Human Evolution
February 25
Rise of the genus homo
Species in the genus: homo: habilis; rudolfensis; erectus; ergaster; heidelbergensis; antecessor; neanderthalensis; floresiensis; sapiens (us)
- First evolved in Africa; most date 2.4-1.8 MYA; first fossil member is Homo habilis (handy man); named such due to possible stone tools discovered nearby; some suggest H. habilis is actually multiple species
Homo Habilis [Tanzania, Kenya, and Ethiopia (2.3-1.6 MYA)]
- Species designation - brain size and association with stone tools
- Skeletal morphology similar to contemporaneous australopithecines
- May represent 2 or more different species (H. rudolfensis & H. habilis)
Homo rudolfensis: Koobi Fora, Kenya
- Originally considered H. habilis
- Does H. rudolfensis or H. habilis first representative of our genus? Very controversial (since many specimens are highly fractured
Homo Erectus [Asia and Southeast Asia 1.8 MYA – 27 KYA]
- First species in genus homo found outside Africa
- Brain and body size changes in lineage
- Controlled use of fire and hunting; early African specimens may be different species, Homo ergaster
Homo ergaster: East and South Africa; 1.8 – 1.3 MYA
- Distinguished from H. erectus by thinner skull-bones & lack of an obvious supraorbital foramen(眶上孔)
- Debate on H. ergaster or H. erectus as direct ancestor of modern humans
Homo heidelbergensis: Europe and Africa; 700 – 130 KYA
- Compared to H. erectus, H. heidelbergensis has smaller dentition, larger brain size, and larger body size
Homo antecessor: Spain; 1.2 MYA – 800 KYA
- Controversy surrounding species designation; type specimen is juvenile
- 1st hominin in Europe?
Homo neanderthalensis: Europe and Middle East (300 – 35 KYA)
- Limb bones heavily marked by muscular attachments
- Thick walls of cortical bone & large joints
- Neanderthals extremely muscular, highly active, & athletic by modern human standards; Neanderthals made stone tools, used fire, and were hunters
- Geneticists able to extract DNA from 3 Neanderthal specimens
- Early studies: Genetics of Neanderthals vs modern humans point to a 706 KYA separation & considerable variation
- Recent studies: Half of Neanderthal genome; demonstrated a range of genetic contribution to non-African modern humans of 1% to 4%, likely in Levant (Middle East); VERY CONTROVERSIAL!
Homo naledi: discovered 2013 in South Africa; not dated as yet
- Body mass and stature = small-bodied human populations
- Endocranial(颅内膜) volume similar to Australopithecus; skull shape similar to early Homo species
- Skeleton combines primitive features in australopithecines with features known from hominids
Homo floresiensis: Flores Island, Indonesia; 95 – 13 KYA
- Small body size (ca. 1.06 m); small brain size; primitive and derived features
- NOT aberrant individual; rather, unique species
Homo sapiens: ca. 160 KYA in Africaca. 100 KYA in Middle East, and ca. 40 KYA in Europe
- Controlled use of fire; hunting and gathering; cultural remains
- Increasingly complex stone tools
Human Origins
Hypothesis
- Replacement Hypothesis: one wave of human dispersal and replacement of other congenera(先天) out of Africa; modern humans are descendants of African H. sapiens
- H. neanderthalensis is evolutionary dead end
- Multiregional Hypothesis: no wave of H. sapiens replacements; H. erectus most recent common ancestor of modern humans
- H. neanderthalensis contributed to gene pool of some modern human populations
Analysis of multiple human genes reveals patterns of recurrent gene flow
-
Denisova hominin [Denisova Cave: In Russia]
- Russian archaeologists found finger bone of juvenile hominin (X woman) & tooth from young male about 41 KYA; mtDNA (bone) and nuclear DNA (tooth analysis) indicated that: Modern Humans, Neanderthals, and Denisova hominin last shared common ancestor around 390 KYA
- Denisovans actually a sister group to Neanderthals; Denisovans lived among and interbred with the ancestors of some modern humans in Southeast Asia
-
DNA Evidence of Admixture: identified DNA inherited from multiple archaic hominin ancestors and applied it to 1523 geographically diverse individuals, including 35 new Island Melanesian genomes
- Indicating ancestors of modern humans interbred with Neanderthals and Denisovans at least four times in course of prehistory;
- Interbreeding may have given modern humans genes that bolstered immunity to pathogens
-
Direct Evidence of Admixture: genome of Denisova 11; a bone fragment from 13-year-old girl from Denisova Cave, comes from an individual who had a Neanderthal mother and a Denisovan father
- Likely migration of Neanderthals between eastern & western Eurasia occurred after 120 KYA
Human variation (race)
- Race (science) - a geographically circumscribed(外接的) population or set of populations that differ from all other populations of a species
- Race (biology) - synonymous with subspecies (geographically isolated populations within species)
Racial Bundles
- “White” bundle: pale skin; straight or wavy hair; noses of narrow to medium width; medium to tall stature
- “Black” bundle: black or dark brown skin; wiry hair; thick noses and lips; medium stature
Skin Colour Adaptation
- Physical traits have broad distributions, rather than being clustered in a particular area
- Dark brown skin is found in Sub-Saharan Africans as well as people from Southern Asia, Australia, New Guinea and on nearby islands of Melanesia, as well as in much of the Americas
- Produced by melanin in epidermis
- ==Melanin== - primary determinant of human skin colour and also found in hair and other body parts; melanin provides ultraviolet radiation protection, nutrient protection, Vitamin D synthesis
- “Racial” Abilities: not an idea supported by anthropologists; lack of scientific support
Are there human races?
No biological or phylogenetic ways to define a human race; race concepts based on everything from skin colour through region(s) of origin to ethnicity; crude classification system typically involves self-identification based on up-bringing, culture, ethnicity etc.; morphological and genetic differences in human “races” much smaller than those needed to consider nonhuman animals subspecies;
**Conclusion: no human races