Humans became easy prey when they moved from the forest to the savanna, which deprived them of the option of climbing trees to flee predators. This shift made it necessary for the men to actively protect the women and their babies. Only as a result of this protection were women able to give birth in shorter intervals, perhaps once every two or three years. This meant that they could produce offspring about twice as frequently as apes. I would be willing to bet that this rapid reproduction is one of the reasons why we dominate the world today, and not the apes.
Frans de WaalWe, who think like animals living in small groups, must structure a global world. We believe in universal human rights and believe racism and war are wrong. On the other hand, it is our nature to be cooperative and loving almost exclusively with the members of the group to which we feel we belong.
Frans de Waal