Isolation: Separation of a single population into several sub-units is called Isolation.

Interbreeding does not occur between isolated groups. Each group may develop a set of new traits that lead to evolutionary changes and towards formation of new species.

The isolating mechanisms are of two types:

i. Geographical isolation:

a. It occurs when an original population is separated into two or more groups by geographical barriers such as river, mountain, ocean, island formation, forests, etc.

b. The separated groups are exposed to different kinds of environmental factors. Hence, each group acquires variations by developing mutations, recombination, etc.

c. These variations are processed by natural selection. This leads to progressive genetic divergence. The separated populations develop distinct gene pool and they do not interbreed. Thus, the species are formed by geographical isolation.

d. The classic example of geographical isolation is that of Darwin’s finches.

e. Example: Darwin’s finches living on Galapagos islands differ not only among themselves but also from mainland finches in size, colour, beak and food habits.

ii. Reproductive isolation:

a. Reproductive isolation is brought about by the change in genetic material, gene pool and structure of genital organs.

b. It prevents interbreeding between populations whether they are geographically isolated or living close together.