Testosterone Rex is that familiar story that tells us that risk-taking, competitive, promiscuous masculinity evolved in males to increase their reproductive success, and is therefore built into the male brain and fuelled by testosterone. This belief that "boys will be boys" can (subtly or otherwise) encourage, excuse or exculpate behaviour and patterns that impede progress to healthier communities. But Testosterone Rex is based on outdated science, Cordelia Fine argues. As The Guardian put it, this "is a debunking rumble that ought to inspire a roar.