the major trends in hominin evolution, including bipedalism, brain size, tool use and dentition; Australopithecus and Homo species; and the out-of-Africa hypothesis for the spread of Homo sapiens

What this dot point is asking

VCAA wants the major trends of hominin evolution (bipedalism, brain size, tool use, dentition), the key fossil species from Australopithecus to Homo sapiens, and the out-of-Africa hypothesis for the spread of modern humans.

The answer

Hominins are the group containing modern humans and all their fossil ancestors after the split from the chimpanzee lineage, around 6 to 7 million years ago. Hominin evolution shows clear trends, although the tree is bushy rather than a single line.

Major trends in hominin evolution

Bipedalism. Walking upright on two legs is the earliest hominin innovation, appearing before brain expansion. Anatomical signs:

• Foramen magnum (hole for the spinal cord) moves from the back of the skull (quadrupedal apes) to the centre (bipedal humans).
• Pelvis becomes short and bowl-shaped to support upright posture; the gluteal muscles enlarge.
• Spine develops an S-shaped curve (lordosis and kyphosis) for balance.
• Femur angles inward (valgus angle) so the knees track under the body.
• Foot develops longitudinal arch; the big toe lines up with the other toes (no longer opposable).

Australopithecus afarensis (the famous "Lucy", about 3.2 million years ago) shows nearly all of these features.

Brain size. Cranial capacity rises through the lineage:

• Australopithecus afarensis: about 400 cm3 (similar to a chimpanzee).
• Homo habilis: about 650 cm3.
• Homo erectus: about 900 to 1100 cm3.
• Neanderthals (Homo neanderthalensis): about 1500 cm3 (slightly larger than modern humans).
• Homo sapiens: about 1350 cm3.

The increase is most rapid from Homo erectus onwards. Larger brains correlate with more complex tool use, cooperation, and language.

Tool use and culture. Stone tools become progressively more sophisticated:

• Oldowan (about 2.5 million years ago, Homo habilis): simple pebble choppers and flakes.
• Acheulean (about 1.7 million years ago, Homo erectus): symmetrical hand axes worked on both faces.
• Mousterian (about 200,000 years ago, Neanderthals and early Homo sapiens): prepared-core flake tools.
• Upper Palaeolithic (about 40,000 years ago, Homo sapiens): blade tools, projectile points, art, jewellery.

Control of fire (by Homo erectus around 1 million years ago) and cooking are linked to the dietary changes below.

Dentition. Jaws and teeth become smaller and less robust:

• Australopithecines have large molars with thick enamel, suited to tough plant material.
• Canines shorten and the dental arcade rounds (from a U-shape in apes to a parabolic shape in humans).
• Jaw musculature reduces; the brow ridges shrink; the chin develops.

These changes are consistent with softer, cooked, more varied diets and a shift away from heavy plant chewing.

Key hominin species

Australopithecus afarensis (about 3.9 to 3.0 million years ago, East Africa). Small brain (around 400 cm3), bipedal, ape-like skull and small body. "Lucy" is the most famous specimen.

Australopithecus africanus (about 3 to 2 million years ago, southern Africa). Slightly larger brain (around 450 cm3), more gracile face.

Paranthropus boisei and robustus (about 2 to 1 million years ago). Robust australopithecines with massive jaws and chewing muscles. Evolutionary side-branch; not ancestral to Homo.

Homo habilis ("handy man", about 2.4 to 1.5 million years ago). First Homo species. Brain about 650 cm3. Associated with Oldowan stone tools.

Homo erectus (about 1.9 million to 100,000 years ago). Brain 900 to 1100 cm3. First hominin to leave Africa (around 1.8 million years ago, reaching Asia and possibly Europe). Used Acheulean tools and controlled fire.

Homo neanderthalensis (about 400,000 to 40,000 years ago, Europe and western Asia). Stocky, cold-adapted, large brain (around 1500 cm3). Buried their dead, used Mousterian tools, interbred with Homo sapiens.

Homo sapiens (about 300,000 years ago to present, originated in Africa). Anatomically modern. The only surviving hominin.

Homo floresiensis and Denisovans are recently discovered species that overlapped with early Homo sapiens.

