The basic idea of his Origin of Species is that in nature there is a process similar to what goes on in the breeding of domestic plants and animals. If a breeder wants to produce a variety with certain characteristics, he/she keeps an eye out for individuals that have some approximation to those characteristics and breeds from them and not from individuals that do not have something like the desired characteristics. The other individuals may be destroyed, or they may just (...) be segregated; at any rate they are not allowed to breed with the selected stock. The breeder follows this policy also with the second generation of the offspring of the selected individuals of the first generation; those that after all do not have the desired characteristics are rejected, those that do are selected to produce the third generation, and so on. The whole process presupposes some degree of variability within the plant or animal being bred from. There have to be spontaneously produced individuals with something like the desired characteristics for the breeder to select. What can be accomplished by selection breeding depends of the range of variation that occurs spontaneously. (Hence the topic of Darwin's book of 1868, Variation of Plants and Animals under Domestication.) See in the Readings book the picture of the different breeds of pigeons from the Illustrated London News, 1864; Darwin was a pigeon fancier. (shrink)