In August 2006, at the general assembly of the International Astronomical Union in Prague, astronomers voted on a new definition of a planet, and Pluto was demoted.
Pluto didn’t change, only its definition.
Now New Zealand’s parliament is preparing to vote on the legal definition of “man” and “woman”. If scientists couldn’t end the controversy over what counts as a planet, why should we expect politicians to define who counts as a woman or man?
There is something strange about deciding what something, or who somebody, is by counting votes. The result was awkward enough when scientists were voting in a domain where they knew what they were talking about.
The planet vote didn’t settle the debate at the time, nor nearly two decades later.
And now we want to do the same with humans?
The Legislation (Definitions of Woman and Man) Amendment Bill was introduced by New Zealand First MP Jenny Marcroft and passed its first reading on May 20. It asks parliament to define woman in law as “an adult human biological female” and man as “an adult human biological male”.
The bill assumes there is a settled biological test for whether a person is female or male – one the law can simply borrow and apply. Marcroft thus frames the change as restoring “biological reality” to the law.
But there isn’t a single biological test, and the bill does not specify one. Instead, biology is messier, more qualified and less politically useful.
When chromosomes don’t match what you see
The test that determines what gets written on a birth certificate is a visual inspection of newborn genitals. This works for most births but not all.
It misses out on the variations where external anatomy appears typical for one sex but internal organs don’t match, and it breaks down when what’s visible doesn’t clearly fit either category.
Chromosomes can be used as a more objective test. But while having a Y chromosome makes you male most of the time, there are too many exceptions and also diversity across species.
The production of gametes (sperm and eggs) offers a more stable definition, but it doesn’t substantiate the definition expected in the bill, because boys and older people don’t produce gametes. Nor do people with conditions where they either don’t produce gametes at all or their gametes don’t match the visual test.
Take gametes seriously for a moment. Does “biological female” mean producing eggs? If it does, then women past menopause are not female under the definition – yet they are a large part of the constituency the bill claims to defend.
The bill either excludes them, or it relies on a looser notion, something like a developmental pathway toward egg production or a phenotype historically associated with female reproductive function. At that point the word “biological” is no longer doing the crisp, settling work the bill needs it to do.
Promising clarity, delivering the opposite
The age clause produces a parallel problem at the other end of life.
A girl, on the bill’s definition, is not a woman. Existing legislation that uses “women” to cover both adults and children breaks and would have to be patched with a new vocabulary of “female children” or something else.
Attorney-General Chris Bishop flagged this, warning of “discrimination on the basis of age”.
Labour opposition MP Camila Belich gave the clearest example. New Zealand’s abortion law refers to “women” and where a statute does not specify an age of maturity, the default is 20. Under the bill as drafted, women under 20 may lose access to abortion.
The bill promises clarity but generates a definitional mess. So why pass it? ACT’s Karen Chhour said the bill was not about science, but about whether ordinary people are “allowed to trust their own eyes, speak honestly”.
Take her at her word. The bill isn’t resting on biology but on the social intuition that everyone knows what a woman or a man is and on the wish to have that intuition ratified somewhere durable.
This is a piece of legislation that treats a complex cluster of biological traits as if it were one settled thing, and ties legal meaning to the pretence.
Which brings us back to Pluto. Its reclassification was harmless because Pluto doesn’t care. It will continue its gravitational dance with other celestial bodies regardless of humans calling it a planet or not.
But women and men aren’t planets. The bill’s reclassification tells people whose lives will be deeply affected by the definition that the question has been resolved.
It hasn’t. And it cannot be resolved by a vote in parliament any more than the nature of Pluto could be resolved by a vote at a scientific conference.
If you have to legislate the meaning of woman and man, you have already admitted the word was doing more than describing biology.
