1. Section 1: Primates and Human Origins
Chapter 34: Humans
Section 1: Primates and Human Origins

2. 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

3. 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

4. What are Primates? Snout is reduced in size Flexible fingers
Curl around objects
Hold objects in hands or feet
Swing from branch to branch with ease
Ball and socket joint at shoulder
Large and complicated cerebrum
Display far more complex behaviors than other animals

5. How Did Primates Evolve?
Very early in their history, primates split into several evolutionary lines
Prosimians
Includes lemurs, lorises, and aye-ayes
Almost entirely nocturnal
Large eyes adapted for seeing in the dark
Anthropoids
Includes monkeys, apes, and humans
Has given rise to several major primate branches

7. How Did Primates Evolve?
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 dwellers
Prehensile tails

8. How Did Primates Evolve?
Old World Monkeys
Extend from Africa all the way across Asia to Indonesia and Japan
No prehensile tail
Spend most of their time on the ground
Includes hominoids
Gorillas, gibbons, orangutans, chimpanzees, and Homo sapiens

9. Section 2: Hominid Evolution: Human Ancestors and Relatives
Chapter 34: Humans
Section 2: Hominid Evolution: Human Ancestors and Relatives

10. 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

11. 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

12. 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

13. 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 centimeters
Enormously expanded human cerebrum
“thinking” area of the brain

15. 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

16. 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 upright
An essential step in the evolution of our species from an apelike ancestor

18. Australopithecus: The First Hominids
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”

20. Australopithecus: The First Hominids
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

21. Australopithecus: The First Hominids
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

22. 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”

23. 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

24. 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 sites
Must have used fire for cooking

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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