Man has modified some of his animals, without necessarily having attended to special points of structure, by simply preserving and breeding from the fleetest individuals, as with the race-horse and greyhound, or as with the game-cock, by breeding from the victorious birds.
Gizakiak animalia batzuk puntu bereziei begira nahitaez jokatu gabe aldatu ditu, banako bizkorrenak gorde eta umaraziz besterik gabe, xarlangoa eta lasterketa-zaldiaren kasuan adibidez, edo banako garaileak gordez, auzka-oilarraren kasuan.