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Evolution of Hominids: From Hominoids to Hominins

Explore the origins of hominids, from hominoids to hominins, key discoveries, climate change impact, shared traits, and major findings in bioanthropology. Discover the evolution of bipedalism and early hominin species.

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Evolution of Hominids: From Hominoids to Hominins

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  1. ANG 6930Proseminar in Anthropology IIA: Bioanthropology Day 5 ANG 6930 Prof. Connie J. Mulligan Department of Anthropology

  2. This week • Hominoid to hominin • Dating the ape-human split • Australopiths • Early hominin subsistence and social organization • Origins of genus Homo • Homo erectus • Neanderthals and other archaic humans • Reading • The Human Species, Chpts 9 (Primate origins and evolution), 10 (Beginnings of human evolution), 11 (Origin/evolution of genus Homo) • Course packet • “A new kind of ancestor: Ardipithecus unveiled”, Science, 326:36-40. • “Candidate human ancestor from South Africa sparks praise and debate”, Science • Klein RG. 2009. Darwin and the recent African origin of modern humans. PNAS 106:16007-16009. • “New statistical model moves human evolution back three million years” ScienceDaily, 11/9/2010. • Teaford MR and Ungar PS. 2000. Diet and the evolution of the earliest human ancestors. PNAS 97:13506-13511. • Conroy GC. 2002. Speciosity in the early Homo lineage: Too many, too few, or just about right? Journal of Human Evolution 43:759-766. • Premo LS and Hublin J-J. 2009. Culture, population structure, and low genetic diversity in Pleistocene hominins. PNAS 106:33-37. • Hublin JJ. 2009. The origin of Neanderthals. PNAS 106:16022-16027. • “Tales of a prehistoric human genome” Science 2009, 323:866-871. • Optional– Noonan JP. Neanderthal genomics and the evolution of modern humans.

  3. Next week • Origin of modern humans/Human biodiversity and race • Homo floresiensis • Anatomically modern Homo sapiens • African replacement or multiregional evolution? • Global patterns of human genetic variation • Anthropological critique of race • Reading • The Human Species, Chpts 12 (Origin of modern humans), 13 (Human variation), 14 (Genetics, history and ancestry) • Course packet • Tattersall I. 2009. Human origins: Out of Africa. Proceedings of the National Academy of Sciences 106:16018-16021. • Powledge TM. 2006. What is the Hobbit? PLoS Biology. 4:2186-2189. • Scheinfeldt L et al. 2010. Working toward a synthesis of archaeological, linguistic, and genetic data for inferring African population history. Proceedings of the National Academy of Sciences 107:8931-8938. • Serre D and Pääbo S. 2004. Evidence for gradients of human genetic diversity within and among continents. Genome Research 14:1679-1685. • Haak W. 2008. Ancient DNA, strontium isotopes, and osteological analyses shed light on social and kinship organization of the Later Stone Age. PNAS. 105:18226-18231. • “On the origin of art and symbolism” Science 2009, 323:709-711.

  4. Hominoid to Hominin

  5. Overview • Origin of hominins in late Miocene • Ardipithecus • Orrorin • Sahelanthropus • Plio-pleistocene hominin adaptive radiation • Australopithecus • Paranthropus • Kenyanthropus • Hominin phylogenies • Evolution of bipedalism

  6. Overview of hominid evolution

  7. Climate change in late Miocene/PlioceneHominids evolved ~6 mill yrs ago

  8. Late Miocene to Early Pliocene • Apes flourished in Miocene, but most genera became extinct • Falling temperatures changed climate in African tropics • Rain fall declined, became more seasonal • Tropical forests shrank; woodlands, grasslands expanded • Ecological pressures led to evolution of first hominids about 6-8 mya

  9. What makes a hominid? • Human uniqueness long defined in terms of brain evolution • Now clear that bipedalism predates big brains by several million years • Bipedalism associated with morphological changes • Dietary changes associated with new habitats, also reflected in different chewing apparatus

  10. Shared, derived traits of hominids • Habitual bipedalism • Chewing apparatus • Wide parabolic dental arcade • Thick enamel • Reduced canines • Larger molars in relation to other teeth • Much larger brains relative to body size • Slow development with long juvenile period • Elaborate, highly variable material and symbolic culture, transmitted in part through spoken language

