Topic 20 - Human Evolution

Why are Humas Subject to the Laws of Natural Selection?

Humans are living and therefore must live by the laws of natural selection.

What are the Derived Characteristics that Humans and Great Apes share?

• relatively large brains

• no tail

• increased flexibility of the thumb

• more erect posture

What traits are most likely Present in the Last Common Ancestor of Chimps and Humans?

• knuckle walker

• fruit diet

• large flat molars / pre-molars

• variety of habitat types

• culture

• phenotypically flexible

What was the pattern of Evolution from Pan to Homo?

• Earliest hominin fossil (Sahelanthropus tchadensis) is about 6-7 mya

• Earliest hominin fossil (Orrorin tugenensis) is about 6 mya

• 6 gracile hominins about 4-2.5 mya show that they had small braincases, large projecting faces, small stature and were bipedal

• 3 robust hominins about 2.7 mya had all of the characteristics of before, except they now have large cheek teeth, robust jaws, strong jaw muscles, and a sagittal crest

• first appearance of Homo about 2.4-1.6 mya show that they had a large braincase, smaller, flatter face, smaller teeth and jaws, taller, and longer legs

• Australopithecus sediba about 1.95-1.78 mya

• 4 species of Homo (including us) about 1.2 - present mya show that they had even larger braincases, high steep forehead, short, flat, vertical face, and a prominent nose

• Homo naledi about 335-236 thya

• Denisovans about 300-30 thya (similar to Neanderthals’)

• Homo juluensis about 300-50 thya (similar to Neanderthals)

• Homo luzonensis about 67-50 thya

• Homo floresiensis about 39-12 thya

4 Models of the Origin of Homo sapiens

1. African replacement

   • we evolved in Africa

   • migrated to Europe and Asia

   • outcompeted H.erectus and H.neaderthalensis

2. Candelabra model

   • H.sapiens evolved independently in Africa, Europe and Asia

   • No gene flow between populations

   • not very likely

3. Hybridization and assimilation model

   • H.sapiens evolved in Africa

   • migrated to Europe and Asia

   • replaced local populations of H.erectus and H.neaderthalensis through hybridization

4. Multiregional model

   • H.sapiens evolved concurrently in Africa, Europe, and Asia

   • sufficient gene flow to maintain continuity as a single species

The most accurate model is between the African replacement Multiregional model.

What are Uniquely Human Traits?

• Bipedalism

• large brains

• an ability make and use complex tools

• ability to use language