with available evidence.

Some of the most easily accessible evidence that can be used to evaluate the

hybrid hypothesis is visible in the mirror. In this section, we will consider certain

external features that link humans with pigs. Much of my research on pigs has

centered on the ordinary pig (Sus scrofa). Of course, ordinary pig is really a catchall

term for a variety of breeds. "There are currently some 87 breeds of domestic pigs

in the world, most of them in Europe and North America," according to Pond and

Houpt, and "another 225 or more groups of pigs not recognized as breeds but each

having unique characteristics, appearance, or geographical location."1 However, the

focus here will be on traits that are generally characteristic of Sus scrofa.

And now, let's look a little more closely at some human distinctions that, as it turns

out, are characteristics of pigs as well. Traits that distinguish us from chimpanzees

and other primates are the only ones that will be discussed, because traits that

humans share with primates have no bearing on the question of whether humans

are of hybrid origin. Under the hypothesis being considered, it would make no

difference if humans are more similar to chimpanzees in most respects than to pigs.

The interesting finding is that those features that do distinguish humans from

chimpanzees and other primates can be consistently accounted for by reference to

the pig.

This physical affinity of humans and pigs is easily observable in certain external

features. This fact did not escape Thomas Mann, who once wrote "The pig with its

little blue eyes, its eyelashes and its skin has more human qualities than any

chimpanzee — think how often naked human beings remind us of swine."² Although

I do not concur in Mann's assertion that pigs share more traits with humans than do

chimpanzees, I do think pigs and humans share more than enough traits to suggest

a relationship. For example, lightly pigmented eyes, in shades of blue, green, and

tan, are never found in chimpanzees or orangutans.3 There is, apparently, only one

known case of a gorilla with blue eyes.4 Light-colored eyes are also rare in other

primates.5 Why, then, are they common in certain human populations? Where did

this trait come from? One conceivable explanation is that it was inherited from blue-

eyed pigs. Blue is a common eye coloration in swine (as are green, yellow, and tan).

The dark pigment (melanin), found so consistently in the irises of nonhuman

primates, is beneficial. It absorbs ultraviolet light. To protect their eyes from these

damaging rays, pigs depend on their narrowly slit, heavily lashed eyelids. Humans

shield their eyes in a similar way, unlike the typical wide-eyed, sparsely lashed ape.

[A reader, by the name of Chase Dumont, wrote in with the following comment,

which is of interest in the present context: "The outer appearance of the eye itself

looks quite different from a chimpanzee's and more like a pig's — the pupil/iris in a

chimpanzee eye covers the entire eye, while

the pupil/iris in a pig eye occupy a much

smaller footprint, displaying much of the

'white' of the eye — as in humans)."]

Neither is it clear how a protrusive

cartilaginous nose might have aided early

humans in their "savannah hunter lifestyle."

As Morris remarks, "It is interesting to note

that the protuberant, fleshy nose of our

species is another unique feature that the

anatomists cannot explain."6 This feature is

neither characteristic of apes, nor even of

other catarrhines.7 Obviously, pigs have a

nose even more protuberant than our own.

In a pig's snout, the nasal wings and septum

are cartilaginous as ours are.8 In contrast, a

chimpanzee's nose "is small, flat, and has no

lateral cartilages" (Sonntag9). A cartilaginous

nose is apparently a rare trait in mammals.

Primatologist Jeffrey Schwartz goes so far as

to say that "it is the enlarged nasal wing

cartilage that makes the human nose what it

is, and which distinguishes humans from all

other animals."10 The cartilaginous structure

of the pig's snout is generally considered to be an "adaptation" for digging with the

nose (rooting). Rooting is, apparently, a behavior pattern peculiar to pigs. Other

animals dig with their feet.

A protruding nose is perhaps the most prominent difference between a human face

and that of a chimpanzee, but discussions of human evolution rarely mention the

nose, perhaps because its lack of utility precludes explanation in terms of

adaptation. Instead, most analyses deal with the fleshless skull, where the

protrusiveness of the human nose is a bit less obvious (but visible nonetheless). It is

a peculiar omission, because useless (nonadaptive) traits are widely considered to

be the best indicators of relationship. What is the evolutionary utility of our unique

nasal structure? Is it functional? Or is it the

genetic residue of an ancient hybrid cross?

Another feature to consider is the philtrum,

the dent seen on the center of the human

upper lip. Apes lack this typical human

feature.11 It seems a useless structure from

a survival standpoint. Why is it seen, then,

the world over in Homo? In both human

beings and pigs, during the early stages of

In the gorilla, Schultz remarks that he "found a roof cartilage of less than 1 cm² and paper-thin alar cartilages, limited to the nasal center and not extending into the huge wings, which were mere pads of fat. In contrast to this, the prominent nose of man is far more extensively supported by cartilage, which closely determines its shape. While the nearly immobile nasal wings of apes consist of little more than skin and fat, the thin and mobile wings of human noses are extensively stiffened by cartilage to keep them from being sucked shut with every inhalation (495.9,52).

While Schwartz's statement concerning the uniqueness of the human nose is generally correct, it must be said that certain Asian monkeys (Nasalis, Rhinopithecus) do have protrusive noses (235.4,29).

Walker (588.4,1175) states that "this cartilaginous snout [of pigs], used for turning up surface soil, is strengthened by an unusual bone, the prenasal, situated below the tip of the nasal bones of the skull." Composed primarily of cartilage, this flexible prenasal "bone" finds its equivalent in the cartilaginous tip of the human septum.

Specifically, Sonntag notes the lack of a philtrum in chimpanzees (533.6,371).

development, the upper lip is cleft, though I have not been able to find any

evidence of such a cleft in the embryos of any nonhuman primate. As development

continues, this cleft usually closes in humans, but persists in pigs.12 The human

philtrum is a visible residue of this primordial split lip. In those human beings where

this split never closes, the condition is known as cleft lip, a common birth defect.

The frequent occurrence of cleft lip in humans is hard to explain if it is assumed that

we are closely related only to primates. If the assumption, however, is that human

beings are derived from a pig-chimpanzee cross, this finding becomes far more

understandable.

Similar thinking explains the shortness of the human upper lip (distance between

mouth opening and nostrils). Why has our upper lip become shorter and thicker in

the course of evolution? All apes have upper lips much longer than those of

humans,13but a pig's upper lip is so short that it is scarcely more than an appendage

of the snout.14 Morris15 makes much of the fact that human lips are covered on their

exterior surface by glabrous (i.e., absolutely hairless) mucous membrane:

Like the earlobes and the protruding nose, the lips of our species are a unique feature, not found elsewhere in the primates. Of course, all primates have lips, but not turned inside-out like ours. A chimpanzee can protrude and turn back its lips in an exaggerated pout, exposing as it does so the mucous membrane that normally lies concealed inside the mouth. But the lips are only briefly held in this posture before the animal reverts to its normal 'thin-lipped' face. We on the other hand, have permanently everted, rolled-back lips.

He goes on to suggest that our peculiar lips are the product of "sexual selection."

But other explanations are conceivable: In describing the skin of pigs, Getty16 states

that "there are no true glabrous surfaces other than the labial borders," which are

composed of red mucous membrane.

In reference to human earlobes, Morris

observes that "anatomists have often

referred to them as meaningless

appendages, or `useless fatty excrescences.'

By some they are explained away as

`remnants' of the time when we had big

ears. But if we look to other primate species

we find that they do not possess fleshy

earlobes. It seems that, far from being a remnant, they are something new."17

Perhaps, however, they are really something old on a new face. Sisson describes

the lower portion of a pig's ear as "strongly

convex below, forming a prominence

somewhat analogous to the lobule of the

human ear."18

An additional feature of the human ear

should be mentioned here, the Darwinian

Some disagreement exists in the literature over the question whether earlobes are present in apes. Sonntag says they are not seen in the chimpanzee (533.8,86), but Schultz (495.65,146) claims they are sometimes found in the African apes and even in certain monkeys.

A reader's comment: "My soon-to-be-eight year old is in fact telling everyone he meets now, matter of factly as if it was today's weather, 'People are chimp pigs!' Doesn't phase him in the least. He's quite proud of it."

