Answer:
Darwin's theory consisted of two main points;
1) diverse groups of animals evolve from one or a few common ancestors;
2) the mechanism by which this evolution takes place is natural selection. This SparkNote will first take a look at Origin of the Species, and then more closely examine Darwin's theories.
Explanation:
His On the Origin of Species by Means of Natural Selection (1859) is a sustained argument showing that the diversity of organisms and their characteristics can be explained as the result of natural processes.
