Human Evolution, Grade 12: The Hominid Sequence, Out of Africa and Five Corrections

This is the one Grade 12 topic where South Africa is not a footnote. It is the evidence.

Swartkrans, Sterkfontein, Kromdraai, Taung, Florisbad, Border Cave, Blombos. A learner in Johannesburg is about an hour's drive from the richest early hominid fossil ground on Earth, and the material names those places properly, which is worth saying out loud because it does not always happen.

This page covers all four units of the topic, and it carries five places where the printed account is either wrong or at odds with itself. One of them is not a wording slip. It tells learners the opposite of how human evolution research has worked for the last fifteen years.

Where this fits in the curriculum

Subject Life Sciences
Grade 12
Term 3 and 4. The topic is split across two terms
Topic Topic 11, Human evolution
Units Unit 1 evidence of common ancestors. Unit 2 the Out of Africa hypothesis. Unit 3 the Cradle of Humankind. Unit 4 alternative explanations
Status No formally assessed practical. This is a reading and reasoning topic
Marks Our worksheet is 60

This page sells you nothing

There is no apparatus in human evolution and we are not going to invent any. No kit, no consumable, nothing to pick, nothing to refill. A supplier that offers you a human evolution kit is selling you printed cards.

The one thing worth spending money on is a bus. The Cradle of Humankind is a World Heritage Site within reach of most Gauteng schools, the Maropeng visitor centre sits near Sterkfontein, and some of the caves are open to the public. A day there does more for this topic than anything we could put in a box.

Unit 1: the evidence that we share an ancestor with apes

The curriculum asks for four kinds of evidence, and learners who can name the four kinds score better than learners who can only recite one of them in detail.

Kind of evidence What it rests on
Anatomical Features shared with African apes, and the features that separate us
Fossil Thousands of specimens from East and southern Africa, sorted into eighteen species
Genetic Mitochondrial DNA, and the molecular clock built from it
Cultural Tool making, and later fire, cooperative hunting and symbolic objects

The sequence, in the order the exam wants it

Hominid Roughly when What matters about it
Ardipithecus About 5,8 to 4 million years ago The name means ground ape. Probably walked bipedally but also climbed. A splayed big toe for gripping branches, small brain of 300 to 370 cubic centimetres
Australopithecus afarensis About 3,3 to 2,8 million years ago Males about 1,5 m, females about 1,05 m. Brain 380 to 550 cubic centimetres. Fossilised footprints in Tanzania confirm bipedal walking, probably with bent knees
Australopithecus africanus Overlapping, southern Africa The Taung child and Mrs Ples. The South African australopithecine
Homo habilis About 2,4 to 1,4 million years ago Larger brain, the first stone tools
Homo ergaster About 2 to 0,2 million years ago The first to leave Africa, close to 2 million years ago. More sophisticated tools, cooperative hunting, fire
Homo erectus Same period, outside Africa The convention used here: African specimens are called ergaster, specimens from elsewhere erectus
Homo sapiens About 0,5 million years ago to now High rounded cranium, small face, a chin, brain about 1 200 cubic centimetres

The point learners miss: bipedalism came before the big brain. Australopithecus walked upright with a brain not much larger than a chimpanzee's. Every question about which came first has the same answer.

Ape-like and human-like features

The exam asks you to sort features into two columns. Most of the list is straightforward.

Ape-like Human-like
Long fingers Head sits vertically on the spine
Crest on the cranium Short, broad pelvis
Prominent brow ridge Angled neck of femur
Prognathous, forward-jutting face Long legs in proportion to arms
Receding chin Big toe not opposable, toes aligned straight
Large canine teeth Large brain, small teeth, foramen magnum underneath the skull

Finding 1: one feature is in the wrong column

You will see "opposable thumb" listed as a human-like feature.

Apes have opposable thumbs. Chimpanzees, gorillas and orangutans all have them, which is why they can grip a branch or pick up a seed. An opposable thumb does not separate a human from an ape, so it cannot do the job that list is asking it to do.

What is actually distinctive Why it works
The big toe is not opposable This is the real discriminator, and it is on the same diagram. An ape's foot grips like a hand. A human foot cannot, because it has been rebuilt for walking
The human thumb is longer relative to the fingers That proportion, not opposability itself, is what allows a precision grip between thumb and fingertip
Position of the foramen magnum Underneath the skull in humans, towards the back in apes, because the head balances on a vertical spine

The same material proves the point against itself. The oldest hominid described in the topic is given a splayed big toe for gripping branches. That is the feature doing the work, and it is a foot, not a hand.

