Charles Darwin married his first cousin and had 10 children. 3 died as infants and 3 were infertile. He was the first to raise the question if incest may cause weaknesses in offspring after studying inbred plants in his garden.

Wolf packs are established according to a strict hierarchy, with a dominant alpha male at the top and alpha female not far behind. Usually this male and female are the only animals of the pack to breed. Packs consist of between five and ten animals – usually offspring from several years. All of a pack’s adults help to care for young pups by bringing them food and watching them while others hunt.