David Haig suggests that babies cry at night to prevent siblings

Science News “Babies cry at night to prevent siblings, scientist suggests”

What’s particularly interesting here is not just the parent-offspring conflict proposed but also the conflict between mothers and fathers that is implied in this theory. In fact, it seems that the only piece of evidence that has any potential to support this hypothesis is this gene that appears to be epigenetically modified by the parents to suit their “evolutionary needs”. Otherwise this seems like a classic evolutionary hypothesis resting mostly on logic: the kind that gets people interested, but one that is pretty impossible to deal with scientifically. Not exactly pseudo-science, but we need some sort of separate bin for “untestable hypotheses” that describes the middle ground between pseudo-scientific hypotheses and those that are actually testable by scientific means.

Beyond issues of testability, I really wonder about the logic behind this theory. An assumption that lies behind Haig’s theory is that the interests of both parents and the child are not perfectly aligned. This is reasonable to assume, but we need to think carefully about how and why their interests might not line up. Haig’s theory assumes that mom’s best interest lies in making babies as frequently as possible, whereas both babies and dads are better served by a delay in the conception of an additional baby. But is this true? Can mothers really maximize their reproductive output by making as many babies as possible? What is the ideal interval between births for mothers if they want to have the maximum number of surviving offspring during their maternal lifetime? The Achilles’ Heel of this theory is the timing of night crying/nursing: these behaviors occur fairly early on in the development of the child (crescendoing at about six months old according to this article), which might cause mom to have children at an interval of 2-3 years instead of maybe every year or so. I wonder if anyone has studied the survival of children born at different intervals in subsistence cultures (our best — if not perfect — window into the reproductive challenges faced by our ancestors). In this data would lie the answer to the question: “Is Haig’s theory based on defendable assumptions?”.

Glad to see my old anthropology professor (formerly at Pomona College) Jim McKenna weighing in on this hypothesis! His course got me thinking about reproductive and parenting issues from an evolutionary perspective.

Thanks to Dan Wright for sending this article my way!