Gender shapes our lives in fundamental ways. It impacts everything from the activities we are encouraged to enjoy and the behaviours we are encouraged to display, to the subjects we study, the jobs we do, and the responsibilities we undertake as adults.

Precisely because it structures so much of who we are within society, gender has long been a hotly-debated issue. For decades, feminist thinkers have sought to redress the gender bias of patriarchy, whereby men continue to hold more power, wealth, and influence than women.

In recent years, the gender debate has evolved further, as high-profile awareness campaigns and landmark laws have recognized those who identify outside of the simple division of male and female — those whose gender experience is instead transgender, “genderfluid”, or “genderflux”.

But these steps towards a more gender fluid world have met fierce resistance from those who wish to uphold a clear demarcation between man and woman, and with it, essential – biological – attributes to each gender. Violence against transgender people – in particular black transgender women (women who were assigned male sex at birth) – is on the rise.

The average life expectancy of a trans woman in the Americas is between 30 and 35 years of age. In countries where political and religious conservatism hold sway, the notion of gender fluidity is frequently construed as a dangerous and destabilizing threat to society – in particular to young children.

What’s behind this heated and increasingly vicious debate? Our book Is Gender Fluid? takes a step back from the moral panic and agitated rhetoric to present the key facts on gender fluidity. Here are some of its learnings:

Trinity Mirror/Mirrorpix/Alamy British musician David Bowie is seen here in 1971 with his wife Angie and three-week-old son Zowie. He is wearing an Oxford Bags dress, Turkish cotton shirt and a felt hat. The widely published photographs, by Ron Burton, show both parents challenging gender boundaries.

Gender fluidity is not a new idea
In the Eighteenth Dynasty of Egypt, the female Pharaoh Hatshepsut was depicted in male clothing wearing the traditional Pharaoh’s beard. Ancient Greek mythology also includes numerous references to androgyny, cross-gender, and intersex. Portrayals of the god Aphroditus show him/her with both breasts and a penis.

There is no simple law of nature
Many studies on the animal kingdom seek to uphold a stark binary of the sexes, and to show that the male is naturally inclined to be the protector-provider while the female is naturally inclined to nurture and make the home. In fact, there are important examples of animals that fall outside of this model. Once she lays her egg, the female penguin leaves the nest to spend the winter in the ocean. The male Emperor penguin hatches the egg and nurtures the young chick. The male marmoset (a type of monkey) also cares for the newborn from birth.

Image: Chronicle/Alamy Stock Photo This group of hijra people is from South Asia, where hijra is a term used of trans and intersex people. Although traditionally well-respected members of society, many of today’s hijra suffer from discrimination and poverty.

Many cultures around the world recognize the existence of more than two genders
In Hawaiian and Tahitian cultures, Mahu – literally meaning ‘in the middle’ — is a long-respected third-gender identity, acknowledging both masculine and feminine aspects. In many parts of Latin America, Travesti – a person who was assigned male at birth but identifies as female – also have a long history. In Indonesia, which has the world’s largest Muslim population, the waria people, were likewise assigned male at birth, but live openly as women.

Image: Del Monte. ‘In a Parallel Universe’ by Eli Rezkallah is a collection of fictional images that have been recreated from actual advertisements from the 1950s and 1960s. The series uses role play to humorously challenge contemporary sexism.

Gender is always in flux with changing economic, political and religious systems
Prior to communist rule in China, a woman’s role was seen as primarily domestic and decorative. By contrast, the Communist Party of China launched the maxim ‘Women hold up half the sky’. Far-reaching campaigns advocated for women’s active participation in the workforce, including hard industrial labour.

In early 20thcentury Iran, women were educated and fully immersed in working life – many in public office and politics. But after the Iranian Revolution of 1979, the new Islamic Republic made sweeping changes to gender roles. Women were no longer able to take up jobs in public office, sex segregation was enforced in public spaces, and women were forced to follow the Islamic dress code.

Image: Prints and Photographs Division, Library of Congress, Washington, D.C. Beulah Faith was_an ex-sales clerk from a department store. Here, she is depicted reaming tools on_a lathe machine for Consolidated Aircraft Corp., Fort Worth, Texas, in 1942.

Up to 2% of the population are intersex (DSD)
Intersex describes various conditions in which a person is born with reproductive or sexual anatomy that does not fit into typical definitions of male or female. In medical language, the term DSD (disorders / differences / diversities of sexual development) is also used to describe such conditions. The most thorough existing research estimates that 1.7% to 2% of the population are born intersex. This is about the same, or more, than the percentage born with red hair (1% to 2%).

Find more in Is Gender Fluid? — now available as part of The Big Idea collection, our new series of super-digestible primers on some of the most urgent debates and intricate dilemmas of our times.

Packed full of though-provoking images and with a novel use of fonts to help you skim the book if you only have a half-hour to spare, The Big Idea series brings you all the tools you need to make your own informed decisions and contributions.

Other titles in the series include Will AI Replace Us? and Is Capitalism Working? , and (forthcoming) Is Masculinity Toxic? and Should We All Be Vegan?