On Sex and Gender Identity: Perspectives from Biology, Neuroscience and Philosophy
by Laeti Harris, Louise Moody, and Pam Thompson
This essay will explore the material qualities and political significance of the sexed human body, which has evolved in the service of sexual reproduction, although is not limited to that purpose. Our exploration is motivated by the relatively recent emergence in western cultures of campaigns to replace the position of sex in social and political spheres with the notion of gender identity, a phenomenon related to how a person feels about their sex (i.e., male, female, both, or neither), which does not depend, in any significant sense, upon their anatomy.
Increasing numbers of people believe that their experienced gender identity is not the same as, or congruent with, their anatomical sex and refer to themselves as transgender, or trans. Being trans was recently amended from being officially recognised as a mental health condition, when in 2018, the World Health Organisation moved gender incongruence from the ‘Mental Health’ of the updated International Classification of Diseases (ICD-11) to a newly created chapter, ‘Sexual Health’, with the stated aim of reducing stigma and increasing social acceptance of trans people. Nevertheless, trans people often suffer from dysphoria regarding the sex of their bodies (often referred to as gender dysphoria), a condition that compels the person affected to live, and attempt to present, as the gender associated with the opposite sex, treatments for which include cross sex hormones and sex reassignment surgery. The rise in numbers of people describing themselves as trans has been accompanied by a pressure for, and considerable success in achieving, social and political change to recognise and eliminate the specific prejudices experienced by trans people.
For instance, in 2004 the UK granted legal recognition to people diagnosed with gender dysphoria allowing them to gain recognition of their preferred gender for all legal purposes such as on their birth certificate. Sixteen years later things have changed dramatically. Trans status has been de-medicalised, and a diagnosis of gender dysphoria is no longer required to be considered transgender with self-identification being sufficient.
If the proposed self-identification (self-ID) legislation is endorsed in Scotland and the rest of the UK, anyone who feels they are the opposite gender will be granted a Gender Recognition Certificate (GRC), without needing any medical assessment or making lifestyle changes, let alone medical or surgical treatments, and will be considered legally to be of the other sex. The rationale is that a person’s gender identity is not automatically connected to their birth sex and that this disconnect, rather than being the result of a neurological disorder, is in fact the expression of “true gender” overriding bodily sex; that is, trans women and trans men are true women and men, respectively, in the wrong bodies rather than dysphoric men/women.
Proponents of gender identity ideology (GI) often make at least four substantive claims: namely:
 Gender identity supersedes a person’s biological sex; i.e. a person’s feelings, rather than their biological sex, is what metaphysically makes someone a man, woman, both, or perhaps neither.
 Sex is not dimorphic (i.e. humans cannot be naturally divided into male and female categories) but is a spectrum or continuum, ranging from men to women and masculine to feminine.
 Transgender people have brains that more resemble their felt, rather than their biological, sex, i.e. a biological man who reports a female gender identity will have a brain with characteristics that are predominant in biological women.
 Transgender people cannot be mistaken about their gender identity, even when they are observably of the opposite sex to that they believe themselves to be; i.e. gender identity is a special kind of mental state, the nature of which one cannot be wrong about.
In §1 we reject  on the grounds that our current understanding of reproductive biology supports the binary classification of biological sex as either male or female: there is no other sex, and no continuum in the reproductive function of sex. The sex-spectrum model is at best descriptive and holds no explanatory power as to the function of sex, and how DSDs can arise as atypical developmental paths along the either male or female track. In §2, we reject  on the grounds that (a) individuals with diagnosis of gender dysphoria display a largely sex-typical brain anatomy and connectivity with a specific neurological signature in the area involved in body perception and ownership, which can often be generated by trauma and socialisation, and (b) complex and multifaceted behaviours and identities are not straightforwardly rooted in the male- or female-typical structure of the brain. There is no biologically prescribed, innate gender identity. Finally, in §3 we reject  on the grounds that there is no non-arbitrary criteria which (a) enables us to distinguish gender identity from other cases in which an individual reports a strongly felt sense or experience of being something that they cannot objectively be, and (b) explains how we can sometimes be radically mistaken about the true nature of our other mental states – e.g. beliefs, memories, and perceptual experiences – but cannot be radically mistaken about the true nature of our gender identity. The conjunction of these considerations from evolutionary and developmental biology, neuroscience, and philosophy then, we contend, constitute strong reasons for also rejecting . We conclude that transgender people are entitled to respect, equal rights, and protection from violence and discrimination as transgender individuals, but they are not objectively members of the opposite sex to that which they were born. Society needs to cater for the specific needs of the transgender population, without encroaching on the rights and needs of others.
Is human sex a spectrum?
At the most basic level, sex is a form of reproduction involving fusion of the genomes of two individuals of the same species and is thought to have evolved as a mechanism to increase genetic diversity, which can confer survival advantages under specific environmental conditions. Sex is commonly thought of as involving the pairing of females and males; where females are types within a species that produce large immobile gametes (eggs) and males are those that produce small mobile gametes (sperm). Indeed, the vast majority of complex multicellular organisms do exhibit this type of dichotomy in gamete size, known as anisogamy, which, in turn, has led to the evolution of genitalia and secondary sex characteristics, observed in humans as the anatomical differences between male and female people. Interestingly, gamete dimorphism is almost ubiquitous in complex multicellular eukaryotes. There are typically only two gametes and two sexes, and this is a highly evolutionarily conserved phenomenon.
