A group letter to the presidents of three evolution/ecology societies objecting to their characterization of sex as a spectrum in humans and all other species

As I reported recently, the Presidents of three organismal-biology societies, the Society for the Study of Evolution (SSE), the American Society of Naturalists (ASN) and the Society of Systematic Biologists (SSB) sent a declaration addressed to President Trump and all the members of Congress. Implicitly claiming that its sentiments were endorsed by the 3500 members of the societies, the declaration also claimed that there is a scientific consensus on the definition of sex, and that is that sex is NOT binary but rather some unspecified but multivariate combination of different traits, a definition that makes sex a continuum or spectrum—and in all species! The bolding below is mine:

Scientific consensus defines sex in humans as a biological construct that relies on a combination of chromosomes, hormonal balances, and the resulting expression of gonads, external genitalia and secondary sex characteristics. There is variation in all these biological attributes that make up sex. Accordingly, sex (and gendered expression) is not a binary trait. While some aspects of sex are bimodal, variation along the continuum of male to female is well documented in humans through hundreds of scientific articles. Such variation is observed at both the genetic level and at the individual level (including hormone levels, secondary sexual characteristics, as well as genital morphology). Beyond the incorrect claim that science backs up a simple binary definition of sex, the lived experience of people clearly demonstrates that the genetic composition at conception does not define one’s identity. Rather, sex and gender result from the interplay of genetics and environment. Such diversity is a hallmark of biological species, including humans.

A number of biologists I talked to had strong objections to both this wonky declaration, which of course is based not on biology but on ideology (see my posts here and here), as well as to its implication that biologists, including members of the three societies, generally agreed with it. But the societies did not poll their members before issuing a general statement in their name!

The statement is in fact is a prime but embarrassing example of societies being ideologically captured to the extent that they misrepresent science to cater to “progressive” liberalism. The object of course is not foxes, horses, or oak trees, but humans; this is meant to reassure people who feel that they are “nonbinary” in gender that nature is just like them. (For an excellent analysis of the issue, and a defense of the binary nature of sex, see Richard Dawkins’s article here.)

Luana Maroja of Williams College, my frequent partner in crime, was even more incensed, and so she penned a letter which she sent last night to the Presidents of the three societies.  With a little help from me, she managed to get 23 biologists to sign the letter (as expected, many demurred and wouldn’t sign). I reproduce Luana’s letter below with permission; Except for Luana and me, I have left off the signers’ names because I didn’t ask them if they wanted to go public about such a touchy subject.

To wit:

Dear presidents of the Tri-societies: ASN, SSB and SSE,

We, Tri-society members and/or biologists, are deeply disappointed by your recent letter “Letter to the US President and Congress on the Scientific Understanding of Sex and Gender” issued last Wednesday, Feb 5, 2025, in response to Trump’s executive order “Defending Women From Gender Ideology Extremism And Restoring Biological Truth To The Federal Government”.

While we agree that Trump’s executive orders are misleading, we disagree with your statements about the sex binary and its definition. In animals and plants, binary sex is universally defined by gamete type, even though sexes vary in how they are developmentally determined and phenotypically identified across taxa. Thus, your letter misrepresents the scientific understanding of many members of the Tri-societies.

You state that: “Scientific consensus defines sex in humans as a biological construct that relies on a combination of chromosomes, hormonal balances, and the resulting expression of gonads, external genitalia, and secondary sex characteristics.”

However, we do not see sex as a “construct” and we do not see other mentioned human-specific characteristics, such as “lived experiences” or “[phenotypic] variation along the continuum of male to female”, as having anything to do with the biological definition of sex. While we humans might be unique in having gender identities and certain types of sexual dimorphism, sex applies to us just as it applies to dragonflies, butterflies, or fish – there is no human exceptionalism.   Yes, there are developmental pathologies that cause sterility and there are variations in phenotypic traits related to sexual dimorphism. However, the existence of this variation does not make sex any less binary or more complex, because what defines sex is not a combination of chromosomes or hormonal balances or external genitalia and secondary sex characteristics. The universal biological definition of sex is gamete size.

If you and the signers of this letter do not agree on these points, then the Tri-societies were wrong to speak in our names and claim that there is a scientific consensus without even conducting a survey of society members to see if such a consensus exists. Distorting reality to comply with ideology and using a misleading claim of consensus to give a veneer of scientific authority to your statement does more harm than just misrepresenting our views: it also weakens public trust in science, which has declined rapidly in the last few years. Because of this, scientific societies should stay away from politics as much as possible, except for political issues that directly affect the mission of the society.

Respectfully,

Jerry Coyne, Professor Emeritus, Ecology and Evolution, University of Chicago
Luana S. Maroja, Professor of Biology, Williams College

THE NAMES OF 21 OTHER SIGNERS ARE REDACTED

I doubt the Societies will pay this letter any attention, as they seem to be doubling down on the sex-is-a-spectrum-in-all-species view. This is performative flaunting of virtue that will accomplish nothing.  But we and the other signers want the public to know that this view of biological sex is not held by all biologists, and hardly represents a scientific consensus. (If there is a consensus, it is most likely the gametic definition described by Dawkins.) If you want to write your own letter rather than sign a group effort, the email addressed of two Presidents are given in their letter, and it’s easy to google that of the ASN President. And if you did sign the letter and want that to be public, simply say it in the comments below.

As a former President of the SSE, I am ashamed of what that society has done, and they should be ashamed of themselves for truckling to the latest ideology. They can of course issue statements bearing on issues of evolution, but this one simply distorts the facts. And, as I reported yesterday, the SSE has seen fit to make more general declarations about politics.