Natural
selection is defined as differential
survival and
reproduction. (1) Differential viability from zygote
to reproductive maturity is the classic mode of natural selection. (2)
Darwin also recognized sexual
selection, in which males and females compete for access to each
other as mates. This may involve selection for traits that compromise
survival, but are effective to mate choice. (3) & (4) Fecundity and gametic selection
affect gamete production and differential representation of alleles in
gametes. For example, T
alleles causing taillessness in various mammal species are
preferentially represented in the gametes of Tt heterozygotes. (5) Gametes
themselves, especially sperm, may have differential ability to survive
in the female reproductive tract and to fertilize eggs, according to
genetic compatability factors.
