origins of humanity

Origins of Humanity

Earliest Beginning

Characteristics of Ancestors

Early Behavior

Earliest Beginnings

Ca. 25-5 million years ago (mya) Miocene primates

Ca. 6-2 mya Hominids, early culture

Miocene Primate Evolution The Miocene epoch (25-5 mya) -

"The Golden Age of Apes" Two major hominoid radiations

The dryopiths - Early to Middle Miocene (25-15 mya)

The ramapiths - Middle to Late Miocene (15-5 mya)

Dryopithecus

Ramapiths (Sivapithecus)

Gigantopithecus

Gigantopithecus is known to have lived in what is now China and Southeast Asia.

Gigantopithecus was the largest primate that ever walked the Earth. He would have risen 9 to 10 feet high if he choose to stand up on only his hind legs, and probably weighed about 600 lbs (a mountain gorilla male weigh about 400 lbs).

Some suggest that Gigantopithecus is not extinct, but is hiding in remote areas of the Himalaya Mountains or the forests of North-West America. Could a Gigantopithecus, or his descendants, be the source of the Yeti or Bigfoot tales?

http://www.unmuseum.org/bigape.htm

Size Differences

http://www.unmuseum.org/bigape.htm

Our Last Common Ancestor?

Unable to determine exact specimen as yet (Dryopith or Ramapith)

Molecular data suggests split occurred between 6 and 5 million years ago.

Extensive genetic diversity in hominoids during the Miocene makes things complicated.

Scientific Evidence

Earliest humans (hominids) Evolved 5-6 million years ago in Africa Very similar to apes, but:

Characteristics Bipedal Small brain size Relatively small body size

Between 3 and 4 feet 60-100 pounds

Bipedality EvidenceAnatomy of Bipedalism

Early hominid pelvis on left, modern human on right.

Comparisons

Basal Hominids (6-4 mya)

Sahelanthropus tchadensis Ardipithecus ramidus Australopithecus anamensis Orrorin tugenensis Recent specimens that date to this time

period may represent the earliest on the human line, but not a lot of data yet. Most have small brains and were probably bipedal.

What did they look like?

tchadensis

tugenensis

anamensis

Australopithecines

Australopithecus afarensis Australopithecus africanus Australopithecus garhi

Australopithecus afarensis (ca. 3.5mya)

Australopithecus afarensis“Lucy”

Discovered by Donald Johanson and Tom Gray in 1974 at Hadar in Ethiopia (Johanson and Edey 1981; Johanson and Taieb 1976). Its age is about 3.2 million years. Lucy was an adult female of about 25 years. About 40% of her skeleton was found, and her pelvis, femur (the upper leg bone) and tibia show her to have been bipedal. She was about 107 cm (3'6") tall (small for her species) and about 28 kg (62 lbs) in weight.

Other Evidence: Laetoli footprints

• In 1976, members of a team led by Mary Leakey discovered the fossilized footprints of human ancestors in Laetoli, Africa.

• The footprints were formed 3.5 million years ago when at least two individuals walked over wet volcanic ash. The wet ash hardened like cement and was then covered by more ash.

Laeotoli

Some analysts have noted that the smaller of the two clearest trails bears telltale signs that suggest whoever left the prints was burdened on one side -- perhaps a female carrying an infant on her hip.

The detailed interpretation of the prints remains a matter of debate, they remain an extraordinary and fascinating fossil find, preserving a moment in prehistoric time.

Laetoli

Paleoecological reconstructions for that time include bushland and aquatic fauna at Laetoli and closed woodland at Hadar. Direct evidence of bipedality in Australopithecus anamensis dates from between about 3.9 and 4.2 mya (Leakey, et. al. 1995).

http://www.pbs.org/wgbh/evolution/library/07/1/l_071_03.html

http://www.jqjacobs.net/anthro/paleo/bipedalism.html

Why Bipedal?

Three key features differentiate human and chimpanzee bipedalism: Chimpanzees are unable to extend their knee-

joints to produce a straight leg in the stance phase.

Muscular power has to be exerted to support the body.

The constantly flexed position of the chimpanzee leg also mean there is no toe off and heel strike in the swing phase.

http://www.stanford.edu/~harryg/protected/chp15.htm

Advantages of Bipedalism?

With its radically different anatomy, bipedalism clearly was an adaptation to terrestrial living, but was it an advantage over quadrapedalism?

Not necessarily faster, but likely sustainable over long distances

Protection from predators? Latest evidence for earliest hominids puts them in

forested environment, not open habitat Did free hands for tool-using, but what tools; or

possibly food transport?

Theories

The postural feeding hypothesis (Hunt 1996) is an ecological model.

The behavioral model (Lovejoy 1981) attributes bipedality to the social, sexual and reproductive conduct of early hominids.

The thermoregulatory model (Wheeler 1991) views the increased heat loss, increased cooling, reduced heat gain and reduced water requirements conferred by a bipedal stance in a hot, tropical climate as the selective pressure leading to bipedalism.


