Chapter 22: The Evolution of Primates

\
\

Primate Adaptations

• Primates are placental mammals that arose from small, arboreal (tree-dwelling), shrew-like mammals.
  • Primates possess five grasping digits, including an opposable thumb or toe; long, slender limbs that move freely at the hips and shoulders; and eyes located in front of the head.

\

Primate Classification

• Primates are divided into three suborders.
  • The suborder Prosimii includes lemurs, galagos, and lorises.
  • The suborder Tarsiiformes includes tarsiers.
  • The suborder Anthropoidea includes anthropoids: monkeys, apes, and humans.
• Anthropoids include monkeys, apes, and humans.
  • Early anthropoids branched into two groups: New World monkeys \n and Old World monkeys.
• Hominoids include apes and humans.
  • Hominoids arose from the Old World monkey lineage.
  • There are four modern genera of apes: gibbons, orangutans, gorillas, and chimpanzees.
• The hominin line consists of humans and their ancestors.

\

Hominin Evolution

• Unlike ape skeletons, hominin skeletons have adaptations that reflect the ability to stand erect and walk on two feet.
  • These adaptations include a complex curvature of the spine; a shorter, broader pelvis; repositioning of the foramen magnum to the base of the skull; and a first toe that is aligned with the other toes.
• The human skull lacks a pronounced supraorbital ridge, is flatter than ape skulls in the front, and has a pronounced chin.
  • The human brain is larger than ape brains, and the jaw is structured so that the teeth are arranged in a U shape.
• Orrorin is an early hominin that arose about 6 mya.
  • Researchers studying the fossil leg bones of Orrorin think that it walked upright and was bipedal (walked on two feet).
• Ardipithecus, Australopithecus, and Paranthropus species are often referred to as australopithecines.
  • Australopithecines were bipedal, a hominin feature.
  • The first Ardipithecus species, Ar. kadabba, appeared about 5.8 mya.
  • Ardipithecus ramidus, which appeared about 4.8 mya, may have given rise to Australopithecus anamensis, which in turn probably gave rise to another primitive hominin, Australopithecus afarensis.
  • Many paleoanthropologists think that Au. afarensis gave rise to several australopithecine species, including Australopithecus africanus, Paranthropus spp., and possibly Homo habilis.
  • Australopithecus sediba may have descended from Au. africanus.
• Homo habilis was the earliest known hominin with some of the human features lacking in the australopithecines, including a slightly larger brain.
  • Homo habilis fashioned crude tools from stone.
• The best-known fossils of H. ergaster, which existed from 2.0 to 1.4 mya, come from Kenya.
  • Homo ergaster may be the direct ancestor of later humans.
• Homo erectus had a larger brain than H. habilis; made more sophisticated tools; and may have worn clothing, built fires, and lived in caves or shelters.
  • Homo erectus, which is probably a later Asian offshoot of H. ergaster, appears to be an evolutionary dead end.
• Archaic humans are regionally diverse descendants of H. ergaster that lived in Africa, Asia, and europe from about 1.2 mya to 200,000 years ago.
  • The brains of archaic humans were essentially the same size as our brains, although their skulls retained some ancestral characters, and they had rich and varied cultures.
• Some researchers classify the oldest archaic human fossils discovered in europe (in Spain) as Homo antecessor.
  • Homo antecessor existed from about 1.2 mya to 800,000 years ago.
• Homo heidelbergensis, which appeared about 600,000 years ago and existed until about 300,000 years ago, may have descended from H. antecessor.
  • This extinct hominin had a larger brain—similar in size to that of modern humans—than either H. ergaster or H. antecessor.
  • Many scientists studying H. heidelbergensis think that both Neandertals and modern humans descended from it.
• Neandertals lived from about 250,000 to 28,000 years ago.
  • Neandertals had short, sturdy builds; receding chins and foreheads; heavy supraorbital ridges and jawbones; larger front teeth; and nasal cavities with unusual triangular bony projections. \n Many scientists think that Neandertals were a separate species,Homo neanderthalensis.
• Homo sapiens, anatomically modern humans, existed in Africa about 195,000 years ago.
  • By about 30,000 years ago, anatomically modern humans were the only members of genus Homo remaining, excluding small, isolated populations.
• Recent fossil finds and extensive molecular analyses have promoted the (recent) out-of-Africa model as the main explanation for the origin of modern humans living around the world.
  • New data include the discovery of the earliest fossilized remains of modern H. sapiens in Africa and analyses of DNA from mitochondria, the Y chromosome, and autosomes.

\

Cultural Change

• Large human brain size makes possible the transmission of knowledge from one generation to the next.
  • Significant advances in human culture were the transition from a hunter– gatherer way of life to the development of agriculture and the Industrial Revolution.

\