(i) and have survival value in a particular

(i) Gene Mutation:

The contemporary advances in medical science are characterized by genetic engineering. According to this, if the genes are changed, the human body, that is, its whole physiology, would undergo changes.

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Racial composition or characters undergo change by gene mutation. This is a change in the gene structure of the reproductive cell that in­fluences bodily development.

(ii) Natural Selection:

Darwin has explained evolution natural selection. In order to survive in a particular environment, the human body adapts itself to the cir­cumstances. This brings out a change in racial composition.

Precisely, genes that produce variations and have survival value in a particular environment, will rapidly establish themselves. Thus, albinism offers no advantage and is rare, but heavy skin pigmentation is advantageous in the tropics and spreads quickly.

(iii) Genetic Drift:

If a migrant group by chance bears characters unlike those of the larger group from which it separates, then in the course of time, spe­cially, if further splitting occurs, a population different from the ancestral population would emerge. The American Indians have al­most certainly lost some of the traits of their Mongoloid ancestors in this way.

(iv) Population Mixture:

Today, it is common to find racially distinct populations migrate from one place to another. This results in population mixture. It may also be called inter-breeding. Most existing racial groups today are of this kind.