Il neurosessismo è la convinzione errata che cervello maschile e femminile siano biologicamente differenti. Porteremo esempi e relative fonti a sostegno del fatto che questa sia un’idea sbagliata:
- Intervista a Catherine Vidal, direttrice di ricerca all’Institut Pasteur di Parigi:
“È vero che il cervello femminile è mediamente meno grande di quello maschile (1,2 chili contro 1,35) ma non incide sul quoziente di intelligenza: il cervello di Einstein pesava 1,25 chili. La neuroscienziata francese, che ha fondato anche una rete internazionale chiamata Neuroculture-Neurogenre, smonta molti degli studi pubblicati con gran fragore negli ultimi anni. Quello secondo cui le donne avrebbero una migliore capacità di linguaggio oppure sarebbero per forza “multitask” perché capaci di usare i due emisferi cerebrali. Sulle funzioni cognitive, dice Vidal, non è possibile dire che esiste un cervello “maschile” o “femminile”.“Ci sono più differenze tra singole persone dello stesso sesso che tra uomini e donne”. Al di là della pubblicità di cui godono molte pubblicazioni, spiega ancora la neurobiologa francese, il conto è presto fatto: dei 16mila studi con immagini a risonanza magnetica, dal 1992 a oggi, solo il 2,6% ha riscontrato significative differenze sessuali tra i cervelli maschili e femminili.”
- Interviste a diversi esperti:
“Rebecca Jordan-Young, docente ad Harvard, ha analizzato la questione nel saggio intitolato “Brain Storm, i difetti della scienza delle differenze sessuali” (disponibile soltanto in inglese). Per Jordan- Young gli studi che cercano di dimostrare le differenze sessuali basandosi sugli ormoni non soddisfano, nella maggior parte dei casi, gli standard scientifici. Ci sarebbe, infatti, una debolezza metodologica di fondo che rende impossibile pensare che si possano fare esperimenti in cui tutte le variabili sono controllate.””Dello stesso parere è anche Raffaella Rumiati, docente di Neuroscienze cognitive alla Scuola internazionale superiore di studi avanzati (Sissa) di Trieste e autrice di svariate pubblicazioni scientifiche e mainstream, tra cui “Donne e Uomini. Si nasce o si diventa?”. Secondo Rumiati non è chiaro quali siano le eventuali differenze cognitive o comportamentali che corrispondono alle differenze morfologiche tra i cervelli maschile e femminile riportate nella letteratura scientifica. Anche il fatto che le donne abbiano, in genere, un cervello più piccolo degli uomini non implica una riduzione di funzionalità. “La grandezza del cervello è proporzionale al resto del corpo – dice Rumiati. – Sarebbe come dire che le persone basse sono meno intelligenti di quelle alte”.A supportare la tesi di Rumiati c’è un recente saggio di James Flynn, uno dei massimi esperti internazionali di studi sul Qi (Quoziente intellettivo). Flynn dice che negli ultimi cento anni le donne hanno superato gli uomini in fatto di intelligenza, migliorando le prestazioni nei test del Qi. E questo non certo perché i loro geni o le dimensioni del cervello sono cambiate ma perché sono diventante più istruite e hanno raggiunto maggiori possibilità di espressione rispetto al secolo scorso.E allora perché c’è chi continua a insistere nel volere dimostare che esistono differenze biologiche tra i cervelli maschile e femminile e che sono alla base di diversi comportamenti? “Nonostante le critiche e le perplessità – dice Rumiati – negli ultimi dieci anni le neuroscienze hanno esercitato un notevole fascino, come testimonia il proliferare di nuovi campi di indagine con il prefisso neuro-: neuroeconomia, neuroetica, neuro estetica e così via. Anche lo studio delle differenze sessuali ha subito questo fascino a giudicare dall’intrusione nella letteratura sulle differenze di molti termini neuroscientifici per esprimere però dei concetti antiquati e retrivi. Questo fenomeno è particolarmente evidente nei testi divulgativi sulle differenze sessuali”.Un fenomeno che è stato definito dalla scienziata australiana Cordelia Fine con il termine “neurosessismo”. Secondo Fine, il neurosessismo si manifesta per esempio, quando si afferma che le donne sono più portate degli uomini a prendersi cura degli altri. Un’attitudine che è sempre stata considerata “naturale” e che ora si ammanta di un linguaggio scientifico. Oppure quando si dice che le donne non sono portate per la matematica, l’informatica e le materie scientifiche in generale. “Non ci sono prove scientifiche convincenti del fatto che le donne non siano portate per le materie scientifiche – dice Rumiati. – Bisogna quindi arrendersi all’idea che se ci sono poche iscritte nelle facoltà scientifiche e poche docenti donne c’è qualcosa che non funziona nel sistema educativo della maggior parte dei paesi cosiddetti sviluppati.”
