equal numbers of black and white rabbits, and hence equal numbers of chromosomes with "B" or "b" allele, still floating around in that population. Every time a white rabbit mates with a black one, only gray rabbits results. So, in order for the results to "click", there needs to be a force causing white rabbits to choose other white rabbits, and black rabbits to choose other black ones. In the case of the finches, this "force" was geographic/niche isolation. This leads one to think that disruptive selection can't happen and is normally because of species being geographically isolated, directional selection or by stabilising selection. See also Character displacement Balancing selection Directional selection Negative selection (natural selection) Stabilizing selection Sympatric speciation Fluctuating selection Selection References Selection