In mammals, sex characteristics are determined by the X/Y chromosome system. However, many disparate sex determination mechanisms have evolved independently. For example, many reptiles and fish exhibit temperature-dependent sex determination, whereas in some insects (e.g., bees, ants, and wasps) it is the ploidy state (i.e., the number of sets of chromosomes) that determines whether an individual will be male or female, with males developing from unfertilized eggs with only a single set of chromosomes and females from fertilized eggs with a set of chromosomes from each parent. (Bachtrog et al., 2014) Hence, the emergence of two and only two sexes appears to be evolutionarily fundamental and independent of the mechanism through which the two sexes are specified.
In many simple, single-cell organisms, sexual reproduction can occur without a difference in gamete size or associated separate male and female type organisms. Such ‘isogamy’ is considered the ancestral state; hence, anisogamous organisms likely evolved from an isogamous ancestor. Therefore, understanding why there are male and female types within species requires insight into evolutionary transitions from isogamy to anisogamy. Although isogamous reproduction involves two gametes of similar size, it also ubiquitously requires mating types, a term describing genetically encoded systems controlling gamete compatibility. The most common number of mating types within a species is two (referred to as + and –), but there can be more; from three in the amoeba, Dictyostelium discoideum (Douglas et al., 2016), to thousands in some types of fungi (Billiard et al., 2010), in which sex could reasonably be described as a continuum.
Research into why two (rather than four, five, seven, or twenty) sexes appears to be the near-universal outcome of the evolutionary trajectory from isogamy to anisogamy has most frequently been conducted using mathematical modelling. A dominant hypothesis emerging from these modelling experiments is that the evolution of anisogamy can be explained by gamete competition. Various modelling approaches, including computer simulations, game theory, and population genetics show that a large population of parents with variable gamete sizes will evolve into a stably anisogamous population over a number of generations, with only the smallest and largest gametes remaining. This is because parents producing large (female-type) gametes generate zygotes that survive well, while those that produce many small (male-type) gametes ‘capture’ most of the large gametes. Hence, these models likely explain both why different sized gametes evolve and why there are exactly two sexes. This evolutionary mechanism driving asymmetry in gamete size also fundamentally underlies all of the sexually dimorphic features observed in anisogamous organisms such as mammals, including humans. (Lehtonen and Parker, 2014) Humans produce two gametes, eggs and sperm, and have evolved complex genital and secondary sex differences associated with this type of reproduction.
Human sexual development
Of course, when we discuss the sex of a person, we are talking about more than their ability (or otherwise) to produce a certain type of gamete. In humans, “biological sex” is also a scientific description of the reproductive anatomies (gonads, and internal and external genitalia) that have evolved to fulfill the function of sexual reproduction. In addressing the assertion that human sex is a spectrum, it is important to emphasize that male and female reproductive anatomies differ qualitatively, as a consequence of arising from differing developmental pathways, rather than quantitatively. There are two sequential stages in typical human sexual development: determination and differentiation. Determination refers to the genetically controlled mechanisms underlying development of a bipotential gonad into either the female or male gonad and begins at 6–8 weeks after conception. This is when expression of the Y chromosome-encoded male sex specifying gene, SRY, is upregulated to promote testis development, while activation of WNT4 and RSPO1 signalling regulate development of the ovaries. (Reviewed in Arboleda et al., 2014) During differentiation, hormones secreted by the testes guide the emergence of the male genitalia, while removing the Müllerian ducts, embryonic structures that develop into the female internal genitalia.
Atypical human sexual development
The arguments of those insisting that ‘sex is a spectrum’ generally rely to some extent on the existence of people with atypical sexual development, while they fail to address the evolutionary function of sex. The 2006 Consensus Statement on Management of Intersex Disorders (Lee et al., 2006) recommended the use of the term disorders of sexual development (DSDs), describe people with atypical sexual development defined as: “congenital conditions in which development of chromosomal, gonadal, or anatomic sex is atypical.” DSDs are also often referred to as intersex conditions, although the two terms are not strictly interchangeable. For example, Arboleda et al. (2014) state:
The distinction and clarification of the terms DSD and intersex is important and necessary. The term DSD was introduced to emphasize underlying genetic and hormonal factors responsible for atypical somatic sex development. However, there are individuals with DSDs who have assumed the term intersex as an identity and reject the notion that the human body must be dichotomous. These individuals view the term DSD as a negative label that implies that atypical sex anatomy must be corrected with surgical or hormonal interventions. Supporters of this position recognize that some interventions may be necessary to maintain physical health, such as removal of dysgenetic gonads in patients at high risk for malignancy but call for a clear distinction between what is medically necessary versus what is elective or cosmetic.
DSDs represent an enormously wide variety of different conditions, some of which are associated with other health issues. While there are individuals who have characteristics of both males and females, most DSDs affect either males or females specifically. Using the 2006 Consensus Statement definition, the incidence of DSD is approximately 1 person per 100 (Arboleda et al., 2014), and this relatively high prevalence has been widely used as evidence for the assertion that sex is a spectrum. The 1 in 100 figure is based on classification of DSDs to include all anomalies of the reproductive organs, but in the vast majority of cases, there is no doubt about the sex of an individual. Hence, while 1 in 100 individuals has some form of DSD, the incidence of those specific types of DSD leading to any ambiguity about an individual’s sex is substantially lower at approximately 0.02% (1 in 5000), and those individuals with ambiguous anatomies may have both male and female traits, not phenotypes representing other sexes altogether. (See https://www.dsdfamilies.org/parents/what-dsd/brief-overview/conditions)
In conclusion, reproductive anatomies differentiate and mature under the control of genetic and hormonal signals, and measurements of these factors have strong predictive power, but do not define the sex of an individual. Hence, human sex is fundamentally defined by male and female reproductive anatomy. Attempts to recast biological sex as a social construct, which then becomes a matter of chosen individual identity, is scientifically inaccurate, and ignores more than a billion years of sexual reproduction and what we understand about how this fundamentally dichotomous system arose.
