Parenting behaviors are tied to the genetic link to children, and one obvious question comes from what happens with stepparents or situations in which the identity of the father is less certain. In these cases, problems are more common. In some cultures, mothers who re-marry are expected to place the children from their first marriage with other relatives. The new father wants a household of children only related to him. Even in cultures with less drastic expectations, Pinker argues that stepparents don’t have the same connection to children who aren’t theirs biologically. Even if they grow to love their stepchildren or at least care for them, they are not biologically wired to feel as connected to their stepchildren or to want their stepchildren’s genes to spread the way they want their own genes to spread.

A mother’s first decision when she has a child is whether to keep it. The decision is legitimate as raising a child requires a lot of resources and sacrifice. If the child is sick or may not survive for other reasons, it is not worth sacrificing the mother’s health and considerable resources for the child. Infants are designed to sway the equation in their favor. They look cute and promote the release of oxytocin, both of which increase bonding.