"In our own species, over-protected children will always suffer in adult social contacts. This is especially important in the case of only children, where the absence of siblings sets them at a serious initial disadvantage. If they do not experience the socializing effects of the rough-and-tumble of the juvenile play groups, they are liable to remain shy and withdrawn for the rest of their lives, find sexual pair-bonding difficult or impossible and, if they do manage to become parents, will make bad ones."