Elemental Forces of Organic Evolution
Natural selection on variation action caused evolution and reproductive isolation also has a play a important role.
Sources for Organic Variation
Variation arises in an individual member of a population, and is the differences that occur in the characteristics between members of the same species. Variations are the raw materials for organic evolution. Variation may arise by
Natural Selection Examples:
Example 1: DDT resistant mosquitoes: about 50 years back mosquitoes are killed by DDT but after that DDT resistant mosquito appeared gene mutation had conferred on the mosquito, the ability to resist the effect of DDT.
Example 2: Metal tolerance in grasses: many metal residues collect in the soil near some industries using heavy metals and those are poisonous so kill the grasses. Resistant grasses are found to evolve after some time through the action of variation and natural selection.
Example 3: Industrial melanism: The peppered moth is Biston betularia has dominated the literature on industrial melanism. The moth has light coloured wings dotted with spots blended well with the lichens growing on the houses and trees on which it rested. When mutated form of the moth which was black in colour, it was eaten up by birds, after the industrial revolution, the genes for black wings proved favourable on the soot covered lichens growing on the walls of houses.