[A]lthough we agree that caution should be exercised in discussing biological explanations, we would argue that this is a specific instance of a more general truth, namely that caution should be exercised in discussing any explanations. It is not only biological explanations that can undergird harmful practices. Environmental theories of left-handedness and same-sex sexual orientation, for instance, have been associated with cruel and unnecessary interventions designed to eradicate these innocuous traits. Environmental theories of human sex differences, if taken to extremes, could potentially produce comparable harms. For example, if we assume that sex differences in career choice are necessarily evidence of bias and barriers, and never products of the freely made choices of those best-placed to make them, we may pathologise the decisions of individuals who take a gender-typical path, and enact progressively more coercive practices to eliminate the remaining gaps. Like earlier efforts to force people into the mould of traditional gender stereotypes, such practices may mean that some people are funnelled into careers that do not align well with their interests and inclinations.

I continue to be amazed at how much dust is stirred up by simply asserting the biological observation that, in animals and vacular plants, there are but two sexes, and those sexes are defined by the reproductive equipment they have. Males are “designed” (I’m speaking teleologically: “evolved” is what I mean) to make small, mobile gametes, and females to make big immobile ones. For decades this has been uncontroversial: A truth universally acknowledged, to paraphrase Jane Austen.
Now, however, for reasons known best to themselves, a small but vocal group of ideologues is denying the sex binary. In my coauthored paper coming out in late June, we hazard some guesses, but those of you following the controversy probably realize that it involves trying to impose one’s ideological views onto nature.
This doesn’t work so easily with the sex binary, as even nonscientists can observe it with their own eyes. The result is that deniers of that binary, such as Agustín Fuentes and Laura Helmuth (editor of Scientific American who’s published several pieces denying a sex binary), face considerable pushback from both scientists—who work with male and female organisms—and “regular” people, who have eyes to see and neurons to analyze.

The dilemma of traditional sex research lay in the unconscious, but unquestioningly assumed division into opposing drives and hereditary factors... The division into heterosexuality and homosexuality, into heterosexuals and homosexuals, is also an artifact that rests on a grave error, namely, on the assumption that a fundamentally different model is necessary to explain heterosexual and homosexual behavior. The entire investigation of etiology was ideologically loaded beforehand because it separated a segment of the sexual continuum and attempted to make analyses with the help of fundamentally different concepts.

All existence seemed to be based on duality, on contrast. Either one was a man or one was a woman, either a wanderer or sedentary burgher, either a thinking person or a feeling person-no one could breathe in at the same time as he breathed out, be a man as well as a woman, experience freedom as well as order, combine instinct and mind. One always had to pay for one with the loss of the other, and one thing was always just as important and desirable as the other.

I am convinced that the species humanity embraces the double species man and woman; that the essence of the complete human being is characterized by this duality; and that the entire structure of the essence demonstrates the specific character. There is a difference, not only in body structure and in particular physiological functions, but also in the entire corporeal life.

Gender discrimination has had a twofold destructive effect on society. Firstly, it has opened society to slavery; second, all other forms of enslavement have been implemented on the basis of housewifisation

A serious difficulty in understanding how to educate and regulate the relations of sex arises from the fact that it is the relation of two equal but distinct halves of the human race, and exists in the dual form—male and female. Unless the distinctive characteristics and requirements of each of these equal halves are fully understood, the relation between them cannot be satisfactory.

create a totally androgynous (and manipulable) world where men and women would become virtually indistinguishable.

My stress on the truth in sexual stereotypes and on the biologic basis of sex differences is sure to cause controversy.

… I argued that the biological determinism in much of Western thought stems from the application of biological explanations in accounting for social hierarchies. This in turn has led to the construction of the social world with biological building blocks. Thus the social and the biological are thoroughly intertwined. This worldview is manifested in male-dominant gender discourses, discourses in which female biological differences are used to explain female sociopolitical disadvantages. The conception of biology as being ‘everywhere’ makes it possible to use it as an explanation in any realm, whether it is directly implicated or not. Whether the question is why women should not vote or why they breast-feed babies, the explanation is one and the same: they are biologically predisposed.

Male and female represent the two sides of the great radical dualism. But, in fact, they are perpetually passing into one another. Fluid hardens to solid, solid rushes to fluid. There is no wholly masculine man, no purely feminine woman. History jeers at the attempts of physiologists to bind great original laws by the forms which flow from them. They make a rule; they say from observation what can and cannot be. In vain! Nature provides exceptions to every rule. She sends women to battle, and sets Hercules spinning; she enables women to bear immense burdens, cold, and frost; she enables the man, who feels maternal love, to nourish his infant like a mother.

That the principle which regulates the existing social relations between the two sexes — the legal subordination of one sex to the other — is wrong in itself, and now one of the chief hindrances to human improvement; and that it ought to be replaced by a principle of perfect equality, admitting no power or privilege on the one side, nor disability on the other.

“The fact that biological sex did not always correspond to ideological gender meant that women could play roles usually monopolized by men, or be classified as 'males' in terms of power and authority over others. As such roles were not rigidly masculinized or feminized, no stigma was attached to breaking gender rules. Furthermore, the presence of an all-embracing goddess-focused religion favoured the acceptance of women in statuses and roles of authority and power.

When it comes to the traits we consider most important in a long-term mate, human beings are largely monomorphic. This is one of the most significant findings of these studies; however, it is easily overlooked when the discussion becomes fixated on traits that people consider less important but where sex differences are found. By shining a spotlight on these traits, we may create an inaccurate picture of our species, even though the differences are real. Our picture of human nature may be built on a foundation of exceptions to the rule. The rule — the fact that males and females in our species are surprisingly similar in many ways — may be relegated to the background. By taking genuine differences and then exaggerating their importance, our picture of our evolved nature may become a caricature: It may contain a recognizable grain of truth but distort its object.