Human Evolution and Primatology
What it is
Unit II covers the theories of evolution, the primate order humans belong to, the Oligocene–Miocene fossil apes, and the hominin record from about 7 million years ago to modern humans and their spread. UGC-NET tests fossil–site–finder matches and diagnostic traits. Dates are approximate.
Core concepts
Lamarckism to the Synthetic theory. Lamarck (Philosophie Zoologique, 1809): use and disuse, and inheritance of acquired characters. Neo-Lamarckism revived these in the late 19th century; Weismann's germ-plasm theory (germ line separate from body cells) undercut them. Darwin's On the Origin of Species (1859), with Wallace (joint presentation, 1858), rests on variation, overproduction, struggle and natural selection. Neo-Darwinism drops Lamarckian inheritance. The Synthetic theory (1930s–40s; Fisher, Haldane, Wright, Dobzhansky, Mayr, Simpson; named in Julian Huxley's Evolution: The Modern Synthesis, 1942) fused selection with genetics: evolution is change in allele frequencies through mutation, selection, drift and gene flow.
Neutral theory, cladogenesis, punctuated equilibrium, selection. Kimura's neutral theory (1968): most molecular change is selectively neutral and fixed by drift, the basis of the molecular clock. Anagenesis is change within a lineage; cladogenesis is splitting into branches. Eldredge and Gould's punctuated equilibrium (1972) sets long stasis and brief speciation bursts against phyletic gradualism. Selection is stabilizing (favours the mean, as in human birth weight), directional (shifts it) or disruptive (favours both extremes); balancing selection keeps polymorphism, as with sickle-cell heterozygotes under malaria.
Primate radiation and classification. Le Gros Clark's trends: generalized pentadactyl limbs, nails instead of claws, tactile pads, opposable thumb and big toe, reduced snout and smell, stereoscopic colour vision, a large complex brain, single births and long dependency. Traditional suborders are Prosimii (lemurs, lorises, tarsiers) and Anthropoidea (monkeys, apes, humans); cladistically, Strepsirhini versus Haplorhini, with tarsiers among haplorhines.
Primate characteristics. Hair: body hair with tactile vibrissae; humans have sparse fine body hair and many sweat glands. Cranial: a postorbital bar in strepsirhines, full postorbital closure in anthropoids. Dental: catarrhines 2.1.2.3 (32 teeth); most platyrrhines 2.1.3.3 (36); lemurs and lorises have a tooth comb. Brain: about 400 cc in chimpanzees, 500 cc in gorillas, 1350 cc on average in modern humans. Thumb: true opposability in Old World monkeys, apes and humans; the long human thumb adds Napier's precision grip to the power grip.
Locomotion, posture and social behaviour. Vertical clinging and leaping (tarsiers, galagos, indri); quadrupedalism, arboreal or terrestrial (chimpanzees and gorillas knuckle-walk); brachiation (gibbons and siamangs are true brachiators; spider monkeys add a prehensile tail); habitual bipedalism with upright posture (humans). Social systems: solitary (orangutans), monogamous pairs (gibbons), one-male groups (gorillas under a silverback, hamadryas baboons), multi-male groups (baboons, macaques; chimpanzee fission–fusion).
Extant primates and the great apes. Lemuroidea live in Madagascar; Lorisoidea (lorises, pottos, galagos) in Africa and South–Southeast Asia; Tarsioidea on Southeast Asian islands. Ceboidea (New World) have outward-facing nostrils, three premolars and sometimes prehensile tails. Cercopithecoidea (Old World) have ischial callosities and bilophodont molars. Hominoidea are tailless, with Y-5 molars and a mobile shoulder: gibbon (South–Southeast Asia, longest arms), orangutan (Borneo, Sumatra), gorilla and chimpanzee (Africa). Humans have 46 chromosomes, great apes 48. Against apes, humans show a central foramen magnum, S-curved spine, short bowl pelvis, valgus knee, arched foot with in-line big toe, legs longer than arms, a parabolic arch, small canines, no diastema and a chin.
Oligocene–Miocene fossil primates. In the Oligocene Fayum (Egypt), Parapithecus kept three premolars, while Aegyptopithecus (Simons) had the 2.1.2.3 catarrhine formula and predates the monkey–ape split. Dryopithecus, a Miocene European ape (France, 1856), names the Y-5 molar pattern. Ramapithecus (G.E. Lewis, Siwaliks, 1930s), once hailed as a hominid ancestor, is now merged into Sivapithecus, a Siwalik ape on the orangutan line. Gigantopithecus, the largest primate known, includes G. blacki of Pleistocene China (von Koenigswald, from a Hong Kong drugstore, 1935) and a Siwalik form from Bilaspur.
