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Biology
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32-3 Primates and Human Origins
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32-3 Primates and Human Origins
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What Is a Primate?
What characteristics do all primates share?
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What Is a Primate?
What Is a Primate?
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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What Is a Primate?
Fingers, Toes, and Shoulders
Flexible digits enable primates to run along tree limbs and swing from branch to branch with ease.
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What Is a Primate?
Primates’ arms are well adapted to climbing because they can rotate in broad circles around a strong shoulder joint.
In most primates, the thumb and big toe can move against the other digits. 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 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
What are the major evolutionary groups of primates?
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Evolution of Primates
Evolution of Primates
The two main groups of primates are prosimians and anthropoids.
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Evolution of Primates
Tarsiers Old World monkeys
Primate ancestor
Hominoids
Lorises and bush babiesLemurs
New World
monkeys Gibbons Orangutans Gorillas Chimpanzees Humans
Anthropoids
Prosimians
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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.
Living prosimians include bush babies, lemurs, lorises, and tarsiers.
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Evolution of Primates
Lorises and bush babies Lemurs Tarsiers
Primate ancestor
Prosimians
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Evolution of Primates
Anthropoids
Humans, apes, and most monkeys belong to a group called 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
Orangutans Chimpanzees Old World monkeys
New World monkeys Gibbons Gorillas Humans
Anthropoids
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Evolution of Primates
One branch of anthropoids is the New World monkeys. New World 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.
• Old World monkeys live in trees but lack prehensile tails.
• Great apes, also called hominoids, include gibbons, orangutans, gorillas, chimpanzees, and humans.
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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.
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Hominid Evolution
Modern human
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Hominid Evolution
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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
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
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.
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.
The structure of Australopithecus teeth suggests a diet rich in fruit.
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Hominid Evolution
The best known species is Australopithecus afarensis—based on a female skeleton named Lucy, who was 1 meter tall.
Members of the Australopithecus species were bipedal and spent some time in trees.
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Hominid Evolution
Paranthropus
The Paranthropus species had huge, grinding back teeth.
Their diets probably included coarse and fibrous plant foods.
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Hominid Evolution
Recent Hominid Discoveries
In 2001, a team had 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
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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Hominid Evolution
Sahelanthropus tchadensis
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Hominid Evolution
What is the current scientific thinking about hominid evolution?
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Hominid Evolution
Rethinking Early Hominid Evolution
Researchers once thought that human evolution took place in steps, in which hominid species became gradually more humanlike.
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Hominid Evolution
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
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.
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The Road to Modern Humans
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.
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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, so researchers called the species Homo habilis, which means “handy man.”
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The Road to Modern Humans
2 million years ago, a 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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The Road to Modern Humans
Out of Africa—But Who and When?
Evidence suggests that hominids left Africa in several waves, as shown in the following diagram.
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The Road to Modern Humans
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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.
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The Road to Modern Humans
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.
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Modern Homo sapiens
The earliest of these species is called Homo neanderthalensis.
Neanderthals lived in Europe and Asia 200,000–30,000 years ago.
They made stone tools and lived in organized social groups.
The other group is Homo sapiens—people whose skeletons look like those of modern humans.
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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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The Road to Modern Humans
About 40,000 years ago, a group known as Cro-Magnons appeared in Europe.
By 30,000 years ago, Neanderthals had disappeared from Europe and the Middle East.
Since that time, our species has been Earth’s only hominid.
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32-3
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32-3
The ability to merge visual images from both eyes is called
a. monocular vision.
b. binocular vision.
c. overlapping vision.
d. color vision.
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Which of the following is true about hominid evolution?
a. The development of a large brain happened before bipedal locomotion.
b. There is a straight line of descent from the earliest hominid species to Homo sapiens.
c. The genus Homo appeared before the genus Australopithecus.
d. 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
a. increased brain size.
b. made it easier to see.
c. freed both hands to use tools.
d. allowed easier escape from predators.
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The multi-regional model hypothesizes that
a. Homo sapiens evolved independently in several parts of the world.
b. Modern humans evolved in Africa, then migrated to various parts of the world.
c. Neanderthals produced cave drawings.
d. Homo habilis descended from Homo erectus.
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32-3
The oldest known Homo sapiens skeletons are about
a. 6,000 years old.
b. 100,000 years old.
c. 3 million years old.
d. 30 million years old.
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