Evolutionary psychology isn't all about sex. It all extrapolates to reproductive success eventually, but in my opinion some of the most interesting proposed psychological adaptations are far removed from the textbook miscellany of waist-to-hip ratios, facial symmetries, mate retention, and sexual pageantry.

For example, I'm writing this brief post while on a flight to London, and two rows behind me an infant is screaming its little head off. Its cry sounds sickly, brachial and hoarse, and as my fellow passengers squirm uneasily in their seats and turn the pages of their in-flight magazines at a slightly irritated pace, I'm reminded of a certain adaptationist theory about infant crying from my graduate student days.

The theory goes something like this. The acoustic characteristics of distress cries in infants are specially designed to dupe caregivers into responding quickly. Now the baby behind me sounds like he's about to have a stroke at this rate, but he's also exhibiting that hallmark display of the proposed adaptation, which is a rapid, gasping inhalation between bursts of loud crying. Psychologist Nick Thompson from Clark University has postulated this ‘pitch-to-cry' ratio deceives parents into thinking that the baby is suffering some sort of respiratory distress, which in turn triggers a prompt caregiving response. The idea is that natural selection favoured those infants whose cries mimicked choking sounds because by simulating hyperventilation adults were more vigilant to their needs. As a consequence, these babies (which were our ancestors) would have been less likely to find themselves left alone or with strangers for long periods of time, placed in genuine harm's way.

But I don't know what's going on with this baby, poor dear. It's going to be a long flight.