Even for evolutionary psychology, this latest finding is really bizarre. Cell phone bills suggest women avoid talking to their fathers during periods of high fertility, which might be a relic of an evolutionary imperative to avoid mating with close relatives.
Let's take this one piece by piece to see if it gets any less bizarre. First, University of Miami psychologist Debra Lieberman explains that avoidance of close male relatives during fertile periods is a common animal behavior:
"Evolutionary biologists have found that females in other species avoid social interactions with male kin during periods of high fertility. The behavior has long been explained as a means of avoiding inbreeding and the negative consequences associated with it. But until we conducted our study, nobody knew whether a similar pattern occurred in women."
That's the sort of thing that's easy enough to observe in animals, but how can you possibly pick up on that in modern humans? The study hit upon an interesting solution - they used the cell phone records of 48 women of reproductive age. They examined when the women called their fathers and vice versa, then did the same for the women and their mothers. They then compared that data to when women were most and least fertile during the same span.
Their findings suggest there's something going on. The women in the study were half as likely to call their fathers during high fertility days as they were during low fertility days, and they talked to their fathers far less during high fertility, regardless of who actually called. They found women talked to their fathers 1.7 minutes per day during high fertility compared to 3.4 minutes per day during low fertility.
The researchers believe that this evidence of inbuilt psychological mechanisms that drive women away from mates that would produce less healthy children, and the least desirable mate for any woman is her own father. Lieberman explains:
"In humans, women are only fertile for a short window of time within their menstrual cycle. Sexual decisions during this time are critical as they could lead to pregnancy and the long-term commitment of raising a child. For this reason, it makes sense that women would reduce their interactions with male genetic relatives, who are undesirable mates."
Women didn't have the same aversion to talking to their mothers - indeed, it was quite the opposite. Many women talked to their mothers more often during periods of high fertility, and they were four times as likely to call their mothers as their fathers during high fertility. So the aversion does seem to be centered on the father-daughter relationship.
Fellow researcher Martie Haselton says the findings are strong evidence of an evolutionary imperative:
"This suggests that although human culture has in many ways changed at a rapid pace, our every day decisions are often still tied to ancient factors affecting survival and reproduction. We think of ourselves as being emancipated from the biological forces that drive animal behavior. But, that's not completely true. These kinds of findings show us that a complete understanding of human behavior needs to involve these biological forces. Humans are, after all, mammals."
It's an interesting finding, to be sure, but I'll admit I'm skeptical. As much as the raw findings seem fairly persuasive that something is going on here, there are also a lot of assumptions going into that final conclusion, particularly when we're only working from the cell phone records of 48 people. There are a lot of potential confounding factors here, including more psychological or even social and physiological reasons why women - or, perhaps more importantly, the particular women in this study - might not want to talk to their fathers during periods of high fertility, and those reasons might prove to not be true of the entire species.