Alteration of sexual anatomy and/or gender presentation in people with DSDs
Surgery to alter the appearance and function of the genitals is common for people with those DSDs that cause genital ambiguity and may be performed on infants before they are old enough to consent. While some procedures are medically necessary, operations performed purely to ‘normalise’ genital appearance in children too young to consent can be associated with unacceptable long-term consequences; for example, impairment of sexual function. For these reasons, many DSD advocate groups campaign to ban these types of procedures. Furthermore, some DSDs do not become apparent until a child reaches puberty and can change their apparent sex. For example, deficiencies of 5-α-reductase 2 and 17β-hydroxysteroid dehydrogenase-3, in which children are most often raised as girls, but undergo a masculinizing puberty. Those people with DSDs who undergo physical changes (naturally or through medical intervention) that alter their sex can be considered – and may (or may not) consider themselves – transgender. However, it is not clear how comparable the reasons underlying changes in gender presentation/sexual anatomy among people with DSDs are with those of trans people who alter their gender presentation and/or anatomies in response to gender dysphoria.
A recent large study of gender change and gender dysphoria, including a total of 1040 people with DSDs (women with Turner’s syndrome, n = 325; men with Kleinfelter syndrome, n = 219, women with XY DSD without androgen effects (n = 107) and with androgen effects (n = 63); men with XY DSD (n = 87); and women with 26 XX congenital adrenal hyperplasia (n = 221)) from various European countries (Kreukels et al., 2018) found that, while changes in gender presentation were higher in this group than in the general population, scores on a standard questionnaire for gender dysphoria were well within the range of non-dysphoric controls for all individuals with DSDs, while none reached the score range observed among a population with gender dysphoria referred to gender clinics. This suggests that the reasons underlying changes in gender in people with DSDs differ to those of trans people with gender dysphoria and may be directly related to physical changes of their bodies. Nevertheless, Kreukels et al. note that in their study, 10 of the people with DSDs completing the questionnaire had already changed gender before doing so and indicate that this may have ameliorated any dysphoria they had previously experienced. Further, there was a large percentage of missing data in the questionnaires (24% for the female-specific version and 47% for the male version), raising doubts about the validity of the results. Interestingly, this study also found that 12 study participants (two with complete androgen insensitivity syndrome, two with 17-β- hydroxysteroid dehydrogenase-3, one with 5-α reductase 2, one with complete XY gonadal dysgenesis, and five with Kleinfelter syndrome) did not consider themselves (entirely) male or female, or did not feel that they were male or female at all. Also, six participants had gender identities atypical of their diagnostic group (one individual with Kleinfelter syndrome who considered themselves female and five with XX congenital adrenal hyperplasia who considered themselves male). This paper concludes:
Because gender issues can be a delicate topic, it may be necessary to approach patients in a sensitive way if one suspects problems in this area. In doing so, it is important to realize that not all patients identify as male or female and want to live in typical male or female social roles. Recognizing that gender is a non-binary phenomenon could facilitate satisfaction with one’s gender for people from the entire gender spectrum.
The sentiment that no-one should be expected to conform to gender stereotypes (“typical male or female social roles”) is laudable and should apply to everyone, regardless of whether their anatomical sex is typical or not. Nevertheless, differences in sexual characteristics, which can lead individuals to reject the terms ‘male’ and ‘female’, do not detract from the biological mundanity of humans. We are a sexually dimorphic species, like all other mammals, regardless of ultimate sexual function or dysfunction or how we feel about our bodies. For individuals with reproductive anatomies including both male and female features, sex classification is a complex process with input from medical professionals, parents, and (when they are old enough to understand) patients themselves; however, the anatomical features leading to such ambiguity in sex emerge from the biological processes that produce males and females, there are no additional sexes that produce separate types of gamete, only rare variation within female and male specification.
In conclusion, DSDs do not undermine sex dimorphism in humans. As in all mammals, human sexual anatomy arises as a consequence of anisogamy, a phenomenon invariably associated with only two sexes. There are people with atypical sex organs, however, these demonstrate development along male and/or female paths, and there is no evidence for a third sex. However, anatomy is not all there is to the social concepts of man and woman. Both women and men have assumed/been confined to very different roles in society throughout history and this rift has occurred along the biological line, resulting in the female and male classes with different respective histories, life opportunities, and collective identities. How does the concept of gender identity relate to these gendered roles? What is gender identity exactly? Does it exist only in the realm of ideas? Is it only a set of culturally and temporally variable stereotypes externally imposed, a deeply held feeling about oneself, or is it an intrinsic, essential property of our being? Could gender identity be innate, but different from sex, i.e. grounded in biology but independent of our anatomical sex?
Is it possible to have male brain in a female body (and vice versa)?
