The book ranges widely over the scientific investigations of the differences between male and female in humans and other animals. Saini looks at the bias towards male subjects in medical research, and peers into studies of hormonal and gender influences on brain size and structure. She examines the evolutionary and ethnographic evidence for differences in behaviour, work patterns, social power and sexual promiscuity, and digs into the intriguing theories that are competing to attribute the menopause to the influence of patriarchy or of the role of grandmothers in childcare.

Step by step Saini reveals that in all these areas, early findings of clear differences between men and women – almost invariably to the advantage of men – have frequently unravelled upon deeper and broader scrutiny. Disparities evaporate when one takes a more holistic view of the variation between individuals, or extends the investigation to other animal species or human tribes, or simply repeats the experiment with better controls. Saini leavens her careful dissection of the science of gender differences with surprising accounts of the hunting prowess of Agta tribeswomen in the Philippines, the habitual affairs of married Himba mothers in northern Namibia, and the violent dominance of female bonobos over males (the inverse of chimpanzee behaviour).

The tone throughout is measured. Saini's even-handed treatment of disagreements over the proper interpretation of results and observations should give even hardened sceptics pause for thought. Her balanced approach is reinforced by the care taken at every turn to cite her sources. The text might lose a little poetry because of this attention to detail, but it is a price worth paying to make the book as resilient as it needs to be. Although respect for evidence is often spouted as the sine qua non of science, the reality is often very different – especially in the study of human behaviour, which is so readily perturbed by norms and presumptions that affect us all. The prickliness of some of Saini's interviews with male researchers is telling, but not as revealing as the accounts of some of the women scientists she spoke to. Primatologist Sarah Blaffer Hrdy, whose work in the 1970s on Langur monkeys challenged established ideas about female passivity and promiscuity, met stiff resistance from male colleagues that was not altogether scientific: stick to housework, she was told.