  11. Major discoveries of hominidsMainly South Africa and East Africa

  12. New discoveries of hominids 5-7 mya • (Ardipithecus ramidus • 1992 • Middle Awash in Ethiopia • Previously thought to be older than 5 mya, now 4.4 mya) • Orrorin tugenensis • 2001 • Tugen Hills in Kenya • Sahelanthropus tchadensis • 2002 • Toros-Menalla in Chad • Ardipithecus kadabba • 2004 • Middle Awash in Ethiopia

  13. Sahelanthropus tchadensis • Discovered in 2002 by Michel Brunet and colleagues • New dental and mandibular specimens reported in 2005 • Estimated 6-7 mya in Chad, not securely dated • Fits with humans if older human-chimp divergence is used • Unique mix of humanlike and apelike features • Relatively flat face and massive brow ridge • Small brain, primitive teeth, back of skull very apelike • No postcranial fossils known • Could be hominoid, not hominid Toumaï

  14. Orrorin tugenensis • Announced in 2001 by Senut and Pickford • 6 mya at Tugen Hills in Kenya • No cranial fossils recovered • Keep controversy alive (could be ardipithecus) • Mixture of apelike-humanlike • Incisors, canines, premolars, arm and fingers like chimpanzees • Thick enamel, femur humanlike • Bipedalism inferred from femur anatomy

  15. Ardipithecus kadabba 1st designated as subspecies, then promoted to full species in 2004 Even older - 5.8 – 5.2 Ma Ethiopia (Middle Awash) Similar to Sahelanthropus in mix of features Slightly smaller Canine Wooded habitat Yohannes Haile-Selassie

  16. Ardipithecus ramidusFirst identified and named in 1994 – thought to be older than 5 mya15 years to excavate >100 fragments and reassemble them, e.g. >1000 hours on skull (Gen Suwa) – 4.4 mya Nature 371: 306-312 (1994)

  17. Ardipithecus ramidus – “ARDI” 4.4 mya Discovered in Middle Awash – Aramis (Ethiopia) Most complete skeleton older than Lucy Not Homo and not Australopithecus Similarities to Sahelanthropus Very early stage of human evolution

  18. Unexpected anatomy White, Gibbons (2009) A new kind of ancestor: Ardipithecus unveiled. Science

  19. White, Gibbons (2009) A new kind of ancestor: Ardipithecus unveiled. Science

  20. Significance of late Miocene hominids • Pushes back fossil record of hominids by 2-3 million years • Until early 1990s, earliest hominids were < 4 mya • Now appears that multiple, diverse hominids may date to late Miocene • Forces rethinking of bipedalism • Early hominids appear to have inhabited forested environments, not open savannas • Challenges some scenarios for adaptive value of bipedalism • Having hand free to use tools doesn’t seem important since bipedalism predates tool use by 3.5 my

  21. Diversification of hominids • Hominid lineage proliferated 4–2 mya, likely with multiple species living in Africa at a time • Taxonomic classification of these hominids hotly contested • Lumpers and splitters • Linear and bushy family trees • Bernard Wood and Mark Collard advocate three genera • Australopithecus, Paranthropus, Kenyanthropus

  22. Australopithecus • Debate about how many species belong to genus • Two major points of disagreement • Robust australopithecines • Early Homo • Wood and Collard’s scheme narrows definition of Australopithecus and of Homo • Taxonomic debates reflect limitations of data, philosophical differences, and politics

  23. Primitive and later hominids • Primitive hominids • Australopithecus anamensis • Australopithecus afarensis • Kenyanthropus platyops • Later hominids • Paranthropus or robust Australopithecus • Australopithecus africanus • Australopithecus garhi • Australopithecus habilis, A. rudolfensis

  24. Australopithecus anamensis • Earliest species of genus to be found • Dated to 4.2-3.8 mya near Lake Turkana in Kenya (Leakey et al. 1995, 1998) • Bipedalism inferred from knee and ankle joints • Thick enamel and smaller canines • Arm bone suggests primitive arboreal adaptations • Dental arcade and chin chimpanzee-like • Primitive characters suggest A. anamensis may be ancestral to later australopithecines

  25. Australopithecus afarensis • Most well-known australopithecine = Lucy • Most complete skeleton (40%) • Dates to 3.5-2.3 mya in East Africa (Don Johanson, 1970s) • Bipedalism • Shape of pelvis, femur, foot, Laetoli footprints • May not have been fully modern gait • Derived characters intermediate between humans and chimps • Dental arcade • Canines • Premolar cusps