Human cultures often tend to conceptualise and explain the world in binary terms (dark/light, idea/matter, hot/cold). The mind/body dichotomy, where the mind is seen as elevated and boundless and the body as lowly, reductive and prone to degradation is one of the oldest western philosophical tropes and one that informs gender identity ideology (GI). If gender identity does not reside unambiguously in our body, it must be an emanation of our mind (brain) and hence supersedes our bodily sex. Notably, some proponent of GI purports that transwomen are biological females because their innate sense of gender is hardwired in the brain, and therefore biologically determined.
Sex differences in brain structure and neural connectivity
Recent progress in neuroscience, in particular the use of MRI technology, shows that there are clear differences between male and female brains in term of structures and functions at neural, neuro-anatomical connectivity and neurochemical specification levels. ((Hines, 2011) and references therein) Such differences arise in utero under the influence of the sex hormone testosterone and are observed in foetuses (Wheelock, Hect et al. 2019) and at birth in mammals. (Hines, 2011) There is good evidence that the level of testosterone produced by the foetus in utero (in rats and monkeys for instance) influences the degree of masculinisation of the brain within and between the sexes.
One recent study in particular mapped neurological connectivity between different parts of the brain in 118 human male and female foetuses in utero from the second half of gestation onwards. (Wheelock, Hect et al. 2019) They showed statistically significant differences between male and female foetuses in the way the lobes and neural networks of the brain are connected. As this study was conducted using subjects before they could have experienced socialisation, it is held as solid proof that males and females start life with significantly different brains. However, whether these original dissimilarities remain throughout people’s life as they become socialised or whether these differences translate into behavioural patterns and identities still remains to be explored (see below).
From birth onwards, humans are a combination of nature and nurture. Therefore, when looking at child and adult brains, it is extremely difficult to distinguish the sex differences pertaining to biology from those caused by socialisation, because neuroplasticity (what makes us efficient learners) means that social interactions and individual experiences can significantly shape the brain. Children are therefore not blank slates, and neither is there any overwhelming biological determinism. (Hines 2011) Male and female humans are socialised differently according to their anatomical sex, arguably amplifying any pre-existing biological male or female traits, such as aggression (encouraged in boys) or nurturing behaviour (encouraged in girls). Socialisation can also generate behavioural or cognitive differences between males and females that have no basis in biology. A good example of this is the observation that the gap in mathematical (and other cognitive) abilities between boys and girls has decreased globally through time and is virtually non-existent in cultures where sexist stereotypes are less intensively enforced. (Guiso, Monte et al. 2008) Therefore, the very structure, connectivity and neurochemistry of the brain is malleable and can be impacted by socialisation from birth. A short-term study, often quoted in the media, revealed that, after just a few weeks of meditation, MRI scans show increases in regional brain grey matter density, illustrating the extraordinary plasticity of our brains. (Hölzel, Carmody et al. 2011)
The transgender brain
If nurture (sexist culture) reinforces nature (biology) in shaping typically male and female brains, how is it conceivable that a minority of people could develop a male (female) brain in a female (male) body as GI claims? Below we mainly examine several case studies looking at the brain of people who have been diagnosed with gender dysphoria (NB: the findings do not apply to the rest of the trans umbrella, as defined by Stonewall UK), including the foundational paper that led to the “brain sex” idea. (Zhou, Hofman et al. 1995)
The volume of the central subdivision of the bed nucleus of the stria terminals (BSTc), a brain area assumed to be essential for sexual behaviour in mammals, has been shown to be larger in males than in females. The foundational paper of the “brain sex” idea found that transgender people have BSTc typical of the other sex and concluded that transwomen have a women’s brain. (Zhou, Hofman et al. 1995) There are several caveats to this work and subsequent supporting studies. (Zhou, Hofman et al. 1995; Bao and Swaab, 2011) The findings are based on a very small number of subjects: only six transgender individuals, including only one female to male transgender person, were examined, and there is an overlap in the BSTs size range within the control population, begging the question whether the results are statistically significant. No systematic control for sexual orientation, which is known to influence the sexual differentiation of the brain, was performed. (Burke, Manzouri et al. 2017) The study was based on post-mortem observations and on a very small, specific area of the brain’s grey matter. The interpretation that the BSTs size is involved in the sexualisation of the brain is based on non-human models and there was no assessment of the impact of socialisation or potential hormonal treatments on the differentiation of the BSTc volume, which arises late in life (puberty), compared to other brain structures.
More recent studies covering a much greater number of patients (Burke, Manzouri et al. 2017; Savic and Aver 2011) show that gender dysphoria has a unique fingerprint in the white matter connectivity, morphometry and structural volumetry of the brain, rather than a sex-atypical signature. In many of the white matter tracts studied by fractional anisotropy (FA) the transgender groups displayed overall (birth) sex-typical patterns, a similar degree of sexual differentiation as observed in homosexuals and a lower sexual differentiation than heterosexuals. (Burke, Manzouri et al. 2017) The lesser sexual differentiation in the brain of homosexual and transgender may be related to testosterone levels during foetal development. Interestingly, several studies that describe FA sex-atypical patterns in the transgender population do not control for sexual orientation. This study does correct the data for sexual orientation and shows that both male and female homosexuals exhibit as much sex-atypical features in selected parts of the brain as the transgender group. Yet homosexuals do not identify as being of the other sex or as having a female (male) brain in a male (female) body. When corrected for sexuality, people with gender dysphoria have a (birth) sex-typical brain but the part of the fronto-occipital track involved in processing body perception in relation to self, body awareness and ownership shows atypical features that neither the heterosexual nor the homosexual control (non-trans) groups possess.
