What Science Says About Sex and Gender Amid Marjorie Taylor Greene and Marie Newman Dispute

Congresswoman Marjorie Taylor Greene has used a sign outside her office to claim there are two genders, male and female, citing "science."

However, experts have told Newsweek the sentiments of the sign go against the scientific evidence on sex and gender.

Taylor Greene put up the sign after her office neighbor Marie Newman placed a pink and blue transgender flag outside her workspace. Newman's daughter is transgender.

Taylor Greene's sign reads: "There are TWO genders: MALE & FEMALE 'Trust The Science!'"

She later tweeted from her personal account: "God created ONLY TWO genders."

However, the terms "male" and "female" are not generally used to describe gender, but rather sex, which relates to biological differences. Sex is partly classified by physical attributes, such as the sex chromosomes we carry, our genes that influence our hormones, what reproductive glands we have, and our genitalia.

Terms such as "woman" and "man" instead correspond to a person's identity in society. Other terms used to describe gender identity include transgender, non-binary, and non-conforming.

Moreover, the scientific consensus is that sex is more complicated than the binary male and female categories. For instance, one in 100 people are thought to have conditions that affect their sex development and therefore cannot be easily categorized as male or female. These differences can be linked to factors such as hormones, and genetics.

The chromosomes, which were thought to determine whether a person is male or female, are less reliable than previously thought. Generally, those who are classed as female have two X chromosomes, and those who are male have one X and one Y. But conditions affecting the body's ability to process testosterone, for example, can see individuals with XY chromosomes have characterizes that we would describe as female.

Simona Giordano, professor of bioethics at the University of Manchester Law School, School of Social Sciences, U.K., told Newsweek: "We do not fully understand how sex develops, but it is clear that the Y and X do not mark the development of a person's sex, at least not on their own."

As well as the X and Y chromosomes, others including TDF, DAX-1 as well as 30 genes play a role in sex differentiation.

"Embryology and developmental psychology give us a much more complex and varied picture of both sex and gender development," said Giordano.

Giordano cited recent studies that have shown trans girls—or people born with penises who identify as female—have responses in a part of the brain called the hypothalamus to smells, spatial awareness, as well as the inner ear that are similar to those of natal girls, and different from natal boys.

Therefore, in a hypothetical world individuals could be classified as girls and boys according to these responses rather than their genitalia. In that society, the transgender girls in the study would be classed as "girls."

"Science shows quite clearly that there are several human sexes, and the number would depend on what features one decided to consider as indicative of one sex or another," said Giordano.

Joz Motmans, the president-elect of the European Professional Association for Transgender Health and guest professor in Gender Studies at Belgium's Ghent University, told Newsweek: "We know from scientific research that variations exist both on the level of physiological sex parameters... as well as on the level of gender identity (how people experience their gender)."

Giordano said: "Nature has not made 'two sexes' or 'two genders': humans have made them; empirical observation shows that there are many sexes and genders, and not only two. Neither nature nor empirical observation tell us how to determine whether an individual is a boy, a girl, or something else—that is, there is no single physical trait, or no set of physical traits, that we can look at to determine whether a person is a man or a woman or something else. Only they can tell us."