text: They will if they are near each other when the female is in heat or looking for a mate.  This is one reason why most animals have an in-built tendency to leave the family group when they mature.\n\nIn some animals, the young disperse as far as possible, thus avoiding their siblings.  In many herd species, the males are forced out of the herd when they reach maturity, sometimes forming their own small herds until they can find a new herd full of new blood that they can join.\n\nWhen dispersal routes are blocked by human development, or when populations get low enough that there is little choice in mate selection, incestuous breeding does indeed occur.  In many parts of Africa, the cheetahs are now so inbred that a skin graft taken from one cheetah can be put on another cheetah with virtually no chance of rejection.  There is so little genetic variance that they are nearly clones of each other.