Another study based on MRI scans from eight young transgender men (female at birth) shows that the area of the brain reacting to stimuli to the chest displays a dampened sensory response in transmen compared to female controls (n = 8). (Case, Brang et al. 2017) It is worth noting that this study had no male control group. This study, despite a very low number of participants and no male control group, is often cited to support the premise that trans-men have a male brain. We can argue that, in fact, these findings do not support the conclusion that transmen have a male typical reaction to stimuli and hence a male typical brain. Instead, the results are better explained by the observations and findings cited above that gender dysphoria is caused by atypical body ownership and self-perception in the fronto-occipital part of the brain (see above). (Burke, Manzouri et al. 2017) A more recent study points out that many of the brain-specific differences associated with gender dysphoria are situated in areas dealing with body ownership, distress and social behaviour. All are highly susceptible to be influenced by socialisation and trauma rather than innate. (Gliske, 2019)
All these studies were conducted on participants with diagnosed gender dysphoria. Self-identification of gender is open to people who do not have gender dysphoria and therefore are unlikely to present the specific neurological signature associated with this condition.
The gendered brain: do sex differences in brain structure translate into gendered behaviours?
Despite well-documented innate structural brain differences and the sex-specific early socialisation under which the brain plastically develops, males and females show an extraordinarily large overlap in psychological traits and cognitive types (empathic vs. systemic e.g. (Greenberg, Warrier et al. 2018)). In terms of cognitive abilities, psychology and behavioural expression, studies show that there are no clear male or female brains. One such study conducted in almost half a million people endeavoured to track brain-type differences and the signature of autism by scoring empathy (emotion), sensorial perception and systemizing (analytical) quotients using a simple questionnaire. Despite the complete overlap in the score distribution between male and female controls for these three parameters, the study found a small difference in the sex-specific averages and proceeded to conclude that there are typical female (empathic) and male (analytical) brains. However, what the data truly show is that the distributions are almost identical between men and women, with only a small difference in the modes (score reached by the highest number of people) of these 3 parameters between males and females. This means that the majority of men and women share the same score distribution for these parameters with a slightly increased number of men scoring marginally higher on the systematic quotient and lower on the empathic quotient compared to women. In addition, the finding that females score slightly higher on average for empathy for instance could be due to two factors: 1) the study relies on subjective responses to a coarse questionnaire, therefore the answers are subjective and can be influenced by internalised social expectations and 2) the alleged greater empathy displayed by women on average may be due entirely to socialisation in a world that often expects women to assume caring (empathetic) roles. The empathic- and systemic-type brains exist in both males and females including in their extreme manifestation and the variability observed within a sex is much greater than the average difference between sexes. (Baron-Cohen, Richler et al. 2003, Greenberg, Warrier et al. 2018)
It is reasonable to assume that there is an evolutionary need to favour certain sex-specific behaviours associated with reproduction, such as nurturing behaviours in females and aggressive comportments in males, and that these specific traits are indeed prevalent in the corresponding sex class. However, once again, there is a continuum between males and females with respect to these psychological traits and behaviours (Hines 2011). In addition, these particular behaviours are not necessarily expressed consistently throughout someone’s life and their intensities and manifestation (e.g. in response to puberty or pregnancy) are mediated by natural hormones surges, which activate previously organised, sex-specific neurological systems. For instance, the nurturing behaviour of a new mother has been linked to hormonal changes during and post pregnancy (Glynn, Davis et al. 2016). These traits are transient and linked to people’s biological sex and reproductive roles. They might participate in, but do not constitute, one’s gender identity.
While certain traits are on average slightly more or less pronounced in male or female subjects (e.g. spatial orientation, aggression), individual personalities and identities are the sum of a multitude of traits and proclivities, and any given individual, for any given trait, can score anywhere on the brain-type distribution. Therefore, several publications and meta-studies by Rippon, among others, have described individuals as a patchwork of stereotypically “masculine” and “feminine” traits and challenge the notion of a gendered brain (Rippon 2019). The implication of that analysis is that no single behaviour or cluster of traits are typically and unambiguously male or female, and none can be regarded as a robust marker of femaleness or maleness.
In summary, the assertion that “true” gender is hard-wired in the brain and can be independent of one’s biological sex is doubly defeated by neuroscience. (1) Transgender people (with a diagnosis of gender dysphoria) display a largely sex-typical brain anatomy and connectivity with a specific neurological signature in the area involved in body perception and ownership; they do not have a female (male) brain in a male (female) body. (2) Neuroanatomical sex differences in the brain are most likely linked to sexual and reproductive functions (directly connected to anatomical sex) but they are poor determinants of an individual’s psychological traits, cognitive abilities, professional occupations, taste, interests and behaviours in everyday life, despite early and constant reinforcement by socialisation in largely sexist cultures. In other words, the “sexed brain” (Wheelock, Hect et al. 2019) is a poor predictor of individual identity and personality. Complex and multifaceted identities are not straightforwardly rooted in the male- or female-typical structure of the brain. This does not mean that gender identity can be innately male or female irrespective of one’s biological sex. Rather, what it means is that gender identity is not an inherent (biological) and fixed characteristic of human brains but can only be envisioned and understood as an external, socially constructed phenomenon corresponding to strongly internalised and externalised stereotypes and expectations. It implies that the sense of belonging to a specific gender can only be an identification into externally imposed social conventions, more or less arbitrarily associated to the female or male sex. Society is currently debating whether these externally imposed, temporally and culturally variable stereotypes should constitute the definition of what a man and a woman are, or whether there are still good reasons to use objective, biological differences between males and females as the defining criteria for these two ontological categories.
