Prior to the Demographic Transition, fertility in northwestern Europe was controlled by limiting marriage. Marriage was regulated by landowners and the churches, and was not allowed unless a man had accumulated the resources necessary to support a family. Long periods of being landless, a servant, or an apprentice, precluded marriage. Once married, there was no control of fertility. But, only about half of adults were married at any given time, so fertility was about half of what it might have been. Eventually, contraception was accepted and fertility within marriage fell.

European populations grew only slowly during the period 1200-1700; factors include disease and wars. Human feces and rotting animal remains were not sequestered and often contaminated drinking water. Cities were so filthy that more people died in them than were born. About a third of children died in infancy, many from abandonment and lack of care during wet-nursing. Children that survived were subjected to harsh discipline to control their tendency to sin. Ineffective and even harmful treatments, like blood-letting, were all that medicine could offer.

In addition to cultural controls acting to maximize fertility, there are important, and often competing, interests of individual families to limit fertility. Unwanted births are dealt with by infanticide in many cultures. Additionally, fertility is regularly controlled by limiting marriage within a culture. Another very important factor in population growth, especially in the tropics, is food availability. Heavy rains in the tropics wash nutrients away, leaving deficient soils. Much of Africa is either too dry or too wet. Africa was, until recently, not densely populated.

Throughout prehistoric, written, and recent history, human warfare has been commonplace. Nearly all societies engage in regular or periodic war. In many examples, human warfare has characteristics similar to chimpanzee war: an in-group fights with and kills members of the out-group. This information is not to be misinterpreted as either justifying human violence or considering it inevitable. When it comes to births and fecundity, though, humans are very different from the other great apes. Chimpanzees reproduce once every five to eight years; humans can give birth again within 18 months.

Reproduction is not simple or easy, nor is it fair. Females often bear a larger reproductive burden of child bearing and child rearing. Reproductive strategies can be simplified into two primary strategies for males and two for females: males often either engage in sperm competition or physical competition while females strategize to get resources from males, or to find the best male genes for the offspring. Rape and violence, as reproductive strategies, occur in few species, but violence is especially prevalent among the great apes, probably because eggs are so scarce in these species.