Primates and Human Origins

1. 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. 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