A philosophical perspective on the perception of one’s gender identity
A natural starting point concerning the concept of gender identity – specifically, in what gender identity might said to essentially consist (in philosophical speak, in what metaphysical ingredient(s) might said to make it up) – is to consider the definition offered by influential organizations such as Stonewall who speak of: “A person’s innate sense of their own gender, whether male, female, or something else, which may or may not correspond to the sex assigned at birth.” (https://www.stonewall.org.uk/help-advice/glossary-terms#g, my emphasis)
A definition that has even filtered down to the NHS who now inform us that: “Biological sex is assigned at birth, depending on the appearance of the genitals. […] Gender identity is the gender that a person “identifies with or feels themselves to be.” (https://www.nhs.uk/conditions/gender-dysphoria/)
These remarks encapsulate the increasingly common thought that gender identity is an intrinsic property of the subject; i.e. a property that constitutively depends in some way upon physical processes and events occurring within the subject. And this intrinsic property, some now say, is sufficient for making someone a certain sex (hence: male bodied people who identify as women are now competing in women’s sports, being housed in women’s prisons and refuges, and can enter other single-sex spaces such as changing rooms). Another way to put it is that gender identity is said to consist in someone’s strongly felt personal conception of themselves as male, female, some combination of both, or perhaps neither. And so, someone’s experienced gender identity is not an externally verifiable characteristic such as their having brown eyes or being six-feet tall, but rather, concerns their inherent sense of being, or feeling strongly aligned with, a certain sex.
Two clarifications are in order before we raise two questions about gender identity. First, we have sidestepped philosophical definitions of gender identity (e.g. McKitrick’s (2015) dispositional account according to which someone’s gender identity consists in them being disposed to behave in certain ways that are perceived as being gendered in their social context or Jenkins’ (2018) norm–relevancy account, according to which someone’s gender identity consists in them experiencing certain gender norms as being relevant to themselves) since such definitions are not currently enshrined in any policies or guidance and so, are not immediately relevant to people’s lives. Second, although we reject the standard conception of gender identity, our aim is a therapeutic one in that a diagnosis of the concept’s most significant flaws can only illuminate those desiderata that any conceptually adequate account of it should meet, with such desiderata naturally being compatible with women’s sex-based rights.
Our first question is this: By what non-arbitrary criteria can we distinguish gender identity from other cases in which someone also reports a strongly felt sense or experience of being something that they cannot objectively be?
The question can be illustrated by considering what are called Delusional Misidentification Syndromes, i.e. psychiatric-neurological syndromes that are characterized by the misidentification of persons, the self, or objects in one’s environment. People with Cotard Syndrome (see e.g. Cotard (1880); Ramirez-Bermudez et al. (2010)), for example, strongly feel that they are missing limbs, internal organs, or are even dead; people with Mirrored-Self Misidentification Syndrome (see e.g. Breen et al. (2001); Coltheart (2001)) strongly feel that their reflection is someone else or themselves at a different age; and people with Clonal Pluralization of the Self (see e.g. Christodoulou (1978); Vörös et al. (2003)) strongly feel that there are multiple physical and psychological copies of themselves. There are thus a range of reasonably well-understood conditions that all involve people reporting strongly feeling that they are something which they just cannot objectively be (trivially, the dead lack mental states, physics dictates that your reflection cannot be your past or future self, and qualitative reduplication belongs in Star Trek). In light of such conditions, we need a plausible explanation of why we should accept:
[A] A strongly felt feeling is sufficient for being a man, woman, blend of both or neither. (Standard Conception of Gender Identity)
[B] A strongly felt feeling is not sufficient for being dead, being reflected as your past or future self in mirrors and being physically and psychologically reduplicated. (Instances of Delusional Misidentification Syndromes)
To be clear: we are not uncharitably saying that someone who reports a mismatch between their experienced gender and biological sex does have a delusional misidentification syndrome. Our point, rather, is that if gender identity consists solely in some type of internal mental state, and if that concept of gender identity is going to inform policies and guidance, then we need a plausible story as to why feelings maketh the man or woman (or perhaps something else) but do not maketh being dead, seeing your past or future self in mirrors, or being magically reduplicated. Conceptual consistency seemingly requires, for example, that someone with Clonal Pluralization of the Self cannot be convicted of murder because a jury could never determine beyond reasonable doubt which ‘copy’ offed Reverend Green in the dining room with a candlestick or that a thirty something hobby cyclist with Mirrored-Self Misidentification Syndrome need only show his significantly older reflection to race officials in order to compete in the seventy plus age group where his chances of winning medals naturally improve. How, then, might we maintain the distinction between [A] and , and so, avoid such absurdities?
Answering this question is not our challenge to meet, still, it is instructive to consider the obvious answer which runs: Gender identity is a well-understood non-clinical phenomenon that does not causally spring from any underlying neuropathologies, but Delusional Misidentification Syndromes are recherché clinical phenomena that causally spring from underlying neuropathologies. Hence, these different aetiologies mean we can consistently accept [A] whilst rejecting [B]. But this answer only clarifies our concern, for it is irrelevant whether someone’s gender identity has some identifiable clinical aetiology. We are simply asking for some positive explanation of how being a man or woman (or some other combination) can be alchemized from strongly felt feelings so that intuitively absurd comparisons can be avoided: simply saying that feelings maketh the man, woman (or some other combination) is not illuminating without some positive explanation of how that alchemization is supposed to occur. We are not denying that no such explanation is available, but until one is given, the politically driven insistence that someone’s affective mental state overrides their objective biological makeup looks remarkably like culturally normalised medieval superstition.
