Human Evolution The beginning 10 million years ago

Human Evolution The beginning: 10 million years ago in Africa Climatic change. Getting drier. Unbroken tropical forests becoming a patchwork of woodland 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 6 mybp • 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. 5 mybp, est. 4 yrs. Period of nutritional stress at 2. 5 yrs, 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 51 mybp, 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 (640 cc; note chimps are about 400 cc). Evidence of simple stone tools found also. • Homo rudolfensis: 1970’s Richard Leakey. Brain size 750 cc, 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. 6 mybp • 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.