Too extensive or too frequent genetic mutations generally are deleterious for individuals and species. These mutations often cause important phenotypical changes or defects incompatible with the survival of the body and the continuity of the species.

However small genetic mutations that do not cause the appearing of lethal changes are continuously accumulated in the genetic patrimony of the species. These mutations gradually add to each other giving birth to small phenotypical changes in individuals. These small changes are exposed to the selective criticism of the environment (natural selection) and the more favorable for

survival and reproduction are preserved (the remaider are eliminated as their carriers have difficulty in surviving and reproducing). In this manner the combined processes of accumulation of small mutations and of natural selection incorporate new features in the species and they may even lead to speciation (formation of new species) and promotion of biological diversity.

(Obviously only genetic mutations transmitted by cells that originate new individuals, in sexual or asexual reproduction, have evolutionary effect.)   _{Your Comment}