Our second question is this: What justifies the implicit assumption that someone cannot be radically mistaken about their gender identity, when we are often radically mistaken about the true nature of certain other mental states? Plainly put: Why should we charitably assume that someone cannot be radically mistaken about their gender identity, when it is non-controversial that we are often radically mistaken about the true nature of our beliefs, memories, perceptual experiences, and sensations? What we mean by this question can be illustrated by just three examples:
Memories: Consider the well-documented phenomenon of Imagination Inflation (see e.g. Garry & Polaschek 2000; Mazzoni & Memon 2003) in which imaginings are mistaken for genuine memories. Famously, Loftus & Pickrell (1995) found that 5 out of 24 subjects falsely remembered being lost in a shopping mall as a child after being presented with a story to that effect. More worryingly, Shaw & Porter (2015) found that of 30 subjects who had not committed a serious crime as a teenager, 21 (70%) recalled doing so after their interviewer used priming tactics such as presuming knowledge of the event (“[The] details […] have to come from you”). And eyewitness testimony is notoriously unreliable with its dependence upon imperfect visual equipment and the brain’s ability to accurately process, store, and remember perceptual information. Such cases straightforwardly show that, sometimes, we are radically mistaken about the true nature of our memories: sometimes, what strongly seem like genuine experiential memories are really imaginings of events that never occurred at all.
Perceptual Experience: Consider the phenomenon of inattentional blindness (see e.g. Mack, A & Rock, I (1998); Hutchinson (2019)), whereby focusing our attention upon one thing sometimes means that we fail to notice other, unexpected, things. In the famous ‘Invisible Gorilla’ experiment (Simons & Chabris: 1999) around fifty percent of people who were asked to watch a short video of people throwing a basketball and to silently count the number of passes failed to notice a gorilla strolling into the middle of the scene and thumping its chest for nine seconds. Or consider the phenomenon of change blindness (see e.g. Feil & Mestre (2010); Levin et al. (2000)) whereby we sometimes fail to see surprisingly large changes to objects and scenes. In the famous ‘Door’ experiment (Simons & Levin: 1998), nearly fifty percent of people failed to notice the switching of their conversational partner whilst briefly distracted by two people passing between them carrying a door. Such cases straightforwardly show that, sometimes, we are radically mistaken about what we are seeing: seeing simply isn’t believing.
Sensations: Consider the familiar phenomenon of referred pain whereby pain in one part of the body is often experienced as originating from elsewhere: heart attacks are often preceded by episodes of ‘indigestion’, an inflamed gallbladder episodes of ‘shoulder’ pain, and developing pancreatic cancer by episodes of severe ‘back’ pain. Or consider how people with neurological conditions such as Alzheimer’s and epilepsy sometimes report episodes of sensing unexplained tastes and odours. Such cases straightforwardly show that, sometimes, we are radically mistaken about the source, location, and even existence, of our sensations: sometimes, pain is experienced somewhere other than its source, and tastes and odours may not even exist at all.
These considerations suggest a simple argument: Memories, perceptual experiences and sensations are mental states about which we are sometimes radically mistaken; gender identity is said to be one kind of mental state; so, ex hypothesi, people can sometimes be radically mistaken about their gender identity – either concerning certain of its properties (e.g. perhaps the strong feeling that some people call their gender identity is really determined by things outside, rather than inside, the head) or even their having one at all (e.g. perhaps the concept will eventually be unmasked as a fiction that is destined to join the luminiferous aether, phrenology, and the four temperaments in scientific ignominy). Rejecting this argument thus requires showing why gender identity is a special kind of mental state: specifically, our opponent must show how we can consistently accept:
[C] People have infallible introspective access to the true nature of their gender identity. (Commitment of Gender Ideology)
[D] People lack infallible introspective access to the true nature of their mental states, viz. memories, perceptual experiences, and sensations. (Empirical observations)
To be clear: we are not uncharitably saying that someone who reports having a particular gender identity is wrong about having a feeling (curiously, we do seem to have infallible introspective access to the phenomenal ‘what-it-is-like’ aspect of our conscious experiences). Our point, rather, is that if gender identity consists solely in some type of mental state, and if we are sometimes radically mistaken about the true nature of our other mental states, then there is no principled non-arbitrary reason for denying that we are sometimes radically mistaken about the true nature of our gender identity.
We confess to complete puzzlement at how to positively reconcile [C] with [D]. And rather than undertake our opponent’s task, we will conclude by sketching two reasons for scepticism about the standard conception of gender identity, i.e. for scepticism about [C]. The first reason is that (or so it strikes us) many people lack any distinctive innate feeling that might reasonably be called their gender identity. When I confine myself to introspective reflection and ignore what Stonewall and friends claim about gender identity, intuition dictates that there is no distinctive innate feeling that I can identify as being my gender identity  – I simply have a body that is female and that is it (and a mental state that is not consciously accessible is indistinguishable from one that does not exist). Whilst there are, to our knowledge, no studies on the percentage of people who report having a gender identity , my inability to introspectively detect any feeling that might reasonably be called one does not seem obviously unusual or counterintuitive. This scenario is thus a counterexample to [C], since there is at least one person who lacks, or cannot consciously access, anything that might be called a gender identity, viz., me.