—Gary Lawrence Murphy Owen Sound, Ontario, Canada

tubercle (see Darwin's illustration below). In his Descent of Man, Darwin comments

on this feature sometimes found on the rim of human ears which he describes as "a

little blunt point, projecting from the inwardly-folded margin, or helix … These

points not only project inward, but often a little outward, so that they are visible

when the head is viewed from directly in front or behind. They are variable in size

and somewhat in position,

standing either a little higher or lower; and they sometimes occur in one ear and not on the other. Now the meaning of these projections is not, I think, doubtful, but it may be thought that they offer too trifling a character to be worth notice. This thought, however, is as false as it is natural. Every character, however slight, must be the result of some definite cause; and if it occurs in many individuals deserves consideration. The helix obviously consists of the extreme margin of the ear folded inward; and this folding appears to be in some manner connected with the whole external ear, being permanently pressed backward. In many monkeys, which do not stand high in the order, as baboons and some species of macacus, the upper portion of the ear is slightly pointed, and the margin is not at all folded inward, a slight point would necessarily project inward and probably a little outward. This could actually be observed in a specimen of the Ateles beelzebuth in the Zoological Gardens; and we may safely conclude that it is a similar structure — a vestige of formerly-pointed ears — which occasionally reappears in man.19

Darwinian tubercle(Darwin, 1871)

Primatologist Adolph Schultz (1973), however, flatly contradicts Darwin, saying that

"clearly pointed ears, commonly called `satyr ears,' are among monkeys typical for

only macaques and baboons and do not occur in any hominoids [great apes], not

even in the early stages of development. There is no justification, therefore, to

interpret the occasional `Darwinian tubercles' on human ears as an atavistic

manifestation of ancestral pointed ears."20 But Schultz has not, perhaps, taken into

consideration the pointed ears of swine.

Swine have prominent eyebrow hair. On the brows of the chimpanzee fetus it is

possible to discern a region of light-colored bumps following a pattern similar to that

of the human eyebrow. Adult apes, however,

have no eyebrow hair.21 On their eyelids,

pigs have luxuriant eyelashes, thicker even

than those of human beings. In many pigs

these cilia, as anatomists term them, are so

thick that the animal seems to be wearing

false eyelashes. But apes scarcely have

eyelashes at all, despite the apparent

survival value of this feature. Also, pongids

have prominent brow ridges while pigs and most humans do not. If we choose to

explain the development of human eyelashes and eyebrows in terms of natural

selection, we must wonder why apes, which have existed at least as long as any

hominid, have failed to acquire them. Perhaps their heavy brow ridges sufficiently

protected their eyes, but if such is the case, why did not brow ridges also suffice for

Homo? What was the pressing need that caused Homo to substitute tufts of hair for

ridges of bone?

Dermal Characteristics

That humans lack the hair cover of nonhuman primates is an accepted fact. "It is

this single factor that constitutes the chief difference between human skin and the

skin of other mammals" (Montagna22). Some writers say that the hair coat of a

chimpanzee is "sparse." But if "sparse" describes chimpanzee pelage, then "naked"

accurately describes the skin of human beings. Any human who even approached

the hairiness of other primates would be considered abnormal. Pigs, however, are a

different case. Many domestic pig breeds have skin just as naked as human skin. As

Cena et al. (101.9,521) observe, "Hair densities [of animal coats] range from the

sparse residual covering on man and the pig with 10-100 hairs per cm², to [the]

dense coats of species such as the fox and rabbit with about 4,000 per cm²." In wild

Sus scrofa, according to Haltenorth, the density of hair coverage varies from

"sparse to thick," depending on the specimen or variety in question.23 For example,

the hair of the modern day wild variety of Sus scrofa present in Sudan (S. s.

senaarensis) is quite sparse.24

Other primates do not have the long mane of hair that tops the head of an unshorn

human, nor do they have beards. Haltenorth

notes that in some varieties of Sus scrofa,

manes are found on the neck and back

("Näcken-/Rückenmähne"), beards on the

cheeks ("Wangenbart"), and shocks of hair

on the forehead and atop the head

("Stirn-/scheitelschopf"). He also says that

the last of these three traits is found, among

pigs, in Sus alone.25 A prehistoric painting of a pig found in Altamira Cave in

According to Schummer et al. (503.3,497), "The eyebrows [of the domestic pig] are formed by 2 to 3 rows of prominent tactile hairs formed at the base of the upper eyelid; there are more than 40 in all and they are up to 8 cm long. They form into bundles, especially at the medial angle of the eye."

Schultz (495.07,Plate 1) pictures a 185-day-old chimpanzee fetus that is virtually hairless except for a thick patch atop its head (in the same region it is seen in human beings). It also has eyebrow hair arranged in the same pattern as do humans.

northern Spain depicts an animal with a beard and thick hair atop its head

(pictures). Sus barbatus, an extant pig native to southeast Asia (which forms fertile

hybrids of both sexes in crosses with S. scrofa) has little hair on its body, but does

have a very thick and bushy beard.26

Panniculus adiposus. In an article on the evolution of human skin, renowned

cutaneous comparative anatomist William Montagna notes that, "Together with the

loss of a furry cover, human skin acquired a hypodermal fatty layer (panniculus

adiposus) which is considerably thicker than that found in other primates, or

mammals for that matter. This is not to say that only man has a fat skin, but a thick

fatty layer is as characteristic an attribute of human skin as it is of pig skin."27

Similarly, Dyce et al. (160.1,742) note that there is a "well developed fat deposit

present almost everywhere in the subcutis." Primatologist F. W. Jones also noted

this fat layer:

"The peculiar relation of the skin to the underlying superficial fascia is a very real distinction [of human beings], familiar to everyone who has repeatedly skinned both human subjects and any other members of the primates. The bed of subcutaneous fat adherent to the skin, so conspicuous in man, is possibly related to his apparent hair reduction; though it is difficult to see why, if no other factor is invoked, there should be such a basal difference between man and the chimpanzee."28

Panniculus carnosus. "Another particularity of human skin is its general lack, or loss,

of the cutaneous skeletal muscle layer (panniculus carnosus) found throughout the

skin of most other mammals. Remnants of a panniculus carnosus in human skin are

found at the front of the neck in the apron-like, thin platysma muscle … All other

primates, even the great apes, have a panniculus carnosus over much of the body"

(Montagna29). As in humans, the cutaneous musculature of pigs is well developed in

the neck (platysma muscle) and face, but sparse or nonexistent elsewhere.30

In animals having a panniculus carnosus, the skin receives its blood supply from

direct cutaneous arteries (large superficial vessels running parallel to the skin

surface in the cutaneous muscle sheath). But when no panniculus carnosus is

present, arteries feeding the skin rise up like little trees from deep within the body.

Arteries of this latter type are called musculocutaneous. These two forms of dermal

circulation are depicted in the illustration below. Both pig skin and human skin are

supplied by musculocutaneous arteries.31 As Daniels and Williams observed in a

1973 article on skin flap transfer, "Most experimental animals do not have a

vascular supply to the skin similar to that of man. The pig's cutaneous vascular

supply has been demonstrated anatomically and surgically to be more comparable

than most to that of man … As in man, the pig's skin is supplied by ubiquitous

musculocutaneous arteries and by a few direct cutaneous arteries."32 This

observation has been confirmed by other authors: "Except for pigs, whose

cutaneous vasculature resembles that of man, loose-skinned mammals are

vascularized by direct cutaneous arteries" (Montagna and Parakkal33). Therefore, in

this respect, human skin is more similar to pig skin than to that of nonhuman

primates: "Actually, the vascularity of the skin of most nonhuman primates is

essentially similar to that of other furred animals" (Montagna34). In particular,

Baccaredda-Boy,35as well as Moretti and Farris,36 found that the skin of chimpanzees differs from that of human beings in having numerous large, superficial vessels (i.e., direct cutaneous arteries).