If a question asks for a human-like feature of the hand, say the thumb is long relative to the fingers, not that it is opposable. The second answer is true of a chimpanzee as well.

Mitochondrial DNA, and why it is used

Step Why it matters
An egg carries the mother's mitochondria. At fertilisation the sperm mitochondria are not passed on Mitochondrial DNA descends down one line only, so it is never shuffled by meiosis
Each time mitochondrial DNA is copied there is a chance of a mutation Mutations build up at a steady rate, which turns the molecule into a clock
Mutations spread inside an isolated population but not between populations Two populations that split keep drifting apart, and the gap records the split
Few differences means a recent split, many differences means an old one This is how the branch points on a cladogram are dated

The cladogram built from this gives roughly 15 million years for the common ancestor of all the apes and humans, and about 5 million years for the common ancestor of humans and chimpanzees.

Finding 2: the claim that fossils contain no DNA

You will read that "fossils do not contain DNA, so we cannot include fossils on a cladogram."

That is not a wording slip. It is false, and it is the most important error on this topic.

DNA has been recovered from hominid fossils and used to place them on exactly the kind of tree the sentence says is impossible. The Neanderthal genome was sequenced from fossil bone. An entire population, the Denisovans, was identified from the DNA in a single finger bone before anybody had a skull to go with it. The work of extracting DNA from ancient bone won the 2022 Nobel Prize in Physiology or Medicine.

The fair version
DNA does not survive in most fossils. It breaks down with time and heat, so the two and three million year old australopithecine material from a warm African cave yields none, and that part of the tree really is built from bone shape alone
But it does survive in some, particularly younger material and material from cold, dry, stable conditions, and where it survives it is read
So the honest sentence is "DNA rarely survives in fossils", not "fossils do not contain DNA"

Why this one matters more than the others. A learner who believes fossils hold no DNA cannot follow a single news report about human origins, because ancient DNA is where almost all the new findings now come from. The other errors on this page cost a mark. This one costs the subject.

Cultural evidence: tools

Tool making is treated as evidence in its own right, and it moves in steps: the first stone tools with Homo habilis, more sophisticated tools with Homo ergaster alongside fire and cooperative hunting, and later symbolic objects. At Blombos Cave on the southern Cape coast, marine shell beads and bone tools date back about 75 000 years.

Finding 3: one claim worth hedging

You will read, flatly, that Homo ergaster "could talk".

Nobody knows that. Speech leaves no direct fossil evidence. It is inferred from the shape of the skull base, the size of the spinal canal in the neck, and the complexity of the tools they made. Those are reasonable grounds for thinking they had some form of speech, and they are not proof, and a learner should be taught the difference between an inference and a finding in a topic that is built almost entirely on inference.

Unit 2: Out of Africa

The hypothesis: Homo sapiens evolved in Africa and spread from there, replacing earlier populations already living in Africa and Asia.

Roughly when What happened
About 160 000 years ago Movement northwards into North Africa
About 120 000 years ago Movement southwards, as far as southern Africa
About 100 000 years ago A first crossing into the Middle East, following the Nile. This migration died out
About 85 000 years ago A second crossing, into the Arabian Peninsula, which did not
About 60 000 years ago Along the coast into Asia, reaching China

Two reasons are offered for why they left: following migrating herds across a Sahara that was green at the time, and population pressure during warm, wet periods pushing groups outwards to find food and space.

Finding 4: two dates for the same event

The species summary states that Homo sapiens migrated out of Africa "from about 130 000 years ago". The Out of Africa section states that the first humans crossed into the Middle East "about 100 000 years ago".

Those are not the same claim, and nothing in the topic reconciles them.

What to do with it
If a question asks when Homo sapiens left Africa, give the date from the section the question comes from and say which
Better, say that estimates range from about 130 000 to about 100 000 years ago and that the dates move as new sites are dated
That second answer is both correct and more honest, and it is how the science actually works

Dates in this topic are not fixed facts. They are the best current estimate from the fossils found so far, and one new site can move them. Teaching them as constants sets learners up to be confused the first time they read a news report.

