Primatologist Sarah Blaffer Hrdy (author of The Woman That Never Evolved, Mother Nature, as well as her latest book Mothers and Others) is one of the leading experts on polygynous mating systems in primates. As she explained to me in our recent correspondence there are several important considerations that have been left out of this story. The most important is the kind of sample bias I referred to earlier if we were to make conclusions about Agatha Christie's work based only on her final novel. The DNA evidence may be a record of the human past, but how far into the past does it actually go? As Hrdy explained:
Keep in mind that in terms of interpreting such genetic evidence we are of necessity confined to a fairly recent time depth (and remember, by “recent” someone like me means the last 10,000 years or so). For this time period multiple lines of evidence do indeed suggest that humans were moderately to extremely polygynous and that women were moving between groups more than men were.
However, humans have been around for far longer than 10,000 years, with conservative estimates placing the emergence of modern Homo sapiens at about 200,000 years ago. A genetic record extending back 10,000 years is remarkable, but it's essentially adding only three more novels to our existing timeline. There is also something very important to consider that dramatically influenced human behavior within the last 10,000 years: the invention of agriculture. Prior to about 12,000 years ago all humans were hunter-gatherers and lived a migratory existence. With the advent of farming some human societies began to remain sedentary for the first time in our history. This change had serious impacts on human life and behavior. Just as Alzheimer's dramatically altered the content of Agatha Christie's work, so agriculture radically transformed human society and, by consequence, sexual behavior.
Hrdy argues that there was a major disruption in human residence patterns as a result of this “agricultural revolution.” In small bands of modern day hunter-gatherers there is a mixture of what anthropologists call matrilocal and patrilocal residence, the practice of women or men to stay within the community they're born into while the other migrates between communities. However, recent research has shown that hunter-gatherer societies today emphasize matrilocal (or bilocal) residence while fewer than 25% are considered patrilocal. This is in stark contrast to the larger scale agricultural societies where an estimated 70% are patrilocal
Via Razib Khan, who has some interesting comments on the issue.