The Descent of Man

two absolutely distinct countries inhabited by the same species, the individuals of which can never during long ages have intermigrated and intercrossed, and where, moreover, the variations will probably not have been identically the same, sexual selection might cause the males to differ.

called unconscious selection

In one country the inhabitants value a fleet or light dog or horse, and in another country a heavier and more powerful one; in neither country is there any selection of individual animals with lighter or stronger bodies and limbs; nevertheless after a considerable lapse of time the individuals are found to have been modified in the desired manner almost uniformly, though differently in each country.

Consequently the whole body of males inhabiting the same country would tend from the effects of constant intercrossing

found that many details of structure in man could not be explained through natural selection, I invented sexual selection;