Primate Evolution Chapter 16

Primates (a group of mammals) majority live in trees (arboreal) include lemurs, monkeys, apes, and humans

Primate characteristics Opposable thumb Binocular vision – allows for greater depth perception Flexible joints Some with prehensile tails Large brains

Opposable thumb a thumb that can cross the palm to meet the other fingertips Adaptation: gripping object

Tarsiers and anthropoids Humans and apes are in a group called hominoids. Monkeys are divided into two groups: Old World and New World. Who are we most closely related to?

New World monkeys Habitat: rainforests of Central and South America Prehensile tail: able to grasp and hold with this fifth limb, It is associated with tree living. Squirrel monkey

Old World monkeys Larger than New World monkeys Tails that are not prehensile Appear superficially to be like hominoid apes except that apes lack tails. Habitat: diverse, including African savanna and Japanese mountains Mandril

Hominoid apes: orangutans, gibbons, chimpanzees, bonobos, and gorillas long, muscled forelimbs climbing in trees swinging from branches knuckle walking Bonobo knuckle-walking

Hominoid apes May be arboreal but mostly spends time on the ground Defined social structure and behaviors (including grooming)

Hominoid humans Even larger brain capacity than apes Upright stature Note the differences in brain capacity of the skulls: left to right, ape, chimp, human

Where did hominoids come from? Scientists believed that Old World and New World monkey shared a common anthropoid ancestor. From DNA evidence, scientists believe this to be the order of ape evolution: gibbons, orangutans, African apes, gorillas, and chimpanzees.

Comparing DNA of humans and chimps Humans and chimps share the greatest sequence of DNA nucleotides. This implies that humans and chimps are more likely to share a recent ancestor. This does not imply that humans descended from chimps.

Human evolution Fossil and DNA evidence indicates that about 5 to 8 million years ago, an ancestral hominoid diverged into two pathways: chimps and humans. Changes in food supply and climate favored those hominoids that could forage for food on land rather than in trees.

Characteristics for non-arboreal primates Bipedal: using two legs for upright walking Upright posture: facilitates primate to see farther Bipedal hominoid primates are called hominids and include humans. Bipedalism is a more adapted behavior than knuckle-walking apes.

How do scientists know that early hominids walked upright? The opening in the skull where the spinal cord attaches shows how the head and spine are positioned. Anthropologist Raymond Dart discovered an early skull that appeared ape-like but had the spinal attachment position like modern humans. Notice how the angle of the arrow changes with the human skull as compared to the ape and chimp.

Australopithecus africanus The skull that Dart discovered was named A. africanus. Estimated age: 2.5 to 2.8 MYO These primates are called australopithecines (apelike and humanlike).

1974 discovered australopithecine Lucy Australopithecus afarensis, dated about 2-3 MYO, shows pelvis structures that would indicate bipedalism. Bipedalism evolved before larger brains!

Comparing skulls and pelvic bones Chimps Early hominid Modern human Similar brain case size between these two Shorter and wider pelvic bones indicate bipedalism.

Australopithecine extinction Fossil records indicate a disappearance about 2.0-2.5 MYA. Hominids more like modern humans with larger brain cases may have evolved next. In 1964, Louis and Mary Leakey discovered skulls more like modern humans in Tanzania and named this group Homo.

Homo habilis “handy man” Ancient stone tools found near the fossils of H. habilis Estimated age: 1.5-2.5 MYO Examples of tools that H. habilis may have used

Homo erectus may have evolved from H. habilis.

H. erectus characteristics Larger brain than H. habilis More human-like face

H. erectus Stone hand axe were found near H. erectus fossils, indicating they hunted. Hearths with charred bones found in H. erectus caves indicate that they may have used fire.

H. erectus migration About 1 MYA, H. erectus migrated throughout Africa, Asia, and Europe. They became extinct between 130,000 and 300,000 years ago. This is about the time that Homo sapiens fossils appear in the fossil record (100,000-500,000 YA).

Neanderthals – Homo group 35,000-100,000 YA in Europe, Asia, and Middle East Larger brain cases than H. erectus Prominent nose Thick bones May be a sister species to modern humans (not direct ancestor) Lived about the same time as Cro-Magnon How did we know that Neanderthals were a distinct species from modern humans?

Cro-Magnon – early humans 35,000-40,000 YA Same height, skull structure, tooth structure, and brain size as modern humans Toolmakers and artists Language

Possible appearance of Cro-Magnon

Early humans crossing land bridge 12,000 years ago, evidence shows that they crossed a land bridge into North America. They built settlements and domesticated animals. Modern coastline Ancient coastline Ice sheets 21,000 yrs ago Ice sheets 12,000 yrs ago Possible migration route

Questions to think about… Is our fossil record complete? No What evidence proves that Homo erectus was more intelligent then its ancestors? Homo erectus made tools and fire What in the skull fossil record would indicate increased intelligence? Increased brain cavity size What in the skull fossil record would have the most impact on diet? Decreased teeth size

Questions to think about… What factor played a large role in human evolution? Climate changes that forced primates to look for new food sources Where do you think the Drikika Baby’s relatives spent most of its time if they are considered better climbers then modern humans? In the trees