Sexual Sex"u*al, a. [L. sexualis, fr. sexus sex: cf. F. sexuel.] Of or pertaining to sex, or the sexes; distinguishing sex; peculiar to the distinction and office of male or female; relating to the distinctive genital organs of the sexes; proceeding from, or based upon, sex; as, sexual characteristics; sexual intercourse, connection, or commerce; sexual desire; sexual diseases; sexual generation. Sexual dimorphism (Biol.), the condition of having one of the sexes existing in two forms, or varieties, differing in color, size, etc., as in many species of butterflies which have two kinds of females. Sexual method (Bot.), a method of classification proposed by Linn[ae]us, founded mainly on difference in number and position of the stamens and pistils of plants. Sexual selection (Biol.), the selective preference of one sex for certain characteristics in the other, such as bright colors, musical notes, etc.; also, the selection which results from certain individuals of one sex having more opportunities of pairing with the other sex, on account of greater activity, strength, courage, etc.; applied likewise to that kind of evolution which results from such sexual preferences. --Darwin. In these cases, therefore, natural selection seems to have acted independently of sexual selection. --A. R. Wallace.