What are the four main points of Darwin's idea of natural selection?

Question

What are the four main points of Darwin's idea of natural selection?

Answer 1

1. Organisms have changed over time, and the ones living today are different from those that lived in the past. Furthermore, many organisms that once lived are now extinct. The world is not constant, but changing. The fossil record provided ample evidence for this view.

2. All organisms are derived from common ancestors by a process of branching. Over time, populations split into different species, which are related because they are descended from a common ancestor. Thus, if one goes far enough back in time, any pair of organisms has a common ancestor. This explained the similarities of organisms that were classified together -- they were similar because of shared traits inherited from their common ancestor. It also explained why similar species tended to occur in the same geographic region.

3. Change is gradual and slow, taking place over a long time. This was supported by the fossil record, and was consistent with the fact that no naturalist had observed the sudden appearance of a new species. [This is now contested by a view of episodes of rapid change and long periods of stasis, known as punctuated equilibrium].

4. The mechanism of evolutionary change was natural selection. This was the most important and revolutionary part of Darwin's theory, and it deserves to be considered in greater detail.