Human
Humans have a long period of development after birth. Their life depends less on instinct than other animals, and more on learning. Humans are also born with their brains not so well developed as those of other mammals. This makes for an unusually long childhood, and so makes family life important. If their brains were better developed at birth, their head would be larger, and this would make birth more difficult. In birth, the baby's head has to get through the 'birth canal', the passageway through the mother's pelvis.