chapter 34: humans section 1: primates and human origins

Chapter 34: Humans

Section 1: Primates and Human Origins

Primates and Human Origins

Humans evolved from common ancestors we share with other living primates such as chimpanzees and apes

Our species most likely evolved in Africa and then spread around the world

We know that the first Homo sapiens appeared around 500,000 years ago Humans did not appear until dinosaurs had

been extinct for more than 60 million years

What are Primates?

As a group, primates share several important adaptations, many of which are extremely suitable to a life spent mainly in trees Faces are much flatter than those of other mammals Eyes point forward

Allow both eyes to inspect the same area at the same time

Information gathered by the eyes is processed by highly developed visual centers in the brain Produces binocular vision

3-D

What are Primates?

Snout is reduced in size Flexible fingers

Curl around objectsHold objects in hands or feetSwing from branch to branch with easeBall and socket joint at shoulder

Large and complicated cerebrumDisplay far more complex behaviors than other

animals

How Did Primates Evolve?

Very early in their history, primates split into several evolutionary lines Prosimians

Includes lemurs, lorises, and aye-ayesAlmost entirely nocturnalLarge eyes adapted for seeing in the dark

AnthropoidsIncludes monkeys, apes, and humansHas given rise to several major primate branches


Two anthropoid branches – the two major groups of monkeys and apes – separated around 45 million years ago when the continents on which they lived moved apart and were no longer connected by land bridges New World Monkeys

Evolved into the monkeys found today in Central and South America

Almost all tree dwellersPrehensile tails


Old World MonkeysExtend from Africa all the way across Asia

to Indonesia and JapanNo prehensile tailSpend most of their time on the groundIncludes hominoids

Gorillas, gibbons, orangutans, chimpanzees, and Homo sapiens

Chapter 34: Humans

Section 2: Hominid Evolution: Human Ancestors and Relatives

Hominid Evolution: Human Ancestors and Relatives

Between 4 and 9 million years ago, the hominoid line in Africa gave rise to a small group of species that we now recognize as our closest relatives Hominids Not yet human but showed several

evolutionary trends that distinguish them from other hominoids

What Are Hominids?

Hominids were omnivores that ate both meat and vegetable foods, as modern humans do

As time progressed, the spinal column, hip bones, and leg bones of these animals changed shape in ways that made it easier for them to walk upright on two legs Bipedal locomotion

What Are Hominids?

Because our ancestors could walk erect, their hands were free to use tools more often

At the same time, the thumb of the hominid hand became more and more independent from the other fingers

The evolution of an opposable thumb enabled ancient hominids to grasp objects and use them as tools more effectively than other primates

What Are Hominids?

Hominids also displayed a remarkable increase in brain size Chimpanzees, our closest relatives among the apes,

have a brain size of about 280 – 450 cubic centimeters

The brain of Homo sapiens, on the other hand, ranges in size from 1200 – 1600 cubic centimetersEnormously expanded human cerebrum

“thinking” area of the brain

How Did Hominids Evolve?

Much of our most recent evidence for hominid evolution comes from a small area in eastern Africa between Tanzania and Ethiopia

There, several researchers have found fossils of several species of hominids dating from about 4 million to about 1.5 million years ago

Australopithecus: The First Hominids

The first hominid fossil to be found, a nearly complete skull of a young child, was discovered in South Africa in 1924 Australopithecus

“Southern Ape” Because the skull belonged to a child, it could not be used to

determine how adults of the species looked But 12 years later, investigators in Africa found fossils of adult

australopithecines One of the fossils was part of a hip bone, indicating that

Australopithecus walked uprightAn essential step in the evolution of our species from an

apelike ancestor


Since those discoveries, researchers have found many more complete hominid fossils

In 1974, a team led by Donald Johanson and Tim White found a nearly complete Australopithecus skeleton

From the shape of the pelvic bone, it was clear that this skeleton had been that of a female “Lucy”


In 1977, anthropologist Mary Leakey made another discovery: a set of fossil hominid footprints

From the size of the prints, they were probably a parent and an offspring Clear evidence that the animals that made the footprints

walked erect on two legs, as humans do No stone tools have been found among Australopithecus

fossils, but they may have used twigs and stones as tools in a way similar to that of chimpanzees today


Most current studies suggest that there were at least four species of Australopithecus A. boisei A. robustus A. afarensis A. africanus

These species all lived between 4 and 1.5 million years ago, walked upright, and had much smaller brains than present-day humans

Homo habilis

For a while, australopithecines were the only known links in the chain of human evolution

Then anthropologist Richard Leakey found another hominid fossil with a smaller face and significantly larger brain than the australopithecines

Leakey felt this species was similar enough to humans to be placed in our own genus, Homo

Fossils of this hominid were found along with tools made of stone and bone

Homo habilis “handy-man”

Homo habilis

Near one of these fossil finds is the oldest human settlement yet discovered (Kenya)

The settlement was found at a level in the rock dated at 1.9 million years ago

The main site is a circular stone structure about 4 meters in diameter

Inside, the floor is littered with animal bones and stone tools

Homo erectus

Within a few hundred thousand years Homo habilis disappeared and was replaced by a larger brained species called Homo erectus

By 1 million years ago, this species had spread over most of the Old World, from Africa to Europe to Asia

Homo erectus was an excellent tool maker Carefully chipped and balanced hand axes have been

found with Homo erectus fossils throughout the world In caves in China that are at least half a million years old,

charred animal bones have been found around fire sitesMust have used fire for cooking

Homo sapiens

About 500,000 years ago, the first hominids assigned to our own species appeared

These hominids, often called archaic Homo sapiens, would not be easily recognizable as modern humans

Little is known about this species

Homo sapiens

Around 150,000 years ago, a new hominid walked on Earth

First discovered in the Neander valley in Germany, this species was called Neanderthal man, or Homo neanderthalensis

Now, based on more complete fossil evidence, Neanderthals have been placed in our own species and are called Homo sapiens neanderthalensis

Homo sapiens

Neanderthal man could probably walk down a busy street today and not be noticed

These early members of our species were successful for a time and became common throughout Europe and the Middle East by 70,000 years ago

Homo sapiens

The first hominids truly identical to modern humans appeared in locations scattered throughout the Old World roughly 100,000 years ago

These large-brained people, called Cro-Magnon, were more slender than the Neanderthals and had a more complex culture

They made a wide variety of stone and bone tools, including spear points, knives, chisels,and needles

Fossils of Cro-magnon are now classified as modern humans, Homo sapiens sapiens

Homo sapiens

Most paleontologists interpret the dates of Cro-Magnon fossils found throughout the world as indicating that modern humans originated in Africa and from there spread out over the rest of the world

However and wherever Cro-Magnons originated, there is ample fossil evidence that they lived side by side with Neanderthals in several locations for some time

Then, around 30,000 years ago, the Neanderthals disappeared

Homo sapiens

Some scientists believe that Cro-Magnons interbred with Neanderthals, blending their characteristics

Others believe that the more intelligent newcomers killed off their older relatives

In either case, only Homo sapiens sapiens remained to populate the rest of the world

chapter 34: humans section 1: primates and human origins

Documents