Hunt's postural feeding hypothesis

Hunt's postural feeding hypothesis asserts that the arboreal food gathering postures of arm-hanging and vertical climbing, a shared adaptation and postural specialization of apes, are sufficiently common to influence anatomy. Both chimpanzee behavior and australopithecine anatomy inform

the model. Eighty percent of chimpanzee bipedalism is during feeding with

arm-hanging stabilizing the posture 93% of the time in terminal branches and 52% in the central parts of trees.

Torso form in australopithecines features adaptations to arm-hanging, inferring australopithecine adaptation to arboreal bipedal fruit gathering.

According to Hunt, this early and specialized origin of bipedalism only later evolved into habitual bipedal locomotion.


The behavioral model

The behavioral model, as presented by Lovejoy, focuses on social behavioral mechanisms that influence survivorship and birthrate. Human sexual behavior and anatomy are

hypothesized as implying a monogamous mating structure, a social form seen as prerequisite to male provisioning.

Provisioning behavior with the upper limbs used to transport food to a mate and offspring is seen as a strong selection factor for bipedality by directly improving offspring survivorship and increasing reproductive rate.


Wheeler's thermoregulatory model Wheeler's thermoregulatory model proposes, as

the selective pressure, bipedalism conferring reduction in heat gain and facilitation of heat dissipation. Bipedalism raises the mean body surface higher

above the ground, where more favorable wind speeds and temperatures prevail.

Greater wind flow translates to higher convective heat loss.

Bipedalism reduces evaporative cooling requirements and conserves body water.

Vertical orientation also minimizes direct solar exposure during the time of day when the solar radiation is most intense.


Do we really know?

Timing

The timing of the appearance of bipedalism is of critical importance in assessing these competing hypothesis.

The models all present plausible selective pressures needed for evolutionary change: food access, provisioning, survivorship assurance, increase in offspring, predator and injury avoidance and energy and water conservation.

Under different conditions the individual importance of these pressures will change. The important question is what conditions prevailed at the time that bipedalism appears in the fossil record.


Paleoenvironment

Vrba's "turn-over pulse" hypothesis supports a major climate change, with onset of drier conditions and diminution of wooded habitats, beginning in the Pliocene around 2.5 mya.

Habitat reconstruction based on faunal associations with hominid fossils demonstrate that Australopithecus species lived in wooded and well watered environments (Reed 1997).

Homo is the first hominid known to have adapted to open, savannah-like habitats, well after the evolution of bipedality.


Which is it?

Thus, from an paleoecological perspective, the thermoregulatory model does not fit the evidence.

With the behavioral model, which hypothesizes monogamous pair bonding and reduction in mate competition as changing social factors antecedent to bipedalism, one would expect an earlier reduction in canine size, in parallel with the evolution of bipedalism.

Arm-hanging anatomy persists long after the onset of bipedal characteristics, indicating occupation of wooded niches for the early bipedal hominids, so Hunt’s feeding model might be most appropriate.


Australopithecus africanus (ca. 3 mya)

South Africa was the home to the species Australopithecus africanus, which lived 3.3 to 2.5 million years ago.

This species was the first of the australopiths to be described; Raymond Dart named the genus and species in 1925 after his discovery of the famous Taung child.

Many features of the cranium of A. africanus are more evolved than that of earlier A. afarensis. These features include a more

globular cranium and slightly higher ratio of brain size to body size.

Also the teeth and face appear less primitive.

http://www.mnh.si.edu/anthro/humanorigins/ha/afri.html

A. africanus

For years researchers considered the evolution of early humans to pass from A. afarensis to A. africanus and lead to early Homo.

However, some researchers now believe that facial features link A. africanus to the "robust" early human species of southern Africa, Paranthropus robustus

http://www.mnh.si.edu/anthro/humanorigins/ha/afri.html

Australopithecus garhi

A. garhi existed 2.5 million years ago. Tim White and Berhame Asfaw found it in Bouri, East Ethiopia.

Characteristics: cranial capacity of 450ml. canines and premolars like Homo genus huge molars no diastema prognathic ape-like arms and legs

The importance of this hominid is that it was found with many tools and an array of slaughtered animals. Tool use has been the defining criteria that separated the Homo genus from the Australopithecines.

http://www.humboldt.edu/~mrc1/main.shtml

Genus Paranthropus

Robust Early Hominids (2.5-1.5 mya) Extinct branch/lineage Highly specialized features

Heavy brows Large teeth, particularly back Large muscle attachment areas

Paranthropus robustus

DNH 7, "Eurydice", Paranthropus robustus. Discovered by André Keyser in 1994 at the Drimolen cave in South Africa. Estimated age is

between 1.5 and 2.0 million years.

Paranthropus boisei

OH 5, "Zinjanthropus", "Nutcracker Man",

Paranthropus boisei

Discovered by Mary Leakey in 1959 at Olduvai Gorge in Tanzania (Leakey 1959). Estimated age is 1.8 million years.

Paranthropus aethiopicus

By 2.7 million years ago, a new lineage of early humans had evolved in East Africa: Paranthropus aethiopicus

http://www.mnh.si.edu/anthro/humanorigins/ha/a_tree.html

origins of humanity

Documents

middle miocene

late miocene

miocene epoch

wet ash

modern human

donald johanson

human line

ethiopia johanson