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 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

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

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

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

Section 2: Hominid Evolution: Human Ancestors and Relatives 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 centimeters Enormously 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 upright An essential step in the evolution of our species from an apelike ancestor

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”

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

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

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 sites Must 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