If anyone can choose to be female, what happens to women’s rights?

Is your legal sex something that should be easy to change?

Alex Drummond is a transgender woman who lives in Britain. Drummond, 54, does not take hormones, has not had sex reassignment surgery, and has even kept her beard (she says she’s “widening the bandwidth of how to be a woman”).

If a person’s legal sex should track her biological sex, then Drummond’s legal sex should be male. After all, there’s nothing to distinguish her from males except how she sees herself. If a person’s legal sex should track something else, then perhaps Drummond’s legal sex could be female.

Britain, the US and New Zealand are dealing with proposed changes to legislation that make a person’s legal sex a matter of self-identification (although New Zealand First MP Tracey Martin has announced her controversial bill to enable this would be deferred, in light of a failure to properly consult over it). This means that to change sex, one simply fills out a statutory declaration. It will be up to us to decide our sex. But is your legal sex something that should be this easy to change?

Some believe it will help transgender people avoid depending on doctors and other professionals for recognition. Opponents object, insisting that legal sex is crucial for protecting women’s sex-based rights, and those rights are different to those needed to protect transgender people.

In Britain, the government consulted on reforms to the Gender Recognition Act 2004, during which time there was fierce debate between those in favour of sex self-identification and those opposed. Campaigners against reforms to the GRA are worried about sex-based rights and female-only provisions such as shelters, sporting categories, health services and changing rooms.

In the US, the proposed Equality Act involves an expansion of the 1964 Civil Rights Act’s definition of sex to include gender identity, a person’s subjective feeling about their own sex. This turns the single-sex category “woman” (protected because of historical sex inequality) into a unisex category.

In not one of these countries has it been made clear how these changes will interact with women’s existing sex-based rights.

Things are a little different in Australia. In six out of eight states and territories, legal change of sex requires sex reassignment surgery; in two it requires only “clinical treatment” — for example, counselling sessions.

But a proposal in Victoria in 2016, and more recently in Tasmania (ongoing), supports removing information about sex from birth certificates entirely.

This is not sex self-identification in the form it takes elsewhere. Rather, it seems to be a more radical proposal to make no recognition of sex the legal default.

The proposal allows individuals to apply for a recognition-of-sex certificate, if they want one.

Just this week in The Australian it was reported that the University of NSW is giving mandatory training to student club executives, a perfect score requiring them to answer “false” to the statement “your gender is assigned based on your biology and your sex is assumed from your gender”.

Reassuringly, the Morrison government has pledged to intervene to reverse any such move by state governments to erase sex from birth certificates.

If we don’t recognise sex differences in law, then we cannot offer any legal protections on the basis of sex.

In Australia, that will require reform of the Sex Discrimination Act 1984 that protects both sex and gender identity.

If we do recognise sex differences in law but these track something other than biological sex, then the legal protections we can offer might be confused, weakened, or distorted.

How do we prevent discrimination against female employees in male-dominated fields if we can only compare the outcomes of two mixed-sex groups (“women”, comprising female and male people who identify as female, and “men”, comprising male and female people who identify as male)? And what becomes of female sports?

Women’s groups across Britain, the US, Australia and New Zealand are organising in an attempt to thwart the introduction of sex self-identification.

They say that “female” is not a subjective feeling, it’s a set of biological characteristics that a group of people shares, and which make a difference to how those people’s lives go. Females are subject to a range of negative social outcomes — violence against women and girls, workforce participation, economic security — which it is a priority of the Australian government to address.

Given its prominence in other countries, sex self-identification is sure to be on our national agenda in some form soon enough. When it comes, Australians should be ready to stand up for women.

Holly Lawford-Smith is a senior lecturer in political philosophy at the University of Melbourne.