06 1.6 Causes of the diversity of life forms through time
Scientists give several explanations for the great variety of living things and the appearance of new species through geologic time.
- Adaptation to different environments (the deep sea, forests, deserts), producing species adapted to each environment.
- Evolution by natural selection, gradually over long periods, or relatively quickly in some cases.
- Accumulated genetic mutations within a group of organisms.
- Geographical isolation: a group of organisms is separated from the rest of its species by a natural barrier such as a mountain range, a wide river or a deep valley. Over time, this can lead to new species. The steps are:
- (i) the barrier interrupts gene flow: the two groups no longer mate, so genes are no longer exchanged;
- (ii) each group accumulates different mutations independently;
- (iii) natural selection in each different environment preserves the favourable traits in each group;
- (iv) differences grow until mating between the groups becomes impossible, and a new species has appeared.
- Change and stability. Earth and living things have changed a great deal, but some rock formations stayed relatively stable.
- The rock layers record these ancient events.
Check.
- Geographical isolation is a cause of the appearance of new species (not of mass extinction).
- The fossil record supports (does not deny) the evolutionary link between the Asian elephant and the mammoth.