  26. Laetoli footprints • Formed and preserved by a chance combination of events -- a volcanic eruption, a rainstorm, and another ashfall • Tanzania • Two individuals, possibly three • Fainter of two clear trails is unbalanced, individual possibly burdened on one side w/ an infant? • A. afarensis • No other hominid near this age, 3.6 mya

  27. Kenyanthropus platyops • Dated to 3.5-3.2 mya on western side of Lake Turkana (Leakey et al. 2001) • Mosaic of features • Small ear hole (like early Australopithecus) • Thick enamel (like later Australopithecus) • Relatively flat face (like later hominids) • Apart from brain size, is similar to Homo rudolfensis KNM-WT 40000

  28. Robust hominids • Robust early hominids have crania and teeth specialized for heavy chewing • Sagittal crest • Flared zygomatic arches • Massive mandibles and molars • Debate over proper genus (Australopithecus or Paranthropus) • Paranthropus aethiopicus • Paranthropus robustus • Paranthropus boisei KNM-ER 17000

  29. Who became Homo? • General agreement that the robust australopithecines became extinct ~1 mya and did not give rise to modern humans • Who did? • Three major candidates • Australopithecus africanus • Australopithecus garhi • Australopithecus sebida

  30. Australopithecus africanus • First known australopithecine (Dart 1925) • Dated to 3-2.2 mya in South Africa • More apelike physique than A. afarensis • Arms longer than legs – arboreality • Some adaptations for heavy chewing • Probably like other australopiths, matured rapidly like chimpanzees • One candidate for immediate ancestor to Homo Taung Child

  31. Australopithecus garhi • Dated to around 2.5 mya in East Africa (Asfaw et al. 1999) • Small brains like A. afarensis and A. africanus • Very prognathic face, larger teeth, sagittal crest • Some evidence that made stone tools and used to cut meat from bones, extract marrow • Other candidate for immediate ancestor to Homo BOU-VP-12/130

  32. Known dates for hominid species

  33. Hominid phylogenies Gibbons, Ann. 2002. "In Search of the First Hominids." Science 295:1214-1219.

  34. Science online extras

  35. Hominid to Homo

  36. Genus Homo • Increased brain size • Reduction in size of face and teeth • Increased reliance on cultural adaptations

  37. Evolution of brain size

  38. Brain size in fossil hominids

  39. Proposed species of Homo

  40. Homo erectus • “upright walking human” • Appeared in Africa 1.7-1.8 mya • Possibly as young as 50kya = co-existence w/ moderns • First hominid to migrate out of Africa into temperate parts of Eurasia 1.8 Ma – 500 kya • Primitive cranial traits include large brow ridges, postorbital constriction, flat cranial vault • Derived traits include less prognathism, higher skull vault, smaller teeth, larger brain, modern limb proportions

  41. H. erectus/ergaster sites

  42. KNM-WT 15000 • Most complete H erectus skeleton • “Turkana boy” • ~ 12 years of age • Evidence of modern limb proportions • Tall • Large brain • Appears to be juvenile, not adolescent

  43. Origins of stone tools • Earliest evidence for intentionally modified stone tools is 2.5 mya in East Africa • Earliest stone tools in South Africa ~ 2 mya • Bone tools appear 2-1 mya at Olduvai Gorge (Tanzania) and in South Africa • Oldowan tool technology • H habilis and H rudolfensis • Acheulean tool technology • H erectus

  44. Oldowan tool industry • Mode 1 technology • Simple tools made from rounded stones, flaked to produce sharp edge • Variable form

  45. Importance of Oldowan hominids • Plausible candidates for link between early apelike hominids and later hominids • Studying Oldowan archaeological sites yields insight in processes shaping human evolution • Combining archaeology, ethnography, and biological anthropology informs understanding of transition to modern humans

  46. Oldowan hominids relied on hunting and extractive foraging • Kathy Schick and Nicholas Toth (Indiana) • Experimental studies of Oldowan tool use • Flakes, not cores, may be most important tools • Useful for many functions, including butchering

  47. Bone tools used to dig up bulbs, tubers, excavate termite mounds Swartkrans

  48. Archaeological evidence for meat eating • Oldowan sites at Olduvai Gorge littered with fossilized animal bone from many species • Taphonomic studies suggest most fossils not accumulated by natural processes • Taphonomic studies also show evidence that Oldowan hominids processed carcasses

  49. Taphonomy shows hominids used Oldowan tools to process carcasses Cut marks made by carnivore teeth Cut marks made by stone tools Electron micrographs of 1.8 mya fossil bones from Olduvai Gorge

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