Human skin also stands apart from that of

other primates — and from that of most

other mammals for that matter — with

respect to the quantity of blood that can be

circulated through it.37 A certain amount of

blood is needed just to feed the skin. This is

the amount it receives in most animals. In

humans, however, the maximum blood flow

can be more than a hundred times greater

than this minimum.38 Fed by temperature-

sensitive musculocutaneous arteries, the

densely spaced cutaneous capillaries of

human beings play an essential

thermoregulatory role.39 When the body

begins to overheat, large quantities of warm blood can be rapidly cooled in these

capillaries via sweat evaporation. One measure of cutaneous vascular density is the

capillary loop separation interval. In human beings, the typical distance between

capillaries ranges from 50 to 100 microns.40 In porcine flank skin, this figure is

reduced to only about 20 microns, a separation interval so small as to be almost

incredible. When white pigs are exposed to high temperatures, the skin flushes pink

In the paragraph at left, the calculations for the pig capillary separation interval were based on Young and Hopewell's data (605.4, Fig. 1 and Table 2). In the chimpanzee, the epidermis is richly vascularized only beneath the friction surfaces (palms and soles), not beneath the hairy-skin regions. Thus, regarding the chimpanzee, Montagna (365.5,191) states: "Where the epidermis is flat [i.e., hairy-skin regions], capillary loops are ill-defined … Capillary loops are deepest and most complicated underneath the epidermis of the friction surfaces.

with blood (even in the absence of sunlight) as it does in light-skinned human

beings under similar conditions.41

Fleas. Perhaps this difference between our

cutaneous vasculature and that of our primate

kin accounts for another human distinction:

"Ironically," writes Nicole Duplaix, "man is

unique among the primates in having fleas."42

More than 2,400 distinct types of fleas have

been treated as species or subspecies.43

Parasites are usually rather specific in their

choice of host. Fewer than twenty of these

2,400 types will readily bite human beings.44 Foremost among those that feed on

Homo sapiens is the human flea, Pulex irritans, but we are not the only suitable

hosts for this species. According to Bennett,

"Pulex irritans, the human flea, breeds freely

in hog-house litter and may become a

serious pest of swine."45

The panniculus adiposus replaces hair as an

insulating layer in human beings and pigs.

According to Beckett (63.8,2),

The pig increases or decreases the amount of heat lost … by varying the blood flow in the [skin's] capillary bed … If all blood flow to the outer body parts were stopped, the thermal resistance between the body cavity or muscle tissue and skin surface would approximately equal the resistance of the fat layer plus the resistance of the hair and skin. To the extent that a pig is able to direct a sizable flow of blood through the skin and region just below the skin, the fat layer is by-passed and thermal resistance is at a minimum.

In the figure above, notice that the musculocutaneous arteries pass through the

cutaneous fat. This perforated fat layer constitutes an insulating mechanism that

can respond quickly to ambient temperature, a characteristic that hair lacks.

Dilation of the musculocutaneous arteries in response to heat increases blood flow

to the skin. This increase in circulation can raise skin surface temperature to a level

almost as high as that within the body, thus increasing the rate at which heat is lost

to the environment.b In cool environments, constriction of these arteries reduces

skin temperature and, consequently, the rate at which body heat is lost to the

atmosphere because the fat layer can then serve as an insulating blanket.

Possession of a panniculus adiposus allows

adjustment to changes in ambient

temperature on a moment-to-moment basis

— a clear advantage in the temperate zones

where much of the human race has made its

home, because these regions are much more

Human flea, Pulex irritans

Newton's law of cooling states that the rate at which heat flows out of a warm body into a cooler surrounding medium is proportional to the difference between the temperature at the body's surface and the temperature of the surrounding medium.

Obviously, furred animals cannot remove their coats when it's hot — they shed. But shedding is a process that takes weeks, not minutes. It is a seasonal adjustment, not the moment-to-moment adjustment seen in human beings and pigs.

subject to sudden, extreme shifts in temperature than those close to the equator.

Nonhuman primates and other furred animals do not have the option of adjusting

their skin temperature. Because their skin is not insulated from the rest of the body

by a layer of fat, its temperature must remain near that of the flesh beneath it.

Pig skin is separated from the inner body by a thick fat layer, and it can cool to an

extreme degree. Fat, not hair, is the primary insulating barrier.47 Alaskan swine can

withstand sub-zero temperatures by cooling their skin to as little as 9˚ C (at an

ambient temperature of -10˚ C) without suffering tissue damage.48 Acclimatized

human beings, too, can reduce skin temperature to about 10˚ C without injury.49

This mode of insulation is completely different from that of nonhuman primates,

more like that seen in certain aquatic mammals (e.g., seal, walrus). With the

exception of the pig, it seems that no other land animal has this form of insulation.

More than a naked ape, Homo is a variably insulated naked ape. In hot

environments human beings (and pigs) can the increase circulation of warm blood

to the skin and raise temperatures almost to the level of body core temperature,

thus maximizing heat loss to the surrounding air. If weather turns cold, they can

restrict cutaneous circulation, cooling the skin to such a degree that heat loss is

significantly reduced. This ability is especially apparent in fat50or acclimatized

individuals.51 Although a cultural advance, the invention of clothing, made it

possible for Homo to inhabit cool regions formerly off-limits to primates, a biological

advance, in the form of a new insulation system, has increased the human ability to

withstand the sudden temperature variations found in those regions.

Besides being a good insulator, human skin

is surprisingly thick. "The epidermis over our

general body surface ["hairy skin" see note

at right] is substantially thicker than that of

other primates: the horny layer [stratum

corneum] can be peeled off intact as a

diaphanous but tough membrane that can

be used for experimental purposes … The

epidermis in the hairy skin on nonhuman primates, mostly like that of any other

furred mammal, is relatively thin, with a relatively thin horny layer" (Montagna52).

Pigs, though, have a thick epidermis and

stratum corneum, thicker even than that of

human beings.53

The elasticity of our skin is also unusual.

"Whereas the skin of the great apes and that

of some of the simian primates have variable

amounts of elastic fibers, in no animals,

regardless of sex, age, or locality have we

found the abundance of elastic tissue

characteristic of human skin" (Montagna54).

If skin has any hair whatsoever (scalp, forearm, belly) dermatologists refer to it as "hairy skin." Hairy skin in humans, then, is the skin covering most of the body, the general body surface. Other regions, that are absolutely hairless (lips, palms, soles) are called "glabrous."

Another quotation from Montagna (360.3,13): "Elastic fibers are numerous everywhere [in pig skin]. In the papillary layer delicate fibers branch toward the epidermis as they do in the skin of man."

In the case of the chimpanzee's dermis, Montagna and Yun state that, "Elastic fibers, nowhere numerous, are concentrated in the papillary body and in the deep portion of the reticularis dermis" (365.5,191).

This finding comes from the same author who, in an earlier article comparing

human skin with that of pigs, observed that "one of the most striking resemblances

between these two skins [pig and human] is the large content of elastic tissue in the

dermis."55

He also remarks that "the surface of both skins [human and porcine] is grooved by

intersecting lines which form characteristic geometric patterns."56 In a separate

paper on the evolution of human skin he provides a little more detail:

The outer surface of human skin is crisscrossed, almost everywhere, by fine intersecting congenital lines … (You can confirm the presence of these lines by looking at the back of your hands). This characteristic is not limited to human skin; creases are also found on the skin of pachyderms, walruses, and, to a lesser extent, pigs. With the exception of occasional, shallow creases, the surface of the hairy skin of nonhuman primates is smooth.57

The presence of these lines in both pigs and humans is not easily explained in terms

of natural selection since they have no known function.58

On the underside of our "hairy skin" (general body surface), where the epidermis

meets the dermis, is a different patterning not corresponding in its configuration to

the outside patterning described in the preceding paragraph. A similar, though

coarser, pattern is also characteristic of the epidermal-dermal junction in pigs.

Montagna, however, notes that "in split-skin preparations where the epidermis is

neatly removed from the dermis, the epidermis of heavily haired animals is flat.59

Even in monkeys and apes, epidermal grooves are found only around the

attachment of the ducts of glands and pilary canals." We can account for a finer

patterning in humans than in pigs by the fact that a fine mesh is intermediate

between the coarse patterning of pig skin and the smooth undersurface of

nonhuman primate skin.

So, in the pig, we have a sparsely haired animal with

a fatty, stretchy skin supplied by musculocutaneous

arteries. The surface of the hairy skin is marked by

congenital lines similar to those seen in human

beings, and the patterning of the epidermal-dermal

junction is also quite similar in the hairy skin

regions. Under the hypothesis that we are

considering, it makes little difference that pig skin

differs from human skin in other ways. The essential point is that, in those cases in

which our skin is peculiar for a primate, an explanation for each such anomaly can

be found in the skin of pigs.

The Savanna Hunter

Note: A section discussing sweating in humans, pigs, and chimpanzees, which formerly appeared here, has been moved. Sorry for any confusion or inconvenience this may have caused! Jump to the new location >>

Pigs sweat when they are hot. "The apocrine

[i.e., sweat] glands of the horse and pig

secrete profusely during violent exercise and

stress" (Montagna160). This sweating serves a

thermoregulatory function in pigs just as it

does in human beings.161 The hairy skin

sweat glands of nonhuman primates,

however, do not respond to thermal

stimulation. The failure of nonhuman

primates to sweat puzzled Montagna: "One

might surmise," he writes,

that, like man, these animals sweat in response to heat stimulation. However, with singular exceptions, if the glands secrete at all, the amount is so small that it cannot be recorded. Sometimes animals show beads of sweat on the facial disc when under deep anesthesia, but our efforts to induce thermal sweating have failed. We have also largely failed to induce sweating with sudorific drugs, either cholinomimetic or adrenomimetic. In the chimpanzee, very few, small sweat drops were recorded even after the administration of shockingly large doses of these drugs.162

In contrast, even a small dose of

acetylcholine or adrenaline elicits sweating

in pigs. Even the immature pigs studied by

Ingram (247.1,95) responded to adrenalin.

The notion that nakedness has somehow

enhanced sweat evaporation in humans is

widely received. Supposedly, our sparse

pelage allowed our ancestors to cool their

skin more rapidly than hairy animals in hot,

dry environments, or somehow improved

their ability to dissipate metabolic heat while

rushing about the savannah in pursuit of

prey. Russell Newman, however, points out

that our lack of reflective hair actually

increases solar heat load and the need to

sweat.164 To substantiate this claim, he cites

a study by Berman showing that cattle

exposed to the sun sweat more after their

hair is removed.165 Similarly, panting

increases in shorn sheep.166

A mature pig has about 500,000 large sweat glands distributed over its entire body (503.3,497; 506.5,316). Nevertheless, it is often asserted in the literature that pigs do not sweat. This assumption can be traced to studies by Ingram and by Mount, who studied perspiration rates in immature animals, usually sedentary piglets (247.03; 247.1; 389.7; 390.1; 390.2; 390.3; 390.5). Studies evaluating pig sweating have concentrated on young pigs because they are of greater commercial interest. Immature animals are no more appropriate for determining the evaporative qualities of a boar or a sow than a toddler would be for revealing traits of an adult human—Children sweat much less than do adults (584.4,577). Small animals have a tendency to hypothermia (because their surface area is large in proportion to their size), not hyperthermia, and have little tendency to sweat (390.8,182). Perspiration in pigs is often overlooked because these animals are, apparently, more efficient sweaters than are humans. Their sweat glands seem to be better attuned to thermoregulatory needs (they produce no more sweat than what is necessary to cool cutaneous blood by evaporation). Very little sweat is lost to runoff because sweat rarely builds up on the skin. But observed rates of sweating in mature pigs are approximately comparable to those of humans. Beckett (63.4) found that a 350 lb. sow at rest lost approximately 95 g/m² in sweat per hour at a dry bulb temperature of 98E F and wet-bulb temperature of 81). At a much higher temperature (122EF dry bulb and 79EF wet bulb), Myhre and Robinson found that 70 kg men at rest lost moisture (sweat + respiration) at a rate 250 g/m<² per hour (398.7,Table 3). Even in smaller pigs (198 lb. gilts), skin moisture loss is important (387.8,Table 1), ranging from one-third to two-thirds of total moisture loss (lung + skin). The claim that pigs need a wallow when living in hot climates (because they supposedly do not sweat) is also encountered. But Heitman and Hughes exposed hogs without access to a wallow to high temperatures (100E F; relative humidity 35%) for a week without any fatalities—conditions where the only avenue for heat dissipation is evaporative cooling (232.5,176).

Clothing, which replaces hair as a radiation barrier in human beings, has much the

same effect on human perspiration. Human beings subjected to solar heat loads

sweat more when naked than when wearing light clothing under otherwise identical

circumstances. In a study of the effects of clothing on sweat, Adolph167concluded

that "the nude man can save easily as much body water by putting on a shirt and

trousers as can the clothed man by finding good shade." Moreover, body hair does

not reduce convective heat loss "and has nothing to do with radiation of long-wave

infra-red heat to cooler objects," says Newman.168 He therefore asserts that naked

skin,

is a marked disadvantage under high radiant heat loads rather than the other way around, and that man's specialization for and great dependence on thermal sweating stems from his increased heat load in the sun.169

If increased radiant heat loads caused early

humans to depend more on sweat for

cooling, why has hair loss, which increases

those loads, progressed to the degree that it

has in Homo? Under the assumption that

humans first evolved on the arid, sun-

drenched savannah, it is difficult, in terms of

survival efficiency, to account for a reduction

in hair density that would result in increased

rates of water consumption. Newman points

out that there is no evidence that hair

interferes with sweat evaporation. Actually, I

myself performed a crude experiment, the

results of which indicate that hair actually

accelerates the evaporation of sweat. This

finding is surprising in light of evolutionary

theorists' frequent claims to the contrary.

But with a little consideration, one realizes

that a hair coat is not a vapor barrier. Fur's

ability to "breathe" has always distinguished

it from less desirable insulators that slow heat loss but don't "wick away" moisture

from the skin. Why should hair not only allow, but even enhance, evaporation rates?

There are at least two reasons. First, wet hair presents a more irregular surface to

the surrounding atmosphere than does hairless skin, augmenting the surface area

available for evaporation. Second, hair allows uniform dispersion of sweat by

capillary action, preventing the formation of the individual droplets seen on naked

skin. When such droplets form, the skin lying between them does not serve as an

evaporative surface and the vaporization rate is reduced.

My very crude experiment: I took two beakers and lined the bottom of one with a circle of rabbit fur. I then placed water, drop by drop, in equal amounts in both beakers. I continued the experiment for several days, always keeping the fur damp. Day after day, the water level rose in the beaker without fur. But no water buildup at all occurred in the other beaker.

Claims that naked skin confers an evaporative advantage can, for the most part, be traced to a single sentence: Mount (390.8,42) seems only to be expressing an opinion in saying that "In a bare-skinned animal, like pig or man, the evaporation of water from the body surface takes up most of the heat required for the process from the body itself, and so constitutes an efficient cooling system." Nevertheless, many later authors cite this statement in substantiation of the claim that bare skin enhances sweat evaporation. I have not been able to locate any actual data (in the works of Mount or any other author) demonstrating this assertion.

As the amount of sweat on the skin

increases, the individual drops do merge to

form a continuous sheet of water. But when

a large amount of sweat is present on naked

skin, another type of inefficiency sets in —

runoff. More sweat runs off hairless skin

without evaporating. The coat of a hairy

animal acts as a sponge, retaining sweat in

position until it can evaporate. Perspiration

dripping off the body has no cooling effect,

because no heat is absorbed by runoff. In

contrast, evaporating sweat absorbs a large

amount of heat.1a But Adolph's research

indicates that about a quarter of human

sweat can be lost to runoff, even under near

optimal evaporative conditions.1b A reflective

hair coat, then, has three advantages: (1)

lower solar heat loads; (2) increased rate of

evaporation; (3) less sweat wasted on runoff.

It is therefore difficult to understand how

naked skin can be interpreted as an

"adaptation" beneficial to a savannah

hunter.

Of course, the "savannah hunter" hypothesis

is just one of many theories. Hair loss in

Homo has been the object of much

speculation (for a survey of such theories,

see 165.1). Besides those who say we lost

our hair on the savannah170and/or because

we were hunters,171there are others who

suggest we may have lost it in the forest,172

or even in the sea.173 Some authors suggest

that nakedness made us sexually

enticing174or that hairlessness became

thermally advantageous when we started

wearing clothes.175

Even if we wished to assume that humans

did at one time have a hair coat (there is

absolutely no evidence that such was the

case), these theories would not explain the advantage of a sparse coat of hair. The

hunting hypothesis is untenable because nonhuman terrestrial predators all have

thick hair coats. A similar objection can be raised to the sexual enticement scenario.

Why haven't all mammals lost their hair if nakedness is enticing? The aquatic

At 40E C (the approximate temperature of the body surface under hyperthermic conditions) the latent heat of vaporization of water is 2406 J g-1 = 575 cal g-1. The evaporation of just a half-cup of sweat is sufficient to reduce the temperature of a 150 pounds of water by an entire centigrade degree. Evaporation is essential to heat absorption. Runoff merely removes fluid from the body without cooling it (When you pour out a cup from an urn of hot coffee, the temperature of the remaining coffee stays the same.).

This rate (25% of sweat lost to run-off) is for men engaged in intense physical exercise at high temperatures (running without a shirt in the desert) (15.4). Runoff loss can thus be significant even in the desert, let alone on the more humid savannah. Adolph (15.4,93-94), for example, studied sweating in a man exercising strenuously in the desert (relative humidity: 32 percent; estimated wind speed, 10 m.p.h.; the man wore no shirt) and found that "his rate of evaporative loss was 1,300 grams per hour. His measured rate of weight loss, however, was 1690 grams per hour, exclusive of water which accumulated in his trousers." These figures indicate that 23 percent of the sweat went to runoff — even if we ignore the fact some of the water absorbed by the trousers would have run off of a naked human being. On the African savannah, the humidity and solar heat loads would be even higher because the savannah lies closer to the equator than the southwestern American desert where Adolph performed his experiments. On the savannah, then, a larger percentage of sweat would go to runoff (due to lower evaporative rates at the higher humidity) and, at the same time, a larger amount of sweat evaporation would be required to counteract the higher savannah heat loads. This waste of body fluids seems peculiar in a creature that is supposed to be the product of adaptation to a life of strenuous diurnal hunting on the open savannah.

proposal is also dubious, most small (human-sized or smaller) aquatic or semi-

aquatic mammals do have hair coats.176

The results of my evaporation experiment make it difficult for me to accept Mount's

opinion that naked skin evaporates sweat faster than hairy skin.177 For the same

reason, I doubt Wheeler's suggestion that the acquisition of erect posture by

hominids "was probably the essential pre-adaptation which made it possible for

them to shed body hair and develop extensive evaporative surfaces."178 Also

dubious is Kushlan's "vestiary hypothesis," because it proposes that the invention of

clothing left Homo free to lose his body hair and thus obtain "the most efficient

cooling system of any mammal."179 As we have seen, naked skin provides no

particular evaporative advantage.

Because nakedness is a handicap on the savannah, Newman concludes, it is

unlikely that human ancestors lost their hair after leaving the forest: "If one had to

select times when progressive denudation was not a distinct environmental

disadvantage, the choices would be between

a very early period when our ancestors were primarily forest dwellers or a very recent period when primitive clothing could provide the same protection against either solar heat or cold. The primary difficulty in arguing for the recent loss of body hair is that there seems to be no single and powerful environmental driving force other than recurrent cold that is obvious after the Pliocene epoch. Furthermore the developing complexity and efficiency of even primitive man's technology would have decreased the probability of a straightforward biological adaption … The obvious time and place where progressive denudation would have been least disadvantageous is the ancient forest habitat. Radiant energy does penetrate the forest canopy in limited amounts, [but] that portion of the spectrum which is primarily transmitted through the vegetation, the near infrared wavelengths of 0.75 to 0.93 microns, is exactly the energy best reflected by human skin (Gates, 1968180).181

Note, however, that Newman does not

explain why our ancestors lost their hair in

the same environment (forest) where apes

did not. If humans came into being via

hybridization between pigs and

chimpanzees, their genesis would almost

surely have occurred in the forest. Chimpanzees live in forests. On the basis of its

high rate of water consumption, Yang concluded the pig, too, is functionally a forest

animal.182 Human beings need more water than almost any other animal.183

Indeed, it seems incredible that a hominid would spend any more time than

necessary away from the forest. Although the savannahs of Africa were teeming

with game, they were also swarming with ferocious predators. When a human being

is chased by a lion, the first impulse is to find a tree. Consider the picture painted by

current evolutionary theory: the noble savannah hunter, naked to the brazen sun,

boldly erect on an arid and treeless plain, in indefatigable pursuit of a wary and

In desert environments human beings can lose as much as 12 liters in sweat per day (390.3,162). Since the African savannahs lie closer to the equator than do most deserts, sweat rates there should be at least as high — if not higher.

dangerous prey, indifferent to the attack of rapacious carnivores. Certainly this

description has dramatic appeal. It's like a Tarzan story. But is it plausible?

Plato's minimal definition of a human being as a "featherless biped" exploits the fact

that it is unusual for a mammal to use only two feet in the course of normal

locomotion. Since we're mammals, it's easy enough to understand the lack of

feathers. Why, though, do we go about on two feet? Human bipedality has long

been a subject of controversy. How long have human beings stood erect? How long

did the transition take from quadrupedal locomotion to bipedality? What factors

caused the change? Why have other primates not done the same?

Following in Darwin’s footsteps, a wide variety of authors have asserted that human

beings gradually developed the ability to walk on two feet in response to selective

pressures demanding that two hands be free to manipulate tools. In his book, The

Ascent of Man, Darwin stated this view succinctly: "If it be an advantage to man to

have his hands and arms free and to stand firmly on his feet, of which there can be

little doubt from his pre-eminent success in

the battle for life, then I can see no reason why it should not have been more advantageous to the progenitors of man to have become more and more erect or bipedal. The hands and arms could hardly have become perfect enough to have manufactured weapons, or to have hurled stones and spears with true aim, as long as they were habitually used for supporting the whole weight of the body … or so long as they were especially fitted for climbing trees.1

This explanation is not without its flaws. For one thing, should we conclude on the

basis of our supposedly “pre-eminent success in the battle for life” that every

human trait is superior? Isn’t this line of reasoning a bit vague and self-indulgent?

Are our hands really in any way perfect—or do we just see ourselves that way? Isn’t

it possible to “manufacture weapons” while sitting down?

And then, there is the presumption that we became “more and more erect or

bipedal.” Fossil evidence does not confirm this gradual transition. Apparently, even

very early hominids were fully bipedal. Thus, Lovejoy observes, that "for a number

of years and throughout much of the literature there has been an a priori

assumption that australopithecine locomotion and postcranial morphology were

'intermediate' between quadrupedalism and the bipedalism of modern man. There

is no basis

for this assumption...in terms of the lower limb skeleton of Australopithecus. It is often claimed, principally on the basis of this a priori assumption, that morphological features shared by both modern man and Australopithecus do not necessarily indicate similar gait patterns. Although this might be true in terms of a single feature, it is demonstrably not true when the whole mechanical pattern is considered...the only significant difference between the total biomechanical patterns of Australopithecus and H. sapiens is one that indicates that Australopithecus was at a slight advantage compared with modern man (femoral head pressure [i.e., pressure exerted by the weight of the body on the hip joint]).²

Fossil footprints preserved in volcanic ash at Laetoli, Tanzania, indicate that

hominids were fully bipedal at a very early

date (3.7 million years ago).3 Similarly,

Straus and Cave concluded that the posture

of Neanderthals was not significantly

different from that of modern humans.4 Homo erectus was also fully upright and

bipedal.5 This lack of confirmation from the fossil record leaves gradualistic

explanations of bipedalism standing on shaky ground.

Even on a hypothetical level, the idea that early humans "gradually" attained erect

posture is implausible. One must either go on all fours or stand erect. No feasible

intermediate posture exists. Hollywood portrays cave men as slumped over, arms

hanging down. Maintaining such a position

for any length of time would put an extreme

strain on the muscles of the lower back.

Millions of years of slouching, then, would

surely have produced more than a few

backaches. In fact, it seems ridiculous to

suggest that hominids went about day in,

day out, partially erect. The physical strain

would be too great, even for us with our

supposedly better-balanced bodies.

Gradualistic thought forces the conclusion

that early "human beings" spent a portion of

their time in the quadrupedal position, but

spent a gradually increasing portion of time

erect as evolution progressed. Why would

there be such a trend? Why have we

developed the ability to stand all day on two

feet?

The many physical distinctions making a

bipedal form of locomotion possible (even

necessary, for efficiency) in humans would

require many genetic alterations. Anyone

who wishes to account for the spread of

these mutations in terms of gradual

evolution must show how bipedality

increased our ability to survive and

reproduce. Yet, a comparison of human and simian modes of locomotion, suggests

bipedality does not appear to be any great boon. Supposedly, "the freeing of the

hands" made tool manipulation possible. The need for such manipulation, in turn, is

said to have necessitated enlargement of the brain.

But why must a tool maker or a tool user stand erect for long periods of time? The

hand, not the spine, seems to be the essential element in most manipulative

Pig tracks were also preserved at Laetoli (357.3,262a).

These "free" hands seem not to have been taken advantage of for more than a million years: The earliest known stone tools date from 2.6 million years ago (556.6,236), whereas indisputable evidence (Laetoli footprints) indicate that hominids were fully bipedal 3.7 million years ago (104.5; 293.8).

This notion that free hands and intelligence are connected did not originate with Darwin, although he did espouse and popularize it. Perhaps, the earliest thinker to propose it was Anaxagorus who claimed that humans became intelligent by using the hands for manipulation rather than movement. Aristotle thought the opposite (i.e., that humans used their hands because they had become intelligent).

Merfield (337.5,51) describes a favorite chimpanzee once on display at the zoological gardens in London. She was an inveterate smoker. "You could hand her a box of matches or a lighter, and she would not only use them properly, but could always be trusted to hand them back when she was finished with them."

processes. Few such activities would require anything more than the facultative

bipedality of an ape. A chimp's hands would serve as well as ours in fashioning a

spear, bow, or axe — they might even serve better: a chimpanzee has four hands.

Human beings commonly sit down to work on such projects, having no need to

stand. I can easily picture chimpanzees doing the same — chipping away at an

arrowhead or heating spear tips in a fire. Studies of these animals have

documented that their hands, too, are capable of performing subtle tasks such as

decanting a glass of wine6 or even threading a needle.7 Surely, their using rocks and

sticks to crack nuts8 is not so different from the way our forebears would have used

hand axes.

Kortlandt has shown that chimps are capable of using weapons when they choose

to do so.9 In his experiments, he presented various objects to wild chimpanzees and

recorded their reactions. In one test, he placed a stuffed leopard on the ground near

a troop of chimpanzees. The "leopard" clutched a facsimile baby chimp in its paws,

and a concealed tape recorder emitted baby cries. Presented with this

phenomenon, the apes attacked, using large broken branches as clubs. Kortlandt

says that the blows were of such force that, had the leopard been real, it would

surely have been killed. Apparently we are not the only ones with "free" hands.

Jane Goodall has documented "aimed rock throwing" behavior in free-living

chimpanzees.10 If they can carry clubs and throw rocks, then chimpanzees certainly

have the anatomical wherewithal to carry and throw a spear. Physically, chimps

may be better equipped for throwing than we are. Their arms are far stronger than

those of human beings (about four times as strong, according to van Lawick).11 Our

ancestors invented the spear thrower, a hooked stick that, in effect, lengthens the

arm, increasing the force of the throw. The arms of chimpanzees are already longer

and stronger than those of humans.

If they can carry clubs, apes should also be physically capable of stalking prey with

a spear. Human hunters do not stand erect when their quarry is nearby. Rather,

they crouch, or even crawl, and approach their prey from downwind, taking

advantage of available cover. Only at the last moment when the prey is in range do

they spring up and throw the spear. Chimpanzees are quite capable of leaping and

throwing an object simultaneously.12

For all of these reasons, then, it is at least questionable whether bipedality has

enhanced our ability to survive and reproduce. A gradualist would object that, even

if we do not understand the selective pressures involved, such pressures must,

nevertheless, have existed, and that humans otherwise would never have made the

transition to erect posture. But slow selection of minute mutations is not the sole

conceivable mechanism that can account for human bipedality.

An Analysis of Human Bipedality

If we listed all the features contributing to our upright mode of locomotion, we

would find some of those features in the chimpanzee. Nevertheless, even though

chimpanzees do walk on two feet from time to time, such is not their normal mode

of progression. They lack certain characteristics that make moving around on the

hind limbs not only convenient for human beings, but really, under most

circumstances, the only practical way of getting around. But what if pigs possessed

all of those features relevant to bipedality that apes lack. Wouldn't it then be easy

to understand why a pig-ape hybrid might walk on two feet?

All the human distinctions listed in the remainder of this section were first identified

by other writers; I've merely gathered them together. If a scholar somewhere has

claimed that a certain characteristic distinguishes human beings from chimpanzees

and that that feature contributes to bipedality, then — if I have encountered the

claim — I at least mention it. I exclude only those features that relate to the skull;

cranial features are discussed in the next section. (It will also be convenient in this

section to discuss a few skeletal distinctions of human beings not directly relating to

bipedality.)

In the literature, most features said to

contribute to human bipedality are located in

the spine and lower extremities. For

example, our gluteal muscles, large in

comparison to those of other primates13,

enhance our ability to hold our torso erect.

Ardrey observes that

As the brain co-ordinates our nervous activity, so the buttocks co-ordinate our muscular activity. No ape boasts such a muscular monument to compare with ours; and it is a failure more fundamental than his lack of a large brain.14

Certainly, the gluteus maximus is a significant portion of our anatomy. But, did apes

"fail" to alter their bodies in this respect? Or did they simply lack the potential for

doing so? Perhaps no pure primate had the potential to evolve into a human being

by gradual mutation alone. We could, however, have obtained our big rump by

other means. One has only to think of a country ham to realize that pigs, too, have

powerful buttocks. Perhaps the very first hominid had a large rump as well as many

other distinctively human features.

The Spinal Column

Centralization of the spine, another factor facilitating our erect carriage, is not seen

in other primates to the extent that it is in humans.15 With the spine shifted toward

the center of the body, a larger proportion of the trunk lies to its rear. As a result,

the anterior portion is better counterbalanced by the posterior and less effort is

required to keep the body erect. In pigs, the spine is more centralized even than our

own,16 just as ours is more centralized than an ape's.

Sonntag notes the small size of the chimpanzee gluteal muscles in comparison with those of humans (533.6,356) and that they are small, also, in the gibbons and Old World monkeys (533.8,55,65). Duckworth (158.3,179) observes that the musculature of the upper limb is almost exactly as heavy as that of the lower limb in apes but that in humans the leg muscles are three times as heavy as those of the arms. Although I have not been able to obtain exact data on swine relating to this proportion, a cursory examination of any pig will reveal that the hind legs are far more heavily muscled than the forelegs.

Centralization of the vertebral column by itself, however, does not account for the

ease with which the human body is held

erect. Many other modifications of the spine

facilitate our bipedality. At the base of the

human spine, where the lumbar vertebrae

meet the sacrum, is a sharp backward bend

known as the lumbo-sacral promontory (see

illustration below). The angle formed by this promontory is more acute on the front

side of the spine because of subsequent tapering of the sacrum. This configuration

causes the sacrum to form the roof of the pelvic cavity in human beings (instead of

the rear wall as it does in other primates).17

The human sacrum is concave on its anterior face while an ape's is rather flat. The anterior face of a pig's sacrum is markedly concave (405.5,I,35,Fig. 50).

More significantly, it brings the base of the flexible portion of the spinal column into

a position directly above the hip joints (when viewed from the side). The force

applied to the pelvis by the weight of the upper body is directed straight downward

through the hip joints and does not tend to rotate the pelvis around those joints.

When an ape is fully erect, a vertical line passing through the base of the spine falls

behind the hip joints so that a rearward twisting torque is applied to the pelvis. This

torque must be countered by constant muscular exertion.

The dorsal, backward-projecting spine of the uppermost vertebra on an ape sacrum

is too long to permit backward flexure of the lowermost lumbar. In human and

pig,the spines on the dorsal (back) face of

the sacrum are quite short and do not

interfere with bending at this point (see

illustrations above). But, do pigs have a

lumbo-sacral promontory? In anatomical

depictions of pig skeletons arranged in the

typical quadrupedal pose, no promontory is

visible. But if a human being gets down on

all fours, then the lumbar region is twisted

forward relative to the sacrum, and the

promontory disappears. Perhaps an erect pig would also develop a sharp bend at

the base of the spine. Obviously, pigs do not ordinarily stand upright, and I have

never seen a drawing showing the configuration of a pig skeleton in such a position.

Nevertheless, anyone willing to examine a hanging side of pork will see that a

lumbo-sacral promontory is evident. Hanging a halved carcass by the hind leg

causes the leg to swing into a position that closely approximates erect human

posture. Here, again, porcine anatomy

accounts for a human peculiarity.

The human spine contains more lumbar

vertebrae and fewer sacral vertebrae than

does the spinal column of any great ape.18

Because sacrals are fused and lumbars are

not, the human spine is much more flexible

Barone (55.1,I,439) states that "on the dorsal face of the [pig sacrum] extreme reduction of the dorsal spines is quite characteristic." (translated by E.M. McCarthy)

Krider et al. (280.5,Fig 4-1) provide a photograph of a pig carcass in this position. A lumbo-sacral promontory is clearly visible.

Schultz (495.7,77) also points out that "the proportionate length of the lumbar region of man surpasses that of the man-like apes more than [would be] expected from the differences in the lumbar segments." In man the length of the lumbar region is 38 percent of the total length of the trunk, while in the chimpanzee this region is only 22 percent of trunk length.

than an ape's. Consequently, we are capable of bending the body backward until it

balances over the hip joints (without rotating the pelvis backward). The "small" of

the human back is the external evidence of this backward curvature of the lumbars.

Pigs have even fewer sacrals19 than do human beings, and they have more

lumbars.20 So here, again, humans are intermediate between apes and pigs.

Cervical vertebra (pig). Tracing.

Cervical vertebra (human)

Cervical vertebra (ape)

In all the great apes, the cervical (neck) vertebrae have long dorsal spines —

significantly longer than those on their thoracic (ribbed) vertebrae.21 In

consequence, ape necks are stiff in comparison with a human being's. Any nodding

motion of the head is severely limited.22 Though all cervical spines are long in apes,

the fourth and fifth are usually longer than the sixth and seventh. Humans and pigs,

on the other hand, have relatively short cervical spines except on the seventh

cervical, where the spine is long (but not so long as the thoracic spines).23As a

result, humans are better able than apes to adjust the balance of the head by tilting

it backward to the equilibrium point. Moreover, the figures above clearly show that

human cervicals are generally more similar to a pig's than to those of an ape.

Note that the great flexibility of the human neck in comparison with that of apes would make it possible to balance the head, almost regardless of the positioning of the foramen magnum. If the head's ability to swing backward and forward is not limited by long spines on the neck vertebrae, then a balance point will be attainable.

While it is commonly noted that the dorsal spines of the cervical vertebrae slant caudally in Homo, it has also been observed (540.6, 223) that "nonretroverted cervical spinous processes occur frequently in modern Europeans with perfectly normal posture." In the accompanying radiograph tracing (540.6,Fig. 5,223) spines 6 and 7 slope cranially. Pig cervical spines are so short that it is difficult to determine which way they slant except for the long one on the seventh cervical which slants slightly caudally (55.1).

The seventh human cervical vertebra differs in another respect from those of other

primates: it has transverse foramens or "foramina" (see illustration below). These

large openings on either side of the spinal canal "are very rarely missing in even the

seventh vertebra of Homo sapiens, but in the other primates it is rare to find

corresponding foramina in this segment" (Schultz24). In a work on the comparative

anatomy of humans and domestic animals, Barone discusses the seventh vertebra,

saying it "is not, in general, pierced by a transverse foramen, with the exception of

pigs and human beings. In these two cases it always is."25

Seventh cervical vertebra (human)

Pelvis and Coccyx

At the opposite end of the spine are the

coccygeal vertebrae which together form the

coccyx, or tail bone. Adolph Schultz observes

that these vertebrae are fused in

chimpanzees, a lack of flexibility he terms

"puzzling."26 Under the assumption that

humans stand on a "higher" rung of the

evolutionary ladder, chimpanzees should

have a longer and more pliable "tail" than do

humans. But, in fact, the human coccyx is

not fused, but movable — especially in

females, where it bends backward when they

are giving birth.27

Schultz (495.06,429) states that "In the macaque and gorilla, as well as in the other monkeys and apes examined for these conditions, there is no fixed, bony structure opposite the pubic bones, as exists in man in the form of the lower part of the sacrum. In the former, therefore, the sacrum interferes not nearly so much with the passage of the fetus to be born, as in the latter." The obstruction of the birth canal by the sacrum in human beings reflects the shortness of the human pelvis in comparison with the simian. This shortening can be accounted for by the fact that pigs have a very short pelvis. A small pelvic opening does not interfere with parturition in swine because their newborns are relatively small in comparison with those of primates.

The human pelvis and birth canal are smaller than those of apes.28 Moreover, the

sacrum and coccyx curve inward in humans to make a sharp-pointed obstacle that

must be negotiated by an emerging infant.29 In apes there is no curvature (see

illustration above), which leaves the birth canal unobstructed.30 With their

constricted birth canals, human females experience far more difficulty in delivery

than do their simian counterparts. "Parturition in the great apes is normally a rapid

process," according to primatologist A. F. Dixson, who further states that

Gorillas, orangutans and chimpanzees typically give birth in less than one hour and in most cases there is little sign that parturition is imminent … The rapidity with which the great apes give birth correlates with the fact that the head of the newborn is remarkably small in comparison to the female's pelvic canal. In human females, by contrast, labor may be prolonged and the baby's large head is often turned sideways to facilitate its passage through the canal.31

Turning of the head occurs in Homo sapiens

because the pelvis is so short that the birth

canal is wider than it is high (unlike other

primates).32 In humans, the height (antero-

posterior diameter) of the birth canal

depends on the length of the coccyx and,

specifically, on how closely the tip of the coccyx approaches the front wall of the

passage.

The human coccyx, then, ought to be relatively short, since the human neonate is

larger than any newborn ape. And yet, "man

is distinct among higher primates by

possessing the largest average number of

coccygeal vertebrae, i.e., by having been so

far affected least by the evolutionary trend

to reduce the tail" (Schultz33). "In the human

coccyx there may be as many as six

elements, in the anthropoids there are quite

commonly only two. The anthropoids have

gone further than man in the reduction of

the tail" (Jones34). This longer "tail" is difficult

to account for in terms of natural selection.

With respect to reproduction, it is clearly a negative factor. Nor does it have any

evident utility in other respects. Perhaps we should look elsewhere for an

explanation. The sacrum of a pig is curved on its inner side much like that of a

human being (see illustration above). Obviously, pigs have tails, albeit short ones. If

Homo is a hybrid of ape and pig, we expect the human sacrum to be curved and the

coccyx to be longer and more flexible than an ape's. The human pelvis is peculiar in

many respects. According to Adolph Schultz,

"The antero-posterior diameter extends from the tip of the coccyx to the lower part of the pubic symphysis," says Gray (220.1,267). "It varies with the length of the coccyx, and is capable of increase or diminution, on account of the mobility of that bone."

Contrary to popular belief, it is not merely the human head, but the entire body that is larger than that of any ape at birth (460.5,73,Table 3). Even the gorilla does not catch up with human babies in size until the second year (460.5,74,Fig. 10). This may be a manifestation of heterosis. In proportion to body size, the head of a new-born ape is as large as that of a human being. In both cases, the brain composes about 12 percent of body weight (188.7).

distinguishing characters of the human ilium [upper portion of pelvis] are so numerous and in most instances so very pronounced, whereas the ilia of all the anthropoid apes show so many basic similarities, that no theory which derives man from a gorilla-chimpanzee stock can readily account for these conditions.35

The most obvious difference is the shortness

of the human ilium. The pelvis of an ape is

about half again as long as a human's (as a

percentage of body length) and closely

approaches the last rib36 (in the great apes,

Schultz (495.7,76) notes that the iliac crest

approaches the last ribs "far more closely than in any other primates"). A pig has a

short pelvis and a wide gap between pelvis and rib cage, just as we do. The upper

blades of the pelvis run from side to side in apes but turn towards the front in

humans.37 They also turn forward in pigs.38

Lower Extremities

All nonhuman catarrhine primates have longer arms than legs.39 The reverse is the

case in humans. But pigs, like humans, have longer hind limbs than forelimbs.40 The

femur (thighbone) is the largest bone of the body. Paleoanthropologists distinguish

the femur of a hominid from an ape's in several ways. On the front of the lower end

of the femur in humans and apes, the patellar groove forms a track for the kneecap.

In apes, this groove is relatively shallow and its medial lip is more prominent than

the lateral.41 But in humans42 (and in pigs43) this groove is deep and the lateral lip is

the more elevated of the two.

Also, on the distal (lower) end of the femur are two condyles. In Homo, these

condyles are of approximately equal size. In pongids the medial one is markedly

larger than the lateral,44 but in pigs the

femoral condyles are almost exactly equal in

size.45 Human femoral condyles also differ in

shape from those of other primates. "In

hominids, both condyles show a distinct

elliptical shape, indicating a specialization

for maximum cartilage contact in the knee

joint only during full extension of the lower

limb. In [primate] quadrupeds, on the other hand, the condyles show no such

specialization to one position, being essentially circular in cross-sectional outline"

(Lovejoy46). Nevertheless, many non-primate quadrupeds do, in fact, have elliptical

femoral condyles. Among them are most of the domestic animals: cows, sheep,

horses, dogs — and pigs (see illustration below).47 We have no reason, then, to think that human elliptical condyles represent an adaptation aiding in bipedal locomotion.

