03/08/2024 – 15:59
The uproar surrounding Algerian boxer Imane Khelif at the Paris Olympics has reignited the debate over what defines a woman. Spoiler alert: those who argue based on “biology” are almost always wrong. Our gender is identical to our sex; it is written in our genes, can be clearly determined and does not change throughout life. A woman is on the polar opposite of a man – she is either a princess or a knight, and there is absolutely nothing in between. No matter what you say, your sex is the one you were born with. Period. Those who think this way – many, including those involved in the debate over whether Algerian boxer Imane Khelif should be allowed to compete in the Paris Olympics – usually base their argument on one argument: “It’s a question of science” – biology, to be more precise.
But the scientific consensus has changed: sex is a spectrum. If you want to stick with the argument that women and men are on opposite ends of the spectrum, you need to know that there is a lot of variation between the two.
Genetics is clearly ambiguous
XX chromosomes = female; XY chromosomes = male. This is how we learn, in school, that sex is defined.
In people with XX chromosomes, the vagina, uterus and ovaries are usually formed in the uterus itself. In the case of XY, fetuses usually develop a penis and testicles.
There are people whose physical aspects are feminine, but who carry the “male” XY chromosomes in their cells, and vice versa.
A gene located on the shorter arm of the Y chromosome, called SRY, determines (along with other factors) whether testes will form in an embryo. If, for example, this gene is not ready because of a mutation, or if it is dormant, so to speak, the organ will not develop – and this despite the presence of the XY chromosomes.
On the other hand, testicles can develop in people with XX chromosomes if the gene is passed to the X chromosome (possibly during the process of cell division).
So how delicate is it to determine the sex of a child shortly after birth, based solely on visible external sexual characteristics?
Nothing is as immutable as it seems
There are many natural variations in the sex chromosomes. This can also affect visible sexual characteristics, such as the genitals – here too there are various gradations between the fully formed penis and the visible external part of the clitoris.
Individuals who do not clearly fit into one of the binary sexes refer to themselves as intersex – a group that makes up 1.7% of the world’s population, according to United Nations estimates. This number is comparable to the number of red-haired people in the world.
Since 2018, intersex newborns have been able to register as “diverse” in Germany. Other countries, such as Australia, Bangladesh and India, also recognize a third sex. In Brazil, there are isolated cases of adults who have managed to register as non-binary.
Sex can also change over the course of a lifetime—or more precisely, gonadal sexual identity can change. Chinese researchers found this in a study of mice.
The genes responsible for this change are DMRT1 and FOXL2, which normally balance the development of ovaries and testes in a kind of yin-yang relationship. Changing these genes can lead to a change in the gonadal sexual phenotype even in adult animals.
The role of hormones
Testosterone = male hormone. Estrogen and progesterone = female hormones. That’s what they teach you in school – but again, things are not that simple.
Everyone, regardless of gender, has these sex hormones in their bodies. Average levels of progesterone and estradiol (the most potent natural estrogen) barely differ between men and women.
If one is looking for a binary in hormone levels, one should distinguish between “pregnant” and “not pregnant,” according to an American study of recognized sex characteristics, entitled The future of sex and gender in psychology: Five challenges to the gender binary. The authors show that only pregnant women have extraordinarily different levels of estradiol and progesterone from other people.
Children do not have a significant difference in sex hormones. Only during puberty do testosterone levels increase, so that men, on average, have more testosterone than women.
However, recent scientific discoveries indicate that this difference was also overestimated for a long time due to a methodological flaw, as testosterone was stereotypically studied only in men and estrogens only in women.
Today, specific research is being conducted on the hormonal similarities between the sexes. It has also been discovered that hormone levels depend remarkably on external factors and are not, as previously assumed, purely genetically predetermined.
Expectant fathers, for example, have less testosterone during their partner’s pregnancy. On the other hand, the production of the supposed female hormones estradiol and progesterone is higher when individuals compete for dominance – a behavior traditionally associated with masculinity.
Does the brain have a gender?
The brains of men and women have some differences. Theirs are larger, on average. Brain regions also differ in average size, density of connections, and type and number of receptors.
However, once again, researchers cannot accurately identify the male or female brain. Each brain is quite unique and resembles more of a mosaic with different “male” and “female” parts.
At least that’s what researchers from Tel Aviv University claim in the study Sex beyond the genitalia: The human brain mosaic. The study, carried out with 1,400 brains, indicates that 25% to 50% of them exhibited this mixture of “male” and “female” parts.
This also applies to the brains of trans people, which are being studied in more targeted ways. Different brain regions of these people are sometimes closer to their perceived gender and sometimes to the gender they were assigned at birth.
The fact is: there is no pure binary of sexual characteristics. Any supposedly “biological” arguments in this direction are not in line with what science knows today.
Sex and gender are issues as complex and versatile as humans (and mice and other animals) are.
This article was originally published in German on March 31, 2021 and updated on August 3, 2024.
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