"It takes a village to raise a child" is folk wisdom which means that quality communities turn out quality individuals.

It may have seemed like a new idea when First Lady Hillary Clinton said it in the 1990s but ancient societies formed cooperative groups to help raise their children. Why did that happen?

University of Utah anthropologist Karen Kramer and colleagues created an economic model where mothers had one dependent offspring at a time, ended support of their young at weaning and received no help from others and then mapped it to where mothers often have multiple kids who help rear other children.

Most hypotheses about who helped mothers in ancient societies point to other adults but this simulation found that it is a mother's own children who were the most reliable as helpers.  Kramer's method plugged different variables into equations in order to simulate the evolution of families from the past to the present.

Other findings include:

• Human motherhood might have undergone a remarkable transition from a past when mothers likely nursed children until the age of 5 to 6, did not nutritionally support children after weaning, and received no help raising the children. Going back in time, it might be possible to find groups of mothers and cooperating siblings who helped to raise other children. As time progressed, mothers have relied on other adult relatives and fathers to help out. 

• Mothers make tradeoffs. Do they take care of the children they already have, do they have another one, or do they do something else with their time? These same decisions that mothers made in the past are still being made today.

"We simulated an economic problem that would have arisen over the course of human evolution -- as mothers became more successful at producing children, they also had more dependents than they could care for on their own," said Kramer. "We found that early in that transition, it was a mother's older children who helped to raise her younger children and only with more modern life histories did mothers also need the cooperation of other adults. This suggests that early human families may have formed around cooperating groups of mothers and children.

"Humans are extraordinary cooperators. However, most research has focused on adults and we know very little about how cooperation develops in children. We know that the psychological mechanisms that prepare us for a life of cooperation -- such as a sense of fairness and the ability to show empathy, share food and help each other -- begin to develop in very young children. What we need to explore is what children actually do -- how they cooperate and at what price -- in societies where they still play an important economic role."

Citation: "When Mothers Need Others: Life History Transitions Associated with the Evolution of Cooperative Breeding," Journal of Human Evolution