Hominin evolution: WACE Year 12 Human Biology Unit 4
“Describe the major trends in hominin evolution, including bipedalism, brain size and tool use, with reference to key genera”
Hominin evolution shows clear trends: a shift to bipedal (upright, two-legged) walking with matching skeletal changes, an increase in brain size, a reduction in jaw and tooth size and brow ridges, and the development of tool use and culture, traced through genera such as Australopithecus and Homo.
What this dot point is asking
WACE wants you to describe the major trends in the evolution of modern humans and the skeletal evidence for them. Hominins are the group that includes modern humans and our extinct bipedal ancestors and relatives. You are not expected to memorise every species, but you should know the main trends and a few key examples.
Bipedalism: the defining hominin feature
Bipedalism, habitual walking upright on two legs, is the earliest and defining hominin trait, appearing before large brains. It is supported by a suite of skeletal adaptations you should be able to describe and explain:
- Foramen magnum (the hole where the spinal cord meets the skull) is positioned underneath the skull, so the head balances on top of an upright spine.
- Spine is S-shaped (curved) to centre the body's weight over the hips and absorb shock.
- Pelvis is short, broad and bowl-shaped to support the organs and anchor walking muscles.
- Femur angles inward (the carrying angle) so the knees and feet are under the body's centre of mass.
- Foot has an arch and a large, non-opposable big toe aligned with the others, for pushing off while walking.
Bipedalism freed the hands for carrying and using tools and may have helped with seeing over grass and reducing heat exposure.
The fossil evidence shows hominins walked upright long before brain size increased greatly. Early hominins such as Australopithecus were bipedal but had ape-sized brains. Do not claim large brains drove the move to two legs; bipedalism came first.
Trends in the skull, brain and teeth
As hominins evolved, several skull and dental trends appear together:
- Brain size (cranial capacity) increased, from around 400 to 500 cubic centimetres in Australopithecus to about 1350 cubic centimetres in modern Homo sapiens. The forehead became higher and more vertical.
- Brow ridges and the overall robustness of the skull reduced.
- Jaw and teeth became smaller, the face flatter (less prognathous), and a chin developed in modern humans.
- The dental arcade changed from a rectangular ape-like shape to a rounded parabolic arch.
These trends are linked to diet, cooking and the increasing importance of tools and culture over powerful jaws.
Tool use and culture
Cultural evolution runs alongside the physical trends. Stone tools become more sophisticated through the record, from simple flaked pebble tools to finely worked blades, along with the controlled use of fire, art and eventually complex language and society. Culture allowed hominins to adapt to new environments far faster than biological change alone.
Key hominin genera (the examples to know)
You should recognise the broad sequence and the main genera, not exhaustive species lists.
- Australopithecus (for example the "Lucy" specimen, Australopithecus afarensis): bipedal, with a small ape-sized brain, lived in Africa several million years ago.
- Homo habilis ("handy man"): a slightly larger brain and associated with the earliest stone tools.
- Homo erectus: a larger brain again, taller body proportions like modern humans, use of fire and more advanced tools, and the first hominin to spread out of Africa.
- Homo neanderthalensis (Neanderthals): large-brained, robust, cold-adapted, made tools and buried their dead; a close relative rather than a direct ancestor.
- Homo sapiens: modern humans, with the largest and most rounded braincase, smallest face and teeth, a chin, and complex culture and language.
Comparing two crania
Given two skulls, look for the trends. The more recent, more human-like skull will have a larger cranial capacity, a higher and more vertical forehead, smaller or absent brow ridges, a flatter (less projecting) face, smaller teeth and jaw, and often a chin. A skull with a small braincase, heavy brow ridges, a projecting jaw and large teeth is more ape-like and therefore earlier in the sequence. A marker wants you to name specific features and link each to the trend (for example "larger cranial capacity indicates a more recent hominin because brain size increased over time").
How this maps to the exam
Expect questions asking you to list and explain bipedal adaptations, describe trends in brain size, dentition and the skull, or compare two skulls or skeletons and identify which is more recent. You may be asked how a feature such as the position of the foramen magnum indicates bipedalism, so link each structure to its function.
A common error is treating hominin evolution as a single straight line, with each species turning neatly into the next. The hominin family is a branching tree, and several species often coexisted (for example Neanderthals and Homo sapiens overlapped). Also avoid saying humans evolved from chimpanzees; humans and chimpanzees share a common ancestor, they did not descend one from the other.
Exam-style questions
Questions in the style of SCSA exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
WACE 2022-style6 marksDescribe three skeletal adaptations for bipedalism seen in hominins, and explain how each feature supports an upright, two-legged stance and gait.Show worked answer →
A 6 mark response needs three correct features, each linked to its function in bipedalism.
- Position of the foramen magnum
- It is positioned more centrally underneath the skull (rather than at the rear), so the head balances on top of an upright vertebral column.
- Shape of the pelvis
- The pelvis is shorter and broader (bowl-shaped), which supports the abdominal organs above it and provides attachment for muscles that balance the trunk over the legs while walking upright.
- S-shaped spine and angled femur
- The curved spine acts as a shock absorber and positions the centre of mass over the feet, while the femur angles inward (a carrying angle) so the feet sit under the body's midline for balanced striding.
Other valid features include arched feet and a non-opposable big toe.
Markers reward three distinct features each correctly linked to upright posture or efficient two-legged walking.
WACE 2023-style4 marksDescribe two major trends, other than bipedalism, seen across hominin evolution, and identify one key genus that illustrates these trends.Show worked answer →
A 4 mark answer needs two trends plus a relevant genus.
- Increasing brain size
- Cranial capacity increased over time, from the relatively small brain of Australopithecus to the much larger brain of Homo, associated with greater cognition and complex behaviour.
- Changes in dentition and tool use
- Teeth and jaws became smaller and less robust as diet and food processing changed, while tool use became more sophisticated.
- Key genus
- Homo (for example Homo erectus or Homo sapiens) shows the larger brain, reduced dentition and advanced tool use compared with earlier Australopithecus.
Markers reward two clear trends and a correctly matched genus.