1. Human ancestors and how they compare
Sequence: Australopithecus → Homo habilis → Homo erectus → Neanderthal man → Cro-Magnon man → modern man (Homo sapiens sapiens).
| Member | Approx. cranial capacity (cubic cm) | Key features |
|---|---|---|
| Australopithecus | about 500 | Walked on two legs but partly stooped; large canines, heavy brow ridges, no chin, hairy, short |
| Homo habilis | about 700 | "Handy man": first stone tools; brow ridges, no chin |
| Homo erectus | about 1000 | "Upright man": fully erect; used fire; heavy brow ridges, no chin, taller |
| Neanderthal man | about 1450 | Stocky, slightly stooped; heavy brow ridges, receding chin; buried the dead |
| Cro-Magnon man | about 1600 | Tall, fully erect; small brow ridges, prominent chin; cave paintings, fine tools |
| Modern man (Homo sapiens sapiens) | about 1400 | Fully erect; small canines and brow ridges, prominent chin, little body hair; language, farming |
Trends from Australopithecus to modern man
- Posture: from partly stooped to fully erect, with efficient walking on two legs (bipedalism).
- Cranial capacity: increases (about 500 → about 1400 cubic centimetres).
- Canines: become smaller. Brow ridges: become smaller. Chin: appears (Cro-Magnon and modern man).
- Body hair: decreases. Height: increases.
Humans did not evolve from today's apes; humans and apes share common ancestors.
Key terms
- Cranial capacity
Volume of the braincase of the skull.
- Bipedalism
Walking on two legs.
- Brow ridge
Bony ridge above the eye sockets.
2. Lamarck's theory: inheritance of acquired characters
Jean-Baptiste Lamarck (1809) proposed:
- Use and disuse: organs that are used often become larger and stronger; organs not used become smaller and may disappear.
- Inheritance of acquired characters: changes gained during an organism's life are passed on to its young.
Giraffe: ancestors with short necks stretched to reach leaves; their necks lengthened a little; the longer necks were inherited, generation after generation.
Vestigial organs in humans (reduced, no clear use): vermiform appendix, coccyx (tail bones), ear muscles, nictitating membrane (fold in the eye corner), wisdom teeth. Lamarck explained them by disuse.
Criticism: Weismann cut off the tails of mice for many generations; the young were always born with normal tails. Acquired characters are not inherited, because they do not change the genes in the sex cells (other examples: muscles of a body-builder, pierced ears).
Key terms
- Acquired character
A change gained during an organism's life, not present at birth.
- Vestigial organ
A reduced organ with no clear function, useful in ancestors.
3. Darwin's theory of natural selection; the peppered moth
Charles Darwin (On the Origin of Species, 1859):
- Overproduction: organisms produce far more young than can survive.
- Struggle for existence: food and space are limited, so there is competition — within a species (intraspecific), between species (interspecific) and with the environment.
- Variation: no two individuals are alike; many differences are inherited.
- Survival of the fittest (natural selection): individuals with useful variations survive and reproduce more.
- Inheritance: useful variations are passed on; over many generations they build up and new species arise.
Giraffe (Darwin): necks varied at birth; long-necked giraffes reached more food, survived and bred.
Peppered moth (Biston betularia), England: a light and a dark form.
- Before industry, tree bark was pale with lichens: light moths were camouflaged, dark ones eaten by birds; the light form was common.
- In the industrial 1800s, soot killed lichens and blackened bark: dark moths were camouflaged and light ones eaten; the dark form became common (industrial melanism).
- After clean-air laws in the 1900s, bark grew paler and the light form increased again. The moths did not change colour; birds selected among forms that already existed.
Key terms
- Natural selection
Survival and reproduction of individuals with useful variations.
- Industrial melanism
Increase of dark forms in areas darkened by industrial soot.
- Struggle for existence
Competition for limited resources among the many young produced.
Exam tips
Common mistakes
- Saying humans evolved from monkeys or modern apes.
- Giving exact cranial capacities as fixed values (write "about").
- Saying the peppered moths turned dark because of soot (soot changed the bark, not the moths).
- Mixing Lamarck's "acquired characters" with Darwin's "inborn variations".
- Taking "fittest" to mean strongest.
How marks are usually awarded
- 1 mark: a term, an ancestor, an odd one out with its category.
- 2 marks: two differences, or one theory's explanation of an example.
- 3 marks: the points of Darwin's theory, the moth story with camouflage and inheritance, or three trends.