Debates are everywhere: Are sex and gender innate? Is sex natural and gender social?  Is gender the result of sex? But, scientifically, both sex and gender are mosaics, so why are we so obsessed? asks Daphna Joel

Are sex and gender natural? To my mind, a much more interesting question is: why do we care? But first, let me say a few words about the original question.

Sex is a biological system comprised of genes and hormones, and in this sense, it is ‘natural’. By saying that sex is ‘natural’ people tend to imply that it's immutable, yet natural phenomena, including those related to sex, are often subject to change. For example, the levels of sex-related hormones constantly fluctuate, in response to internal and external events. Some of the factors affecting the levels of these hormones are highly dependent on a person's gender. For example, competing and parenting – which in many cultures are not equally encouraged in women and men – affect testosterone levels. Do these facts mean that a person's sex is not natural? Not at all. But they do mean that we should not equate ‘natural’ with ‘immutable.’

Nor should we equate the sex system with the sex categories, to which we are assigned at birth, typically on the basis of the form of our genitals. The vast majority of humans are born with one of two sets of genital organs – either only female-typical or only male-typical. In contrast, such components of the sex system as estrogen, testosterone and other sex-related hormones are found in all humans, regardless of which set of genital organs they possess. Moreover, the average levels of most of these hormones are similar in females and males, and, as I have just discussed, the levels of these hormones are highly dynamic and reactive. So, unlike genitals, sex-related hormones do not come in two distinct sets – male and female.

Complex interactions result in brains composed of unique mosaics of features, and these brain mosaics cannot be meaningfully sorted into male and female.