<< A similar conclusion was reached by Straus: "The human ilium would seem most easily derived from some primitive member of a pre-anthropoid group, a form which was lacking in many of the specializations, such as reduction of the iliac tuberosity and anteacetabular spine and modification of the articular surface, exhibited by the modern great apes. I wish to emphasize here that the anthropoid-ape type of ilium is in no sense intermediate between the human and lower mammalian forms. Its peculiar specializations are quite as definite as those exhibited by man, so that it appears very unlikely that a true anthropoid-ape form of ilium could have been ancestral to the human type." Quoted in (495.06,431).

Physical anthropologists often note that the intercondylar fossa (or notch) is deeper in Homo sapiens than in pongids (325.5,308; 445.5,282; 468.2). Barone (55.1,I,693) describes the porcine intercondylar notch as "très profunde" (very deep).

Lateral views of femoral condyles in humans, non-human primates and pigs

Quadrupedal primates are bowlegged,

especially the anthropoid apes.48 Human

beings, however, are typically knock-

kneed.49 Preuschoft50 follows Kummer51in

suggesting that our knock-kneed stance is

an adaptation facilitating bipedal posture,

and bowlegs, to quadrupedal posture. But

the domestic quadrupeds (dog, horse, cow,

pig, etc.) are consistently knock-kneed.>

In pigs (and most other domestic animals), the femoral condyles rest on crescentic

menisci that are connected to the tibia (shinbone) in the same way as in humans.52

This configuration is significant because, as Tardieu53points out, Homo sapiens is

the only primate having a "crescent-shaped [lateral] meniscus with two tibial

insertions." In fact, in the vast majority of catarrhine primates (including the

chimpanzee and gorilla) the lateral meniscus is ring-shaped. In the tibia itself the

most prominent difference is the presence of

a long malleolus medialis in nonhuman

primates.54 In Homo this downwardly

directed, spike-like process is reduced to

little more than a nub. In pigs it is so short as

to be nearly nonexistent.55

We find another human distinction in the

foot, in the joint between the heel bone

Lovejoy (325.5,310) suggests that a prominent lateral lip is an adaptation "directly related to a valgus knee position produced by a high bicondylar angle." The horse, however, has a very high bicondylar angle (that is, it is quite knock-kneed) and yet the medial lip is much more prominent than the lateral. Knock-knees, then, do not always result in a prominent lateral lip.

Approximate measurements I have taken from anatomical drawings (405.5,I,89) give a bicondylar angle of about 15 degrees for the pig femur, which suggests that pigs are more knock-kneed than most human beings.

Romer (470.4,273) remarks that, in artiodactyls, "the astragalus is the most characteristic bone in the skeleton, for it has not only a rolling pulley above, but an equally developed lower pulley surface [articulating with the calcaneus]. This type of articulation gives very great freedom of motion to the ankle for flexion and extension of the limb and a potential springing motion, but limits the movement to a straight fore-and-aft drive even more strictly than is the case in perissodactyls [odd-toed ungulates]."

(calcaneus) and the anklebone (astragalus). Szalay and Delson note that one

feature distinguishing hominids from apes is the "loss of [the] ancestral helical

astragalo-calcaneal articulation, reducing the possible range of movements in this

joint."56 In apes the articulation is "helical" because the joint allows rotation of the

foot in a plane parallel to the ground. In Homo sapiens, this joint is more like a

hinge. It allows only flexion and extension.57 A pig, too, has a hinge-type articulation

between the calcaneus and the astragalus.

The proportions of the human foot are also

peculiar for a primate. Duckworth notes that

the human heel bone is longer than that of

apes.58 Baba found that the length of the

third metatarsal bone exceeded the length

of the calcaneus in all primates in his survey

— except in humans, in which the calcaneus

is slightly longer(the third metatarsal

connects the middle toe with the ankle and

composes most of the length of the foot

between the ankle and ball of the foot).59 Our

high ratio of calcaneus to metatarsal makes

it easier for us to bear the body's weight on

the ball of the foot (as we do each time we take a normal step), because the

forepart of the foot and the heel bone can be thought of as two ends of a lever

having the ankle as a fulcrum. As in humans, the heel bone is a bit longer than the

third metatarsal in domestic pigs.60

Our fingers and toes, are short compared to

those of apes.61 Our metacarpal bones and

phalanges are shorter than a chimpanzee's

(not

just in

relation to the overall length of the

hand, but absolutely).62 This shortening can

be explained by referring to the anatomy

of pigs: their digits are even shorter and

stubbier, than our own (which, of

course, is the case for most

quadrupeds).

Lastly, consider the ungual

tuberosities. These small, hoof-shaped

processes tip the bones (nail

phalanges) that underlie the nails of

our fingers and toes (see illustration

below). Nonhuman primates do not

have such processes. "When comparing the

The upper surface of the talus in human beings is level from side-to-side so that it is parallel to the base of the foot (542.8,52). In chimpanzees (ibid.) this surface lies at an angle so that a perpendicular to it passes through the lateral side of the sole of the foot — this angulation affects the way apes walk when upright. In taking a step, all of the pressure is placed on the outside edge of the foot. Instead of rising on its toes at the end of a step, an ape rolls the pressure point forward along the side of the foot in a rocking motion. According to Sisson (525.3,184,Fig. 197) the porcine tibiotarsal joint is level, as it is in human beings.

The fact that our toes are shorter than our fingers can be accounted for under the hybrid hypothesis by the fact that in chimpanzees the toes are markedly shorter than the fingers.

Shrewsbury and Sonek (510.6,237) feel that the difference between human nail phalanges and those of other primates is so marked that a distinction in terminology is called for, saying, "For humans we reserve the diagnostic term ungual tuft; for non-human primates the term ungual tuberosity is to be employed … [because] the roughened development of the volar aspect of a broadened ungular tuft, characteristic of humans, is not evident in the prevailingly conical ungual tuberosities of the other primates." While it does seem that a distinction in terminology is called for, it makes more sense to use a new term in connection with nonhuman primates instead of with human beings, because the term ungual tuberosity was originally used in describing humans. Moreover, no tubercle being present in these animals, the choice of the term tuberosity seems inappropriate.

nail phalanges of apes to those of man, a pronounced slenderness of the former can

be observed. If the impressive strength of pongid hands is taken into consideration,

this is surprising" (Preuschoft63). Shrewsbury and Johnson state that "the

distinguishing features of the human distal phalanx are the broad spade-like

tuberosity with proximal projecting spine and the wide diaphysis, which is concave

palmarly to create an ungual fossa. These features are not seen in primates such as

the monkey and gorilla."64 This distinction, which was also present the various

extinct hominids (395.5,539,541), has been explained as an adaptation facilitating

the manipulation of objects with the fingertips. If such is the case, why should these

processes also be found on the tips of our toes? Do these hoof-like ungual

tuberosities actually reflect a relationship between humans and ungulates like the

pig? That is, are they vestiges of ancestral hooves?

Human distal phalanx (ungual tuberosities circled in red).

Convergence or Relationship?

Our hypotheses have accounted for a number of traits in Homo. From the standard

neo-Darwinian perspective, it is hard to understand why the parallels between

human being and pig should be so

extensive. Biologists call the existence of

similar traits in animals that they consider to

be distantly related analogy. They say

analogy is found when animals live under

similar conditions or have similar habits. The same needs in each case are supposed

to cause structures of similar function to develop during the course of evolution. But

when the organisms under consideration are considered to be closely related, such

features are termed homologous. Homologous features are usually judged to be so

Elsewhere on this website, some of the problems with thinking in terms of homology and analogy are considered at length. Access this discussion >>

when the similarities are numerous and extend to detail. As Dobzhansky et al. put

it, "Examination of the structure of convergent features usually makes it possible to

detect analogy because resemblance rarely extends into the fine details of complex

traits."65

In this section we have considered one complex trait (bipedality) in a fair amount of

detail. Any attempt to account for these details in terms of natural selection seems

inadequate. It is difficult to see what “selective pressures” could have caused

human beings and pigs to “converge” in so many different respects. Under neo-

Darwinian theory, to explain most of the human features that we have just

discussed, we have to posit pressures selecting for bipedality (some human

features — long tail bone and ungual tuberosities — cannot be explained in this

way). But pigs are quadrupeds. How will we account for the fact that they, too, have

these features? Perhaps it is all just a coincidence, but after a certain point

coincidence begins to assume the color of relationship.