- Non tutti gli individui sono nettamente classificabili come “maschi” o “femmine”, anche su basi strettamente biologiche. Ad esempio, i cromosomi che determinano il sesso (X e Y) possono esistere in combinazioni atipiche (come nella sindrome di Klinefelter [XXY]). Ciò rende difficoltoso l’uso del genotipo come mezzo per definire esattamente due generi distinti. Gli individui intersessuati possono avere, per varie e diverse ragioni biologiche, genitali ambigui.Gli aspetti biologici non sono pertanto rilevanti, dato inoltre che il processo di costruzione prende avvio nel linguaggio naturale e nelle categorie che esso plasma tramite il continuo rafforzamento nella mente di ciascuno – ad esempio i pronomi che fanno distinzioni di genere o la ripetizione degli insulti. Nel modello psicologico di Jacques Lacan, la “fase dello specchio” (attorno ai 3 anni, quando un bambino vede sé stesso in uno specchio e crede che l’immagine sia il suo “sé”) e lo sviluppo del linguaggio avvengono approssimativamente nello stesso periodo. Pertanto, è possibile che sia il linguaggio a costruire l’intera idea di sé, come pure le distinzioni di genere/sesso. Anche le idee di Ferdinand de Saussure sulle relazioni segno-significante nel linguaggio vengono usate per dimostrare questo concetto: si mostra infatti come nonostante possano esistere delle verità biologiche, la nostra conoscenza e concettualizzazione è sempre mediata da linguaggio e cultura.
- Risposta al “Paradosso Norvegese”:
In risposta al video di Harald Eia sul cosiddetto paradosso norvegese, si capisce dal video solo una cosa, che non può essere attribuita a somiglianze nei ruoli di genere tra le società o a condizionamenti ambientali anche precoci, ovvero che vi sia una differenza nella visione dei volti tra maschio e femmina.
1^ obiezione: la differenza è statisticamente significativa? E’ stata riprodotta altrove e visto se vi fossero errori sistematici? I risultati correlavano? Un singolo studio infatti non significa nulla, se il risultato non è riproducibile con percentuali simili.
2^ obiezione: una differenza di questo tipo in che modo influenza le funzioni cognitive come l’emotività, l’empatia, la tendenza all’aggressività, l’intelligenza, ecc.? Dato che non le influenza non è una prova di differenze sostanziali tra il cervello maschile e quello femminile nella diversità dei comportamenti.
3^ obiezione: qualora ci fosse questa differenza, sappiamo anche se essa permane o meno in ambiente favorevole o sfavorevole? Non lo sappiamo.
Sappiamo però che di media l’ambiente tende a prevalere sugli aspetti biologici, si è infatti notato che l’ambiente in cui si sviluppa l’esperienza del soggetto ricopre una maggiore importanza rispetto ai fattori genetici per lo sviluppo della personalità (al quale non fanno eccezione alcune malattie legate a ben documentati fattori genetici come il disordine bipolare, alcune forme di ritardo mentale come la sindrome di Down, la schizofrenia).
In generale, inoltre, la ricerca del settore evidenzia come la personalità e le differenze di comportamento siano da attribuire ad apprendimento e condizionamenti od a modelli e imitazione piuttosto che a fattori puramente biologici.
- Utilizzo mistificatorio delle scoperte scientifiche:
In risposta al nuovo articolo sulla differenza nel connettoma tra uomini e donne, la scienziata Cordelia Fine ha risposto:
“One important possibility the authors don’t consider is that their results have more to do with brain size than brain sex. Male brains are, on average, larger than females and a large brain is not simply a smaller brain scaled up.
Larger brains create different sorts of engineering problems and so – to minimise energy demands, wiring costs, and communication times – there may physical reasons for different arrangements in differently sized brains. The results may reflect the different wiring solutions of larger versus smaller brains, rather than sex differences per se.
But also, popular references to women’s brains being designed for social skills and remembering conversations, or male brains for map reading, are utterly misleading.
In an larger earlier study (from which the participants of the PNAS study were a subset), the same research team compellingly demonstrated that the sex differences in the psychological skills they measured – executive control, memory, reasoning, spatial processing, sensorimotor skills, and social cognition – are almost all trivially small.
To give a sense of the huge overlap in behaviour between males and females, of the twenty-six possible comparisons, eleven sex differences were either non-existent, or so small that if you were to select a boy and girl at random and compare their scores on a task, the “right” sex would be superior less than 53% of the time.
Even the much-vaunted female advantage in social cognition, and male advantage in spatial processing, was so modest that a randomly chosen boy would outscore a randomly chosen girl on social cognition – and the girl would outscore the boy on spatial processing – over 40% of the time.
As for map-reading and remembering conversations, these weren’t measured at all.
Yet the authors describe these differences as “pronounced” and as reflecting “behavioural complementarity” – scientific jargon-speak for “men are from Mars, women are from Venus”. Rather than drawing on their impressively rich data-set to empirically test questions about how brain connectivity characteristics relate to behaviour, the authors instead offer untested stereotype-based speculation. Even though, with such considerable overlap in male/female distributions, biological sex is a dismal guide to psychological ability.
Also missing from the study is any mention of experience-dependent brain plasticity. Why?”
- Articolo scientifico del 2010:
“For instance, she points out that only studies that find a difference are published whereas negative results, which may be more common, are not reported. She points out the many interpretation abuses of modern neuroimaging studies. For instance, the brain’s well-documented plasticity means that one cannot interpret the mere presence of an imaging difference as evidence of innate disparity. Fine also discusses abuses of statistical analyses. Often the studies that report sex differences have surprisingly small sample sizes. It