Friday, November 1, 2013

Why monogamy?

Isn't it interesting that most human societies, even when not in contact with each other, evolved to a model with long-term monogamous families? What made it crucial for evolution to avoid polygyny, communal families or repeated monogamy? Certain biological traits must have been necessary (and sufficient?) for this to happen.

Marco Francesconi, Christian Ghiglino and Motty Perry show that once you put this into the framework of a game theory model with overlapping generations, it all makes sense. You just need three features: children of different ages overlapping (i.e., women cannot bear "too many" children simultaneously), paternal investment (father need to help for children to succeed), fatherhood uncertainty (fathers may not be certain which children are theirs). This means that mothers need to secure the help of fathers by assuring that they are helping the right children thanks to monogamy. The first feature is necessary, but it is not clear to me why. I think it is because it gives more assurance to the father about paternity. Monogamy is then not only the most efficient family form in the sense that it maximizes the number of offspring, this is even amplified because it is the only form that creates altruistic ties between children.

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