Human EvolutionThe beginning: 10 million years ago in Africa

Climatic change. Getting drier. Unbroken tropical forests becoming a patchwork of woodland and savanna.

The split

• Sometime around 7 mybp east African primates began on an evolutionary path distinct from central and west African primates.

• West was more densely wooded. East less so, more open. East African primates went bipedal. Why? We don’t know– Carrying babies?– Making tools?– Thermodymics?– Wading along shorelines?– Looking for predators?– More efficient movement?

Earliest hominins: pre-Australopiths•Sahelanthropus tchadensis. (Toumai, “hope of life” in Goran). A single skull, jaw fragments, several teeth, unearthed in 2002 by Michael Brunet, dated to about 6.5

mybp Found in Chad, central Africa? •Forward position of foramen magnum suggest bipedalism

Earliest hominins: pre-Australopiths• Orrorin tugenenis “original man” in the local Tugen

language. February 2001, French researcher Brigitte Senut, a few teeth and limb bone fragments in the Tugen hills of Kenya, dated to about 6mybp

• Femur angle suggests bipedalism

Earliest hominins: pre-Australopiths

• Ardipithecus kadabba found in the Middle Awash region of Ethiopia, dated to around 5.5 mybp

• Ardipithecus ramidus (Ardi) remains are dated to between 5-4.4 mybp; forest-dwelling, bipedal, but at home in trees as well. No evidence of knuckle-walking; is this derived feature in great apes?

• Contros: – Are kadabba and ramidus related? – Are kadabba, orrorin, and sahelanthropus related?– Ardi appears to have low sexual size dimorphism,

but australopiths have traditionally been thought of as highly dimorphic species?

– Is Ardi the only one likely to be ancestral to Homo?

Earliest hominins: Australopiths

• Australopithecus anamensis, first uncovered in 1995 in northern Kenya and dated to between 4.2 and 3.9 mybp.

• Australopithecus afarensis (Lucy) found in the mid-1970’s by Donald Johanson and dated to around 3.3 mybp

• Australopithecus africanus, Tung child found by Raymond Dart of the University of Witwatersrand in South Africa, 1922. Dated as somewhat more recent than Lucy

Earliest hominins: Australopiths

• Lucy bones – unquestionably bipedal. Some adaptations for tree-dwelling present. Small 3-4 feet in stature. High sexual dimorphism. Probably didn’t run very well. Ate fruits, nuts, insects, small USOs, amounts of meat. Was prey as much as predator.

Earliest hominins: Australopiths

• Dart’s Taung child, killed by predator? Dated at about 2.5mybp, est. 4yrs.

• Period of nutritional stress at 2.5yrs, possible early weaning age compared to apes; evidence of cooperative breeding, care of young?

Earliest hominins: Australopiths

• The pitted pattern of Laetoli feet, about 3.5 mybp.

Earliest hominins: Australopiths

• Two general types: • Gracile: Thinner boned, less powerful jaws, probably ate more

fruits, insects, etc. (ex. Africanus, afarensis)• Robust: thicker boned, more powerful jaws, ridge crest on cranium,

flatter teeth, seed-crusher, fibrous vegetable material (probably not human ancestor; ex: Australopithicus or Paranthropus boisei and A. or P. aethiopicus)

Earliest hominins: Australopiths

Summary: Time period 5-1mybp, robust later than gracile. Robusts may have made stone tools, but little evidence. High sexual dimorphism, male – male competition. Small family – female bonded groups, single male. Bipedal but well adapted to trees. Forest, waterside dweller. Chimp-size brain, robust a little larger. Probably restricted to Africa. Bipedal apes.

Early Homo

• Homo habilis: Unearthed 1960’s Louis Leakey. Olduvai Gorge in northern Tanzania. Larger brain size (640cc; note chimps are about 400cc). Evidence of simple stone tools found also.

• Homo rudolfensis: 1970’s Richard Leakey. Brain size 750cc, but with more primitive looking face. Both dated to around 2.3-2.0 mybp

The Oldowan tool kit• Simple stone tools made by striking a

hammer stone against a core to make a shape flake (cores may also have been used occasionally as tools). 2.6mybp

• Probably used for butchery, scrapping, cutting, smashing

Hand/Brain and tool manufacture

Pad to side grip: thumb to side of index finger

Three jawed chuck grip: thumb, index, middle finger (baseball grip)

Five jawed cradle: thumb against four fingers

Lucy could use these grips, apes generally cannot. Pounding, digging (USOs), throwing. Oldowan tools probably not, but maybe robusts later.

What Lucy could not do:

Oblique power grip: fourth and fifth fingers in ulnar opposition to thumb, used for holding and swinging clubs and hammers

Hand/Brain and tool manufacture

• Pet scans of Oldowan knapping: visual-motor coordination

• Primary motor cortex• Somatosensory cortex• Dorsal visual pathway

(occipital/superior partietal)• Cerrebellum• Little frontal lobe activation

Knapping apes

• Kanzi knapping studies• Produces “oldowan-like” tools, but not using percussion

technique• Less power; less precision and selectivity

• Percussion technique requires motor control beyond that of nonhuman apes. Some advance in planning perceptual motor skills.

• Some evidence of adjustment in ongoing flaking process (Lokalalei site, northern Keyna)

• Probably not a big cognitive advance.