noun
: a natural process tending to cause the survival of those individuals or groups best adjusted to the conditions under which they live, resulting from the interaction of the organism in its entirety with all the factors of the environmental complex although any one factor may appear to be decisive for survival or extinction in particular circumstances, and recognized today as a mechanism equally important for the perpetuation of desirable genetic qualities and for the elimination of undesirable as these are brought forward by recombination or mutation of genes — compare darwinism , macroevolution , mendel's laws, microevolution