Comment: NZ First MP Jenny Marcroft’s bill to legally define the words ‘woman’ and ‘man’ is before a select committee with submissions closing July 2. As widely reported, the bill proposes defining woman as an “adult human biological female” and man as an “adult human biological male”.
Marcroft says the bill has been designed to “uphold legal certainty, protect the integrity of sex-based rights, and ensure that language in law reflects biological reality”. However, this language of “biological reality” has little basis in modern scientific understandings of sex.
Biological sex determination is notoriously intricate, with a complicated scientific history. The two-sex model was originally adopted by 18th century European scientists, despite its shortcomings (namely that it was rife with exceptions), because it aligned with social ideals of the time. These held that the female body was the bodily “other” of the male, reflecting culturally and religiously pervasive narratives.
Before that, men and women in the Western world were typically understood as specific manifestations of the same sex; elsewhere, including in Aotearoa, Indigenous communities held a variety of understandings of gender that did not necessarily conform to sex-associated binaries.
In 1905, human sex chromosomes were discovered by scientists, with one pair, XX, allocated to women and another, XY, to men. Culturally dominant understandings assume an alignment between these chromosomes and sexual anatomy and physiology. Such assumptions underlie Marcroft’s bill.
But biological reality is far more complex, routinely challenging rigid impositions with creativity and chaos, something scientists are increasingly reckoning with.
During foetal development in humans, early genetic expression favours the development of female traits because everybody inherits at least one X chromosome. In the standard two-sex model, people with a second X chromosome continue developing female traits. For those who inherit a Y chromosome, relevant genes kick in to sway development towards male traits, preventing, for example, the formation of ovaries in favour of a pair of testes.
However, one issue with the two-sex model at the chromosomal level is that some people don’t have two chromosomes. Possession of up to three (e.g., XXY, XYY, or XXX), four, or even five sex chromosomes is possible, with some people only possessing one (e.g., X). These variations can have diverse effects on traits including height, physical anatomy, or fertility. Importantly, some people are not visibly affected whatsoever.
There are up to 40 different variations from the ‘two-sex model’ … representing about 2.3% of the population. That is a roughly similar percentage to the number of people with red hair in Aotearoa.
Further complications with the two-sex model arise at the genetic level. By the end of the 20th century, scientists had come to understand it was a specific genetic region of the Y chromosome called the SRY region, and not the whole chromosome itself, that induced development of male sexual traits. This meant a person could have a Y chromosome, but, without an operative SRY region on that chromosome, they would likely develop female sexual traits.
With very few of us sure of our exact chromosomal makeup, how can we know what our so-called “biological sex” really is?
According to a Danish study, one in 15,000 people with female anatomy are in possession of XY chromosomes because their SRY region was never capable of switching development towards male traits. In other cases, people who do have functioning SRY regions on their Y chromosome still develop female sexual traits because their foetal cells were incapable of responding to the hormones that would instigate male development.
The science of sexual determination is therefore not linear. It is made up of layers – genetic, chromosomal, hormonal, anatomical, and physiological – that compete with each other at different places in the body at different points in time.
There are up to 40 different variations from the ‘two-sex model’ that can produce alternative configurations in a person’s sexual chromosomes, hormones, and anatomy, which Intersex Aotearoa says represents about 2.3 percent of the population. For context, that is a roughly similar percentage to the number of people with red hair in Aotearoa.
Far from an immutable reality, so-called biological sex is more a constant negotiation that defies the logic of simple binaries. Given this scientific complexity, Marcroft’s bill and its supporters’ claims about “biological reality” cannot go unquestioned. Their mobilisation of scientific terminology invokes not just the authority we commonly associate with the sciences, but also a uniquely privileged claim about what (and who) is or is not designated as natural. In doing so, the bill’s proponents join a long and sordid history – from race science to eugenics – of dehumanisation disguised as scientific classification.
Scientists have increasingly come to understand sex as a spectrum, rejecting the two-sex model’s neat categorisation that the bill is now attempting to put into law. We must, therefore, identify what its façade of scientific authority is attempting to conceal: the bill is the result of political agency, prescribing reductive understandings of “biological reality” by force of law in ways that produce institutional discrimination against trans, intersex, non-binary, and takatāpui communities.
If biological sex were so obviously natural, so universally experienced that it goes without question, it would not need to be maintained, stabilised, and enforced by paternalistic policy.
