isn’t evidence of an aquatic ape ancestry, as it turns out to be a very general characteristic of air-breathing vertebrates. This reduction in heart rate is just one of the physiological responses that are sometimes described together as the “mammalian diving reflex”. But physiological responses that could be useful in diving are also – and, perhaps, even more importantly – useful for not drowning. While our ability to breath-hold may not be all that special, when we compare ourselves with other animals, it’s now proving very useful in one particular area of medicine. Radiotherapy for breast cancer involves directing radiation, very precisely, at the tumour. This may require several minutes’ worth of radiation and, so, it’s usually done in short bursts, between breaths. But, if the patient can keep her chest perfectly still for several minutes, it means that the entire dose can be delivered, in the right place, in one go. The problem, of course, is that most people, just like me, struggle to hold their breath for much longer than a minute. But doctors at University Hospital Birmingham have recently performed careful experiments that show that, if patients are ventilated with oxygen-rich air before attempting a breath- hold, they can manage to hold their breath for an impressive five-and-a-half minutes. Surprisingly, the trick seems to lie not in fooling the