Question

Why do human mostly give birth to single baby at a time?

Answer 1

In human beings, female only develop one egg in one cycle, so it is a basic reason for only one child. Other than that human babies are very vulnerable and depends on the mother for years, so to promote the survival rates, one baby is born at a time 

Answer 2

Human mostly give birth to a single baby at a time because the egg of a woman release only one at a time so the sperm combine with the egg and it provide one baby at a time