Major Primate Groups Lemurs Tarsiiformes New World Monkeys Old World Monkeys Gibbons Orangutan Gorilla Chimp Human Family Hominidae 25 mya 12 mya 6 mya Hasegawa et al mya 38 mya Estimated Divergence Times

What Traits Do Humans and Apes Share? Larger Brain Absence of a tail More erect posture Greater flexibility of hips, ankles, wrist, thumb DNA sequence similarity

Gorilla Chimpanzee Human Horai et al (1995) Proc. Nat Acad Sci. 92: Mito DNA (complete sequences) Kim and Takenaka (1996) A. J. Phys. Anth. 100: Y-chromosome DNA Ruvolo (1997) Mol Biol Evol 10: Examined 14 different DNA data sets Satta et al (2000) Mol. Phyl. Evol 14: Autosomal DNA (45 genes, 47,000 bp of DNA)

Common Ancestor of Chimp/Human Knuckle-walker Broad-fruit based diet May have hunted May have used tools May have had complex social relationships: (e.g.warfare, cannabalism, sharing, teaching, compassion)

Our Understanding of Human Evolution is Primarily Based on Fossils Gracile Australopithecines

Chimp / Human Split Fossil Evidence Indicates Two Primary Hominid Groups

Australopithecus/Paranthropus 4.1 mya to 1.2 mya Bipedal –Foramen magnum faces down – 3.6 my footprints found in volcanic ash near afarensis fossil Large projecting face, small brain case (400 cm 3 ) Small in stature (3’7’’ - 4’11’’ ft) Two distinct lineages (gracile and robust) May have developed tools

Chimp / Human Split Homo is thought to have evolved from A. afarensis

Homo 1.9 mya to present Larger braincases (cro-magnon: 1600 cm 3 ) than australopithecines and smaller face Smaller jaws and teeth Much taller than australopithecines Development of tools, culture, and language

Trends in Homo Evolution Increase in brain volume Increase in size Skull evolution : vertical face, smaller jaw, round forehead Bipedalism Tool development Cultural development

Slight Increase In Body Size Much Greater Increase In Brain Volume

Braincase Volume and Body Mass

Early Tools

These species are associated with manufactured stone tools. Evidence that P. robustus used tools Susman, 1994 Paranthropus robustus

Is Language a Recently Evolved Trait Unique to Homo sapiens? Earliest cave paintings are 32,000 yrs old. Neural circuits of the brain associated with language (Broca’s area and Wernicke’s area) are enlarged in H. habilis. The neandertal hyoid of the larynx is exactly like our hyoid.

Hyoid Bone Chimp Larynx Hyoid Bone Neandertal Larynx

Summary of Hominid Evolution Since the Chimp/Human Common Ancestor Frequent speciation produced a diversity of species As many as 5 different species may have coexisted at one time We are the lone survivors of an otherwise extinct radiation of bipedal African hominids

What is the Origin of Modern Human Populations? Multiregional Hypothesis –Homo sapiens evolved from an ancient stock of Homo erectus that originated in Africa (~ mya) Out of Africa Hypothesis –Homo sapiens evolved from a relatively recent stock of archaic sapiens that originated in Africa (~ ,000 ya)

Chimp / Human Split

Multiregional Hypothesis –Predicts that Homo sapien “eve” existed more than 1 mya. Out of Africa Hypothesis –Predicts that Homo sapien “eve” existed ~ 200,000 yr ago. How Can We Test These Hypotheses With Molecular Data?

Molecular Clock Estimate of Divergence Time of Modern Humans GeneEstimateReference mt DNA ,000 Vigilant et al., 1991 mt DNA ,000 Ruvolo et al., 1993 nuclear DNA ,000Bowcock et al., 1994 mt DNA ,000Horai et al., 1995 nuclear DNA ,000Tishkoff et al., 1996

Overall, Out of Africa is Supported by the Majority of the Evidence “In each great region of the world the living mammals are closely related to the extinct species of the same region. It is, therefore, probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee; And as these two species are now man’s nearest allies, It is somewhat more probable that our early progenitors lived on the African continent than elsewhere.” Charles Darwin The Descent of Man, 1871