Unit 3: the Cradle of Humankind

Fact Detail
Where Near Krugersdorp, Gauteng
Status Declared a World Heritage Site in 1998
Size of the claim More than twelve major hominid fossil sites. Over 35 percent of the world's early hominid fossils have come from it
What has been found Skulls, jaws, teeth, almost complete skeletons, animal fossils, fossilised wood and thousands of stone tools dating from 4,7 to 1,5 million years ago
Why the fossils are there Dolomite caves. Dolomite is a limestone. Underground caves formed in it, and bone was preserved in breccia, a rock of older fragments cemented together
Named sites Sterkfontein, Swartkrans, Kromdraai, Drimolen, Gladysvale, Coopers, Bolt's Farm, Wonder Cave, Plover's Lake, Haasgat, Motsetse, Minnaars
To visit Some caves are open to the public, and there is a museum at the Maropeng visitor centre near Sterkfontein

Finding 5: the same name is used for two different things

Within a few lines, "Cradle of Humankind" is used for the whole continent of Africa and then for the World Heritage Site near Krugersdorp. Those are not the same place and they are not the same size.

In an exam, the Cradle of Humankind means the site near Krugersdorp. If a question asks where it is, Gauteng is the answer, not Africa.

Attached to the wider use is the statement that Africa "is the only continent that has provided evidence of human evolution". The same topic describes Homo erectus specimens from outside Africa and traces migrations through sites in the Middle East and Asia, so the sentence disagrees with its own account two units later. The defensible claim is that Africa is the only continent with evidence of the earliest hominids, which is a strong enough claim without stretching it.

The South Africans who found the fossils

This is examinable, and it is the part learners most enjoy.

Scientist What they did
Raymond Dart Described the Taung skull. The scientific community rejected his claim that it was a human ancestor, and he gave up hominid work. He lived to see himself proved right
Robert Broom Found Mrs Ples, the first adult Australopithecus africanus skull, which vindicated Dart. Also found the Kromdraai specimen now called Paranthropus robustus
John Robinson Worked with Broom at Sterkfontein, Kromdraai and Swartkrans
Phillip Tobias Studied under Dart and succeeded him. Became a world authority and named many hominids, including Homo habilis
CK Brain Changed the picture of early ape-men from violent hunters to hunted animals, by showing the bones in the caves were brought there by predators. Founded taphonomy
Ron Clarke, with Nkwane Molefe and Stephen Motsume Little Foot. Clarke spotted a broken tibia in a store room in 1994 and asked the two assistants to find the other end in the cave wall. They found it in two days. Ten years of excavation produced most of a skeleton
Lee Berger Found Australopithecus sediba at Malapa, and fossils at Coopers and Gladysvale
Andre Keyser Drimolen and Gladysvale. Found the most complete Paranthropus robustus skull ever recovered
Christopher Henshilwood Directs the Blombos Cave project. Shell beads and bone tools from about 75 000 years ago
TF Dreyer Found the Florisbad skull in 1932, dated to 259 000 years
Francis Thackeray Recognised that Mrs Ples was not female but a teenage boy. The nickname stuck anyway
James Kitching Excavated several cave sites including the limeworks at Makapansgat

Two things worth saying to a class about that table.

The Taung skull is described as the world's first hominid fossil. It was not. European fossils had been described decades earlier. What the Taung child actually was is the first Australopithecus ever found and the first early hominid fossil from Africa, which is why it mattered: it moved the search for human origins to the right continent. That is a bigger claim than the one the text makes, and it has the advantage of being true.

Little Foot and Mrs Ples are both good stories about how science actually works. One is a fossil found in a store room by someone who looked properly at a broken bone. The other is a famous specimen whose famous name turned out to describe the wrong sex, and which nobody renamed.

Unit 4: the alternatives section

The curriculum closes the topic by asking learners to be aware that many cultures and religions have their own accounts of the origin of life, and that these are held sincerely by many South Africans.

What the exam asks for here is awareness and respect, not argument. The scientific content examined is the evidence in Units 1 to 3. A learner is not asked to choose, and should not be put in the position of defending a belief in a Life Sciences class.

What you should be able to do by the end

  • Name the four kinds of evidence for a common ancestor, and give an example of each
  • Put the hominids in order and say what changed at each step
  • Say that bipedalism came before brain enlargement, and give Australopithecus as the evidence
  • Sort features into ape-like and human-like, and know which one in the usual list does not belong
  • Explain why mitochondrial DNA is used, and read a cladogram
  • State the Out of Africa hypothesis and give a range of dates rather than a single number
  • Say what the Cradle of Humankind is, where it is and why it matters, with the 35 percent figure
  • Name South African scientists and the fossils they are attached to

Free worksheet and marking memo

Both free, no sign up, straight to the PDF.

  • Learner worksheet, 60 marks, covering the four kinds of evidence, the hominid sequence, ape and human features, mitochondrial DNA, the Out of Africa hypothesis and the Cradle of Humankind
  • Marking memorandum, with the five answers that look right and score nothing

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