1. 32-3 Primates and Human Origins
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What Is a Primate?
What Is a Primate?
Primates means “first” in Latin.
Primates share several important adaptations, many of which are extremely useful for a life spent mainly in trees.
In general, primates have binocular vision, a well- developed cerebrum, relatively long fingers and toes, and arms that can rotate around their shoulder joints.
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3. Fingers, Toes, and Shoulders
What Is a Primate?
Fingers, Toes, and Shoulders
Primates normally have five flexible fingers that can curl around objects and flexible toes.
Flexible digits enable primates to run along tree limbs and swing from branch to branch with ease.
Primates’ arms are well adapted to climbing as they rotate in broad circles around a strong shoulder joint.
In most primates, the thumb and big toe can move against the other digits, also called an opposable thumb.
This characteristic allows primates to hold objects in their hands or feet.
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What Is a Primate?
Well-Developed Cerebrum
The large cerebrum, including a well-developed cerebral cortex, of primates enables them to display more complex behaviors than many other mammals.
Many species have social behaviors that include adoption of orphans and even warfare between rival primate troops.
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What Is a Primate?
Binocular Vision 
Many primates have a flat face, so both eyes face forward with overlapping fields of view. This facial structure allows for binocular vision.
Binocular vision is the ability to merge visual images from both eyes, providing depth perception and a three-dimensional view of the world.
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Evolution of Primates
Evolution of Primates
Humans and other primates evolved from a common ancestor that lived more than 65 million years ago.
The two main groups of primates are prosimians and anthropoids.
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Evolution of Primates
Prosimians 
Most prosimians alive today are small, nocturnal primates with large eyes that are adapted to seeing in the dark. Many have dog-like snouts.
Living prosimians include bush babies, lemurs, lorises, and tarsiers.
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Evolution of Primates
Anthropoids  
Humans, apes, and most monkeys belong to the anthropoids, which means humanlike primates.
This group split early in its evolutionary history into two major branches.
These branches separated as drifting continents moved apart.
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Evolution of Primates
One branch of anthropoids is the New World monkeys. New World monkeys:
are found today in Central and South America.
include squirrel monkeys and spider monkeys.
live almost entirely in trees.
have long, flexible arms to swing from branches.
have a prehensile tail, which is a tail that can coil around a branch to serve as a “fifth hand.”
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Evolution of Primates
The other group of anthropoids includes Old World monkeys and great apes.
Evolved in Africa and Asia.
Old World monkeys live in trees but lack prehensile tails (langurs and macaques).
Great apes, also called hominoids, include gibbons, orangutans, gorillas, chimpanzees, and humans.
Chimpanzees are humans’ closest relatives among the great apes, sharing 98% of their DNA.
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Evolution of Primates
New World monkeys
Old World monkeys
Gibbons
Orangutans
Gorillas
Chimpanzees
Humans
Anthropoids
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Hominid Evolution
Hominid Evolution
Between 6 and 7 million years ago, the hominoid line gave rise to hominids.
The hominid family includes modern humans.
As hominids evolved, they began to walk upright and developed thumbs adapted for grasping.
They also developed large brains.
Hominids displayed a remarkable increase in brain size, especially in an expanded cerebrum—the “thinking” area of the brain.
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Hominid Evolution
The skull, neck, spinal column, hipbones, and leg bones of early hominid species changed shape in ways that enabled later hominid species to walk upright.
Evolution of this bipedal, or two-foot, locomotion freed both hands to use tools.
Hominids evolved an opposable thumb that enabled grasping objects and using tools.
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Hominid Evolution
Modern human
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Hominid Evolution
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Hominid Evolution
Early Hominids 
At present, the hominid fossil record includes these genera:
Ardipithecus
Australopithecus
Paranthropus
Kenyanthropus
Homo
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Hominid Evolution
There are as many as 20 separate hominid species.
This diverse group of hominid fossils covers roughly 6 million years.
All are relatives of modern humans, but not all are human ancestors.
Almost a third of all known hominid species have been discovered in the last years.
Questions remain about how fossil hominids are related to one another and to humans.
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Hominid Evolution
Australopithecus 
An early hominid species, Australopithecus, lived from about 4 million to 1 million years ago.
Bipedal apes that spent at least some time in trees
The structure of their teeth suggests a diet rich in fruit.
Some species may have been human ancestors, while others formed separate branches.
The best known species is Australopithecus afarensis—based on a female skeleton named Lucy, who was 1 meter tall.
Members of the Australopithecus species had small brains, were bipedal, and spent some time in trees.
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Hominid Evolution
Paranthropus 
The Paranthropus species had huge, grinding back teeth and grew to the size of well-fed football linebackers.
Their diets probably included coarse and fibrous plant foods like those eaten by modern gorillas.
Most paleontologists place Paranthropus on a separate, dead-end branch of our family tree.
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20. Recent Hominid Discoveries
Hominid Evolution
Recent Hominid Discoveries 
In 2001, a team lead by Meave Leakey discovered a skull in Kenya.
Its ear resembled a chimpanzee’s.
Its brain was small.
Its facial features resembled those of Homo fossils.
It was put in a new genus, Kenyanthropus, which lived at the same time as A. afarensis.
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Hominid Evolution
Photo Credit: left: Fred Spoor, copyright National Museum of Kenya; right: Animals Animals/©E.R. Degginger
Kenyanthropus platyops
Homo erectus
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Hominid Evolution
In 2002, paleontologists working in the desert in north-central Africa discovered another skull.
Called Sahelanthropus, it is nearly 7 million years old.
If it is a hominid, it would be a million years older than any hominid previously known.
It had a brain like a modern chimp and a flat face like a human.
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23. Sahelanthropus tchadensis
Hominid Evolution
Photo Credit: copyright M.P.F.T.
Sahelanthropus tchadensis
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24. Rethinking Early Hominid Evolution
Researchers once thought that human evolution took place in steps, in which hominid species became gradually more humanlike.
Hominid evolution did not proceed by the simple, straight-line transformation of one species into another.
Rather, a series of complex adaptive radiations produced a large number of species whose relationships are difficult to determine.
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Hominid Evolution
The diagram shows fossil hominids and the time ranges during which they may have existed. The time ranges are likely to change as paleontologists gather new data. The question mark after Sahelanthropus tchadensis indicates that scientists are not yet certain that this species is a hominid. Paleontologists do not yet have enough information to know how hominid species are related. It is now clear that hominid evolution did not proceed by the simple, straight-line transformation of one species into another. Current hypotheses about early stages of human evolution recognize the incompleteness of the data.
Millions of years ago
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Hominid Evolution
The hominid fossil record dates back 7 million years, close to the time that DNA studies suggest for the split between hominids and the ancestors of modern chimpanzees.
There are many known fossil hominid species, several of which display a confusing mix of primative and modern traits.
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27. The Road to Modern Humans
Paleontologists still do not completely understand the history and relationships of species within our own genus.
Other species in the genus Homo existed before Homo sapiens and at least two other species in the genus Homo existed at the same time as early humans.
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28. The Road to Modern Humans
The Genus Homo
The first fossils in the genus Homo are about 2.5 million years old.
These fossils were found with tools made of stone and bone, so researchers called the species Homo habilis, which means “handy man.”
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29. The Road to Modern Humans
2 million years ago, a larger species called Homo ergaster appeared.
It had a bigger brain and downward-facing nostrils that resembled those of modern humans.
At some point, either H. ergaster or a related species named Homo erectus began migrating out of Africa through the Middle East.
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30. The Road to Modern Humans
Out of Africa—But Who and When?
Researchers agree that our genus originated in Africa.
Evidence suggests that hominids left Africa in several waves, as shown in the following diagram.
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31. The Road to Modern Humans
It is not certain where and when Homo sapiens arose.
One hypothesis, the multi-regional model, suggests that modern humans evolved independently in several parts of the world from widely separated populations of H. erectus.
Another hypothesis, the out-of-Africa model, proposes that modern humans evolved in Africa between 200,000–150,000 years ago, migrated out to colonize the world, and replaced the descendants of earlier hominid species.
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Modern Homo sapiens
Modern Homo sapiens
The story of modern humans over the past 500,000 years involves two main groups.
The earliest of these species is called Homo neanderthalensis, named after the Neander Valley in Germany where their remains were first found.
Neanderthals lived in Europe and western Asia 200,000–30,000 years ago.
They made stone tools and lived in organized social groups.
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Modern Homo sapiens
The other group is Homo sapiens—people whose skeletons look like those of modern humans.
Probably arose in Africa and appeared in the Middle East around 100,000 years ago.
Neanderthals and Homo sapiens lived side by side in what is now Israel, Lebanon, Syria, and Turkey for around 50,000 years, using similar tools and living in remarkably similar ways.
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34. The Road to Modern Humans
50,000–40,000 years ago some populations of H. sapiens seem to have changed their way of life:
They made more sophisticated stone blades and elaborately worked tools from bones and antlers.
They produced cave paintings.
They buried their dead with elaborate rituals.
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35. The Road to Modern Humans
About 40,000 years ago, one such group known as Cro-Magnons appeared in Europe.
By 30,000 years ago, Neanderthals had disappeared from Europe and the Middle East. How and why is still not known.
Since that time, our species has been Earth’s only hominid.
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32-3
The ability to merge visual images from both eyes is called
monocular vision.
binocular vision.
overlapping vision.
color vision.
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32-3
Which of the following is true about hominid evolution?
The development of a large brain happened before bipedal locomotion.
There is a straight line of descent from the earliest hominid species to Homo sapiens.
The genus Homo appeared before the genus Australopithecus.
Hominid evolution took place as a series of adaptive radiations that produced a large number of species.
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32-3
The evolution of bipedal locomotion was important because it
increased brain size.
made it easier to see.
freed both hands to use tools.
allowed easier escape from predators.
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32-3
The multi-regional model hypothesizes that
Homo sapiens evolved independently in several parts of the world.
Modern humans evolved in Africa, then migrated to various parts of the world.
Neanderthals produced cave drawings.
Homo habilis descended from Homo erectus.
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32-3
The oldest known Homo sapiens skeletons are about
6,000 years old.
100,000 years old.
3 million years old.
30 million years old.
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