The out-of-Africa hypothesis

The out-of-Africa hypothesis (recent African origin model) is the dominant account of modern human origins. It proposes:

1. Origin. Anatomically modern Homo sapiens evolved in Africa around 300,000 years ago (the oldest known fossils are from Jebel Irhoud, Morocco, dated to 315,000 years ago).
2. Dispersal. Beginning around 70,000 to 60,000 years ago, populations of Homo sapiens migrated out of Africa in waves.
3. Spread. Modern humans reached the Middle East by 100,000 years ago (early excursion), Australia by 65,000 years ago, Europe by 45,000 years ago, and the Americas by around 15,000 to 20,000 years ago.
4. Replacement (with some interbreeding). Earlier hominin species (Homo erectus, Neanderthals, Denisovans) were replaced. Modern non-African humans carry small fractions of Neanderthal DNA (about 1 to 2 per cent) and some Asian and Oceanian populations carry Denisovan DNA (up to 5 per cent in Melanesians), indicating limited interbreeding.

Evidence supporting out-of-Africa.

• Fossils. The oldest anatomically modern human fossils are African.
• Mitochondrial DNA. All living humans share a matrilineal common ancestor in Africa about 200,000 years ago ("Mitochondrial Eve"). African populations have the greatest mtDNA diversity, consistent with longest occupation.
• Y-chromosome DNA. Similar story for the patrilineal line ("Y-chromosomal Adam").
• Archaeology. Dates of first modern human arrival on each continent follow an out-of-Africa wave.

The competing multiregional hypothesis (modern humans evolved in parallel from Homo erectus populations on several continents) is no longer supported by genetic data.

Examples in context

Example 1. Lake Mungo and the spread of Homo sapiens. Lake Mungo in southwestern NSW yielded the famous Mungo Lady and Mungo Man burials, dated to about 42,000 years ago. The skeletons are anatomically modern Homo sapiens. They show Mungo's people walked bipedally with a fully modern pelvis, had brain volumes around 1400 cubic cm (within modern range), used sophisticated stone tools and ochre burial practices. Their presence supports the out-of-Africa hypothesis: Homo sapiens left Africa around 60,000 years ago and reached Australia within 15,000 to 20,000 years, by then displacing or absorbing earlier hominins along the way. The Willandra Lakes World Heritage site is custodial home to the Paakantyi, Mutthi Mutthi and Ngiyampaa people.

Example 2. Australopithecus to Homo dental changes. Comparative palaeontology displayed at Museum Victoria shows Australopithecus afarensis (Lucy, 3.2 Mya) had large molars with thick enamel for chewing tough plant material. Homo habilis (2 Mya) had smaller molars and used stone tools to process food before chewing. Homo erectus (1.8 Mya) showed further dental reduction, expanded brain (around 900 cubic cm), and habitually upright gait. By Homo sapiens, molars are reduced again, the chin is prominent, and the cranium is globular over a brain of around 1350 cubic cm. The trend - reduced dentition, increased brain size, sustained bipedalism, escalating tool use - traces the major hominin evolutionary changes.

Try this

Q1. Identify four major trends in hominin evolution from Australopithecus to Homo sapiens. [4 marks]

• Cue. Brain volume increases; dentition reduces (smaller molars and canines); bipedalism becomes obligatory; tool complexity grows; behavioural sophistication (language, art) emerges late.

Q2. Cranial capacities are: A. afarensis 450 cc, H. habilis 600 cc, H. erectus 900 cc, H. sapiens 1350 cc. (a) Calculate the percentage increase from A. afarensis to H. sapiens. (b) Sketch in words the shape of the cranial-capacity-versus-time graph. [3 marks]

• Cue. (a) (1350 - 450)/450 = 200 percent increase. (b) Roughly linear increase over 3 million years, with steeper rise after 2 Mya.

Q3. Refer to the out-of-Africa hypothesis. (a) Outline the hypothesis. (b) Identify two lines of evidence supporting it. (c) Suggest one finding that would challenge the strict out-of-Africa model. [2+2+2 marks]

• Cue. (a) Modern humans originated in Africa around 200,000 years ago and dispersed globally from 60,000 years ago. (b) African mtDNA shows highest diversity (older population); fossil age gradient from Africa outward; ancient DNA from non-African Homo sapiens matches African ancestry. (c) Evidence of substantial interbreeding with other Homo species (Neanderthal, Denisovan) - this has indeed required modifying the strict model.