Population Genetics 3 - Human Origins and Evolution

Human origins: Homo

Homo habilis    2.3 Mya

                           communal living in caves

                           cared for young

Homo erectus  15,000-750,000 years ago

                           angled skull, possible speech

                           social, cooperative, tool-using

                           male-female pairs

Neanderthals    28,000-150,000 years ago

                           larger brains, prominent brow arches

                           muscular jaws, distinct spacing of teeth

                           large, barrel-shaped chests

Cro-Magnon     communal,

                           jewelry, intricate cave art

Homo sapiens  from 40,000 years ago-

                                       migration from Africa, 10,000 years ago

Molecular Evolution

   Study of evolution through comparison of DNA sequences, chromosome banding and genome structure.

Mutations occur in DNA over time.

Comparing two DNA sequences

•   fewer changes => closer relation 

                                      more recent divergence

•   more changes => more ancient divergence

Molecular Evolution: comparing genomes

   Humans, chimps, and bonobos share 99.5% of their genes encoding proteins.

Traits defining “humanness” may be rare.

Molecular Evolution: comparing chromosomes

    Human chromosomes banding is highly conserved between humans and the other great apes.

Molecular Evolution:  comparing protein sequences

Comparison of DNA sequences indicates degree of evolutionary relation

Ancient DNA has been isolated from a few well preserved fossils

Human migration out of Africa

Out of Africa or replacement hypothesis

•Within Africa, Homo sapiens evolved from Homo erectus. 

•Descendants migrated from Africa to replace hominids living in Europe, Asia and Middle East.

Multiregional hypothesis

•Homo erectus migrated out of Africa to Europe, Asia and Middle East. 

•Evolution of Homo sapiens occurred in multiple locations with interbreeding between populations.

Mitochondrial “Eve”

•mtDNA sequences of indigenous peoples worldwide were compared to determine the common ancestral mtDNA sequence.

•Root of tree is in Africa

•Calibration of molecular clock with chimp outgroups indicate the common ancestral sequence existed 100,000 to 300,000 years ago.

DNA sequence comparisons of Asian and Native American populations

Anthropologists hypothesize three migrations to

North America from Siberia to explain language and

cultural distinctions in Native American

populations.

Migration across the Bering strait

Eugenics

    Is a social movement advocating control of individual reproductive choices to change society

   Sir Francis Galton, 1883, coined the term eugenics meaning “good in birth”

   “The science of improvement of the human race germ-plasm through better breeding”