Since their ‘discovery’ in the early twentieth century, sex hormones have played a strong role in the explanation of sex differences in human and other animal behaviours. Within the contemporary sciences of biological psychology and behavioural endocrinology, they are attributed powers to produce sex differences in behaviours such as children's play and adult sexuality. In popular scientific literature, hormonal differences are also thought to demonstrate that women are better suited than men to childrearing, and to underlie the sexes' different capacities for other types of work. British psychiatrist Simon Baron-Cohen, author of The Essential Difference (2004), for example, describes the ways in which prenatal hormonal environments create what he calls male or female brains. The male brain, created by in-utero exposure to testosterone, has skills in systematising, which is ‘the drive to analyse, explore and construct a system’ (Baron-Cohen 2004: 3). Female brains, on the other hand, excel at empathising, which refers to ‘the drive to identify another person's emotions and thoughts and to respond to them with an appropriate emotion’ (Baron-Cohen 2004: 2). These hormonally based drives lead ‘naturally’ to particular jobs: