Human Evolution

Paleoanthropology = The study of human origins and evolution.

Primates have been present for 65 million years (end of Mesozoic era) and are defined by characteristics shaped by natural selection for living in trees. Later, this selection pressure will change. A diagram of probable primate evolution. Fig. 27.2

- Limber shoulder joints which make it possible to brachiate. Movie of brachiation!

- Dexterous hands for hanging on branches and manipulating food.

- Sensitive fingers with nails, not claws.

- Opposable thumb and 4 fingers.

- Eyes are close together on the front of the face, giving overlapping fields of vision for  enhanced depth perception (binocular vision). Fig 34.40

- Excellent eye-hand coordination.

- Parental care with usually single births and long nurturing of offspring.

- Poor sense of smell

Prosimians Fig 27.1 (non-anthropoid primates) For images of lemurs, lorises, etc.

The anthropoids include all other primates.

- Fossils of monkey-like primates indicate anthropoids were established in Africa and Asia by 45 million years ago (S. Amer. and Africa were separated)

- Primates became diurnal about 36 million years ago

- Refinement of opposable thumb

    - The New World monkeys, (images) some with prehensile tails (Fig 27.3)

    - The Old World monkeys (images)

Hominoids: hominids plus apes (Fig 34.37)

Hominids: humans and their direct ancestors

Homo sapiens is the only living hominid.

Evolutionary Origins of Humans. 5-8 mya

Trends in hominid evolution

- the location of the foramen magnum (where the spinal cord enters the skull).

- shape of the pelvis

- curvature of the spine

- first toe opposable or not

- Laetoli footprints in Tanzania (Fig. 27.8 and Image) (about 3.5 MY old) support the conclusion of early bipedalism. Fig. 27.7.

Hominids walked upright for two million years without a substantial increase in brain size. It is a common misconception that all traits evolved at the same time.

This link will take you to a page that has a paragraph or 2 about each of these species.

Fig 27.9 gives approximate time lines for some of these species.  Talk Origins timeline.

Map of Africa.

Sahelanthropus tchadensis ­ discovered in 2001 in Chad - between 6 and 7 myo. Not certain if it is a hominid or more kin to apes. Face much flatter but not certain at this point if it was fully bipedal. Significant also because found much further west in Africa than any other hominid fossil. See an article and links here and here. See a website on this species here. And an article.

Orrorin tugenensis (about 6 mya)

Ardipithecus ramidus (Australopithecus ramidus) (4.4 - 4.2 mya). Fossil.

Australopithecines: (southern ape) Figs 27.6a and 27.6b. The First Humans: 4.4 - 1.1 mya. Map of eastern Africa and sites of fossil finds. Map with skulls.

Australopithecus anamensis. (4.2 - 3.9 myo). Jaw.

Australopithecus afarensis. (3.7 - 2.8 myo) "Lucy" about 3.2 myo. Skull. Found in Ethiopia in Afar region in 1974. Skeleton (Image)

Kenyanthropus platyops (3.5 myo). It lived about the same time as A. afarensis, but has a flatter face and smaller teeth, appearing more similar to modern humans than did A. afarensis. The skull was found on the shores of Lake Turkana in Kenya. More information here and here.

Australopithecus africanus (3 - 2 myo). Skull. First hominid fossil found.

Australopithecus afarensis and africanus are known as gracile australopithecines

Australopithecus garhi (2.5 myo) - possibly first tool user. Found in Ethiopia with shaped tools. Skull.

Australopithecus boisei (2.3 - 1.4 myo). Skull.

Australopithecus robustus (1.9 - 1.5 myo). Skull.

Australopithecus robustus and boisei are known as robust australopithecines.

Gracile vs robust skulls. And here.

Homo spp. 2.4 myo to present. Significantly larger brain size than australopithecines. Figs. 27.12a and 27.12b

Homo habilis "handy man" (2.5 - 1.6 myo). Skull. Once thought to be the first tool user. Broca's area developed.

Homo rudolfensis (2.4-1.8 myo). Skull. May be larger habilis.

Homo ergaster ­ Fig. 27.10. similar to Homo habilis but larger.

Homo erectus (1.8 myo to perhaps 250,000 years ago). First with evidence that they used fire. Replica of skull. Another skull.

Homo floresiensis (95,000 and 13,000 years ago) National Geographic article and the Nature article.

Homo heidelbergensis (800,000 - 100,000 years ago) - may have led to sapiens or neandertalensis.

Homo neanderthalensis (some consider as Homo sapiens neanderthalensis) (230,000 - 30,000 years ago) Neanderthals. Skull.  Neanderthals versus sapiens.

Homo sapiens (modern) (100,000 years ago to present). Skull.

         Cro-Magnon - More info here

The Multiregional Hypothesis

The Out-of-Africa or Replacement Hypothesis (Fig 27.13)

This image compares these two models.

Cultural evolution - See some prehistoric art here. And here.

Tools

Agriculture began about 8,000 BC in the fertile valley of Mesopotamia.

Links:

The primates

Talk Origins

Becoming human