The second reason for scepticism about [C] is that people who report having a gender identity, we suggest, are psychologically internalizing restrictive gender roles and stereotypes (e.g. tropes such as ‘only girls wear pink’ and ‘coding is for men’) and then mistaking that internalization for an innate feeling of being male, female (or some other combination). That is, some people are mistaking psychological assimilation of and attitudes towards culturally inculcated gender norms for an innate gender identity. In our story, someone who identifies as a woman has integrated mainly female gender norms into their psyche and then mistaken that integration for an innate feeling of being female, and vice–versa for someone who identifies as a man (someone who identifies as a blend of both will have integrated some proportionate combination of male and female gender norms into their psyche and then mistaken that for an innate feeling of being bigender). Baldly put, we reject [C] on the grounds that some people who report experiencing a particular gender are psychologically confusing externally imposed gender roles and gendered expectations for an innately given feeling inside the head.
It now seems that an adequate defence of the claim that people are not radically mistaken about their gender identity requires two things. First, it must be explained why gender identity is – unlike memories, perceptual experiences, and sensations – an epistemically special mental state (presumably, this will require identifying some property, or properties, that grant us infallible introspective access to its nature). Second, and relatedly, it must be explained how the gendered messages with which people are bombarded do not determine the feeling that they call their gender identity. Until these explanations are given, we urge caution about both the existence and metaphysical significance of an innate gender identity. We submit that, in its current state, the concept of gender identity is a Cartesian fiction that has no serious business informing those policies and guidance that affect our daily lives.
We have marshalled empirical and conceptual considerations from biology (§1), neuroscience (§2), and philosophy (§3) to reject four key tenets that prop up GI. Our current understanding of reproductive biology does not support the idea that biological sex is a spectrum, and therefore, that sex dimorphism is an inaccurate and outdated tool to classify all individuals as males or females. The sex-spectrum model is at best descriptive and holds no explanatory power as to the function of sex and how DSDs can arise as atypical developmental paths along the male or female track. Evidence from neuroscience shows that gender dysphoria has little connection to gender or sex and is likely linked to body perception, socialisation or trauma. It straightforwardly rejects the notion that transgender people can have a male (female) brain in a female (male) body and that gender identity is innate. Evidence from the philosophy of perception arguably shows that the current concept of gender identity is a metaphysically incoherent one that does not rationally ground someone’s beliefs about their own gender. Together, the disciplines of biology, neuroscience, and philosophy plausibly demonstrate that biological sex is what makes us male or female and that the feeling of gender identity is not innate but is a subjective identification with socially constructed markers of masculinity or femininity.
But suppose that any, or all, tenets of GI are true. Does this mean that people should be treated according to their gender identity, rather than observed sex, for political and legal purposes? Our answer is an emphatic no. Social groups and minorities are organized, socialised, and othered in virtue of their possessing certain observable characteristics that are grounded in material reality rather than their self-perception. To our knowledge, young girls are not asked if they feel like boys before being subjected to genital mutilation; trafficked women are not asked if they feel like men before being treated as sexual commodities; and the current U.K Prime Minister did not ask the 70% of his cabinet that are biological men whether they identify as women before appointing them. In an unequal society, where people are treated differently on the basis of recognisable characteristics such as sex, skin colour or age, people must retain the right to politically organise and build their struggle around these characteristics. As such, our conclusion is just this: Because the material reality of biological sex is the only objective criterion that can be used to categorise all individuals as either man or woman, the concept of gender identity should not primarily determine the rights and protections that society grants individuals. Of course rights and protections should be granted to transgender individuals in virtue of the objective nature of the discrimination they face; but, since gender identity is not sufficient for determining someone’s sex, those rights and protections cannot be exactly the same (e.g. they might include ‘third’ spaces such as separate changing facilities or sports categories) as those afforded to women for being females.
Dr. Laeti Harris has a biology background and does academic research in biogeochemistry. Dr. Louise Moody, a gay and lesbian campaigner and activist, received her doctorate in philosophy at York University. She specializes in the metaphysics of perception, and is the founder of Fair HE, an initiative to defend freedom of speech within higher education. Dr. Pam Thompson did academic research on the molecular genetics of human disease at the University of Manchester and currently works from home as a scientific editor.
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 Cf. Gender identity concerns, according to, the American Psychological Association “a person’s internal sense of being male, female or something else” (https://www.apa.org/topics/lgbt/transgender), Amnesty International “the way you identity with and express yourself in masculine and/or feminine notions of identity” (https://www.amnesty.org.uk/lgbt-gay-human-rights-sexual-orientation-gender-identity), the Gender Identity Research and Education Society “[the] psychological identification of oneself [as one or more genders]” (https://www.gires.org.uk/resources/terminology/), the Human Rights Campaign “One’s innermost concept of self as male, female, a blend of both or neither” (https://www.hrc.org/resources/sexual-orientation-and-gender-identity-terminology-and-definitions), and Mermaids “How you, in your head, define your gender” (https://www.mermaidsuk.org.uk/assets/media/Genderbread-Person-3.3-HI-RES.pdf).
 Compare: I can introspectively identify other distinctive feelings such as jealousy, anger, or love.
 In an admittedly unscientific Twitter poll, 93% of 1628 people reported lacking a gender identity (4% reported having one and 3% answered ‘other’).
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