• Humans resemble African apes, so they originated in Africa

• Intelligence is important for hunting and the human terrestrial adaptation

• Bipedalism evolved to free the hands for carrying weapons

• Canines reduced as weapons replaced them for defense

Anatomical evidence for it: T H Huxley’s Man’s Place in Nature (“Darwin’s bulldog”)

Arguments Against African Origin

• Gorillas and chimps too specialized

• Haeckel (“German Darwin”): general ape ancestor like gibbon

-Inspires Dubois to search Java

• Placed too much emphasis on basic primate features of humans

• Expected early African apes to be identical to modern forms

• No fossil evidence in Asia

• African fossils

• DNA analysis confirms Darwin

• Intelligence, seen in a big brain, needed for hunting and the terrestrial life

• Why was a large brain so important for hominin origins?

-Modern humans have one

-Thought to be most important human feature, so must have great antiquity

• Expectation of large brain fuels acceptance of Piltdown: large brain & primitive jaw

-Taung Australopith, 1925 

• Rejected by many because brain was small, ape-sized

Darts’ Killer Ape Hypothesis – modeled after Darwin

-Dart and the ODK Industry -Osteodontokeratic, bone-teeth-horn tools, actually just broken bones etc.

-Louis Leakey and habilis -Idea that stone tool maker had bigger brain

-Lucy discovery in 1970’s w/an associated cranium and postcrania -demonstrates that bipedalism preceded brain expansion.

• Need for ‘fuel’ to maintain so much brain tissue is the driving force behind hunting and the consumption of animal protein

• Only relevant for hominin origins if large brain is developed from the beginning

• However, the expensive brain hypothesis may have some merit

• It may have been a reliance upon high energy, hard to eat foods that allowed brain development (fallback?)

• This has the advantage of also explaining changes in human dentition and the robust australopiths, but does not explain bipedalism

• Why did it develop?

• Darwin said to free the hands for tools (weapons)

-Weapons, tools, food or kids?

• Were hands useful for carrying items over long distance to provision the rest of the group?

• Apes occasionally DO walk bipedally when their hands are full..

• This may have allowed hominins to move out of forests grab high energy foods (such as tubers) and retreat back to the trees for safety..provisioning young in safe place

• Shift to more mobile lifestyle makes carrying infants difficult; hair loss?

• Did bipedalism free up the hands to carry infants over distances?

• It seems more likely that infants could be left somewhere and provisioned

• Bipedalism helps cool off the head and the body- less surface area hit by the sun

• Might be good in hot savannahs

• Blood drain coming down from head might have had a “radiator” effect, allowing for less overheating and expansion of brain

• Studies of chimp locomotion indicate that knuckle walking/ape bipedalism are very energy inefficient

• Human bipedalism is much better at energy conservation and could allow for better range and collection of resources

• Darwin: weapons in hands instead of the mouth

• But changes are not just with canines

Social Control Model

• Changes in hominin dentition as male behavior is modified by group social constraints

Less agression/competion

=less need for big canines?

Man the Hunter vs. Woman the Gatherer

• The Seed-Eaters: A New Model of Hominid Differentiation Based on a Baboon Analogy

• Hominins adapted to eat seeds like geladas

• Postural model

• African origins still upheld

• Large brain and hunting lifeway widely accepted part of the model (even today), but shifted to Homo origins- correlation between Homo & stone tools

• But: Tools and other behaviors more important than weapons for bipedalism?

• Dietary adaptations rather than weaponry

• 1980’s model

• Demographic shift critical to hominin origins

• Shortening of birth spacing

• Dependent, altricial young & orphaning

• Solution: monogamy & male provisioning

• Shift in female roles in solving the demographic dilemma

• Groups of related female kin as most likely social grouping for care demands; older females?

• Motherese and language development