When journalist and science writer Jane McCredie was in primary school there was a white line painted down the middle of the playground, sharply dividing the boys from the girls. In Making Girls and Boys, McCredie sets out to blur that line, offering a fascinating critique of one of our most fundamental social concepts: the idea that male and female are separate, clearly defined categories.

From the international furore that surrounded the question of South African athlete Caster Semenya’s sex, to the multitude of subtle intersex conditions that could affect as many as two per cent of all newborns, Making Girls and Boys presents us with an array of intriguing case studies that confound our simple understanding of what it is to be male and female. Perhaps more importantly, McCredie cuts through the tabloid noise that often surrounds this topic, writing of her subjects with insight, compassion and empathy.

From conception to puberty and beyond, McCredie examines the biological and environmental forces that go toward determining an individual’s sex and gender, revealing the true malleability and fragility of maleness and femaleness. Along the way she takes a fresh look at the illusive relationship between nature and nurture, and brilliantly debunks the work of evolutionary biologists who claim that the hunting and gathering ways of our distant ancestors have left modern men and women with brains that are hardwired differently.

Making Girls and Boys may overturn many of your most fundamental assumptions, but it is also an optimistic book, highlighting the incredible richness of our experience of sex and gender. It’s a welcome tonic in a world where we continue to be peddled so many constraining myths about what it is to be a man or a woman, and the white line that divides the boys and the girls still remains so stark.

Monica Dux is the co-author of **.