Question

Geographical and reproductive isolation of organism gradually lead to speciation.

Answer 1

Geographical isolation leads to genetic diversion and reproductive isolation.

These lead to the formation of various species as animals, plants and other organisms as they are separated from exchange genetic material with an organism of same species.

There the theory of cross-species reproduction comes into place which leads to speciation.

Answer 2

Different geographic regions are likely to have different selective pressures. Temperature, rainfall, predators and competitors are likely to differ between two areas 100's or 1,000's of kilometers apart. Thus, over time, the two populations will differentiate. Even if the environments are not very different, the populations may differentiate because different mutations and genetic combinations occur by chance in each. Thus, selection will have different raw material to act upon in each population. Thus geographical and reproductive isolation of organism gradually lead to speciation.