Pre-hominids and early hominids. Sahelanthropus tchadensis (Toumaï, Chad, about 7 million years), Orrorin tugenensis (Tugen Hills, Kenya, about 6 million years; femur suggests bipedalism) and Ardipithecus ramidus (Aramis, Ethiopia, about 4.4 million years; named Australopithecus ramidus in 1994, renamed 1995; "Ardi" has a grasping big toe). A. afarensis (about 3.9–2.9 million years): Lucy (Hadar, Johanson, 1974) and the Laetoli footprints (about 3.6 million years). A. africanus: the Taung child (Dart, 1925) and Mrs Ples (Sterkfontein). A. bahrelghazali ("Abel", Chad) was the first australopith found west of the Rift Valley. Paranthropus boisei (Zinjanthropus, Olduvai, Mary Leakey, 1959) and P. robustus (Kromdraai, Broom, 1938) have sagittal crests, flaring cheekbones and huge molars.
Homo habilis, Homo erectus and Homo floresiensis. H. habilis ("handy man"; Leakey, Tobias and Napier, 1964; Olduvai) had about 500–700 cc and Oldowan tools. H. erectus had about 750–1250 cc, a long low thick vault, supraorbital and occipital tori, a sagittal keel, no chin; Acheulian handaxes, rare east of the Movius line. Its fossils include the Turkana Boy (KNM-WT 15000, Nariokotome, Kenya, about 1.5 million years), Java Man (Dubois, Trinil, 1891, Pithecanthropus erectus), Peking Man (Zhoukoudian, Sinanthropus pekinensis; lost in 1941) and the small-brained Dmanisi skulls (Georgia, about 1.8 million years, earliest fossils outside Africa). H. floresiensis (Liang Bua, Flores, 2004) stood about 1 m, with about 400 cc; island dwarfing may explain it.
Archaic sapiens and the Neandertals. H. heidelbergensis (Mauer jaw, Germany, 1907); Rhodesian Man (Kabwe, Zambia, 1921); Jinniushan, China (usually classed archaic, though the syllabus also lists it with moderns); Narmada Man (Hathnora, Madhya Pradesh; Sonakia, 1982), first called Homo erectus narmadensis, later archaic sapiens. Neandertals (Neander valley, 1856) ranged from Europe through West Asia (Shanidar, Tabun) to Siberia: brain about 1500 cc, occipital bun, midfacial prognathism, large nose, retromolar space, taurodont molars, no chin, stocky cold-adapted build, Mousterian tools, burials. Their position (pre-Neandertal versus pre-sapiens; species or subspecies) was debated; ancient DNA shows a separate lineage that left about 2 per cent in non-African genomes.
Modern Homo sapiens and dispersal. Omo I (Kibish, Ethiopia, 1967) is about 195,000 years old or more; Cro-Magnon (Les Eyzies, France, 1868) was tall, high-vaulted and chinned; Chancelade (Dordogne) and Grimaldi (Italian Riviera) once carried racial labels now rejected; Lake Mungo (Australia) burials date to about 40,000 years. Out of Africa (Stringer and Andrews; mtDNA "Eve", Cann, Stoneking and Wilson, 1987): moderns replaced archaics. Multiregional (Wolpoff, Thorne, Wu): regional continuity linked by gene flow. Partial replacement: African origin with some interbreeding, as Neandertal and Denisovan DNA now indicates.
Worked example
Reading locomotion from the intermembral index. IMI = (humerus + radius)/(femur + tibia) × 100. Below 100, legs dominate (bipeds, leapers); above 100, arms dominate (suspensory apes). Lengths (cm) are illustrative.
| Primate | Humerus + radius | Femur + tibia | IMI | Reading |
|---|---|---|---|---|
| Human | 32 + 24 = 56 | 45 + 37 = 82 | 68.3 | Bipedal |
| Chimpanzee | 29 + 27 = 56 | 29 + 24 = 53 | 105.7 | Knuckle-walker, climber |
| Gibbon | 25 + 26 = 51 | 21 + 18 = 39 | 130.8 | Brachiator |
- Human: 56/82 = 0.683, × 100 = 68.3. Check: 82 × 0.683 = 56.0.
- Chimpanzee: 56/53 = 1.057, × 100 = 105.7. Check: 53 × 1.057 = 56.0.
- Gibbon: 51/39 = 1.308, × 100 = 130.8. Check: 39 × 1.308 = 51.0.
- Order: human < 100 < chimpanzee < gibbon.
Common traps
- Ramapithecus is no longer a hominid ancestor; it is part of Sivapithecus, on the orangutan line.
- "Australopithecus ramidus" is Ardipithecus ramidus under its first name.
- Kimura's neutral theory explains molecular change by drift; punctuated equilibrium is Eldredge and Gould's.
- Anagenesis is change within one lineage; cladogenesis is branching.
- Most New World monkeys have 36 teeth (marmosets and tamarins 32); Old World monkeys, apes and humans have 32.
Speed technique
- Pair fossil, site and finder: Lucy–Hadar–Johanson; Taung–Dart; Zinj–Olduvai–Mary Leakey; Turkana Boy–Nariokotome.
- Sagittal crest, giant molars, dished face mean Paranthropus; gracile features mean Australopithecus.
- Count premolars: three means platyrrhine or Parapithecus; two means catarrhine.
- Replacement means Out of Africa, continuity Multiregional, interbreeding partial replacement.
Check yourself
- Which Fayum primate predates the monkey–ape split and has the 2.1.2.3 formula?
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Aegyptopithecus — Parapithecus kept three premolars. - Who proposed the neutral theory of molecular evolution?
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Motoo Kimura — 1968; most molecular change is fixed by drift. - Where was Narmada Man found?
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Hathnora, Narmada valley, Madhya Pradesh — by Arun Sonakia, 1982. - Which australopith was the first found west of the Rift Valley?
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Australopithecus bahrelghazali — "Abel", from Chad. - Which primates are true brachiators?
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Gibbons and siamangs — the Hylobatidae.
Try it: Human Evolution and Primatology questions
Real questions from the NET Anthropology bank on exactly this skill. Pick an answer to see the full solution — the intuition, the worked steps, the faster methods and the traps.
The neutral theory of molecular evolution, which holds that most molecular change is selectively neutral and fixed by random genetic drift, was proposed by:
Show the answer and worked solution
Answer: option B
Motoo Kimura proposed the neutral theory in 1968: most changes at the molecular level are selectively neutral and are fixed by random genetic drift rather than by natural selection.
Because neutral substitutions accumulate at a roughly steady rate, the theory underpins the molecular clock.
So the neutral theory was proposed by Motoo Kimura, option B.
The 'Lucy' skeleton of Australopithecus afarensis, found by Donald Johanson's team in 1974, comes from:
Show the answer and worked solution
Answer: option D
Lucy, a partial skeleton of Australopithecus afarensis, was found at Hadar in the Afar region of Ethiopia by Donald Johanson's team in 1974.
Laetoli in Tanzania is the site of the afarensis footprints, Olduvai Gorge of Zinjanthropus and Homo habilis, and Taung of Dart's Taung child.
So Lucy comes from Hadar, Ethiopia, option D.
Which primates are true brachiators, swinging arm over arm beneath branches as their main mode of travel?
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Answer: option A
Brachiation is arm-over-arm swinging beneath branches, made possible by very long arms, mobile shoulders and hook-like hands.
Gibbons and siamangs, the lesser apes, are the true brachiators; chimpanzees and gorillas knuckle-walk on the ground, and tarsiers and galagos cling and leap.
So the true brachiators are gibbons and siamangs, option A.
A primate skeleton gives humerus 30 cm, radius 24 cm, femur 24 cm and tibia 21 cm (illustrative values). Its intermembral index and the locomotion it suggests are:
Show the answer and worked solution
Answer: option B
The intermembral index is IMI = × 100.
Here × 100 = × 100 = 120.0, and the check 45 × 1.2 = 54 confirms it.
An index above 100 means the forelimbs are longer than the hindlimbs, the build of an arm-dominant, suspensory climber.
So the index is 120.0, pointing to an arm-dominant suspensory climber, option B.
Which of the following is NOT a feature of the human skeleton in contrast to that of the great apes?
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Answer: option D
Compared with great apes, humans have a centrally placed foramen magnum, an S-curved spine, a short bowl-shaped pelvis, a valgus knee and an arched foot with the big toe in line with the others.
A divergent, opposable big toe is an ape trait used for grasping branches; the human big toe is aligned with the other toes for push-off in walking.
So the feature that does not belong to the human skeleton is a divergent, opposable big toe, option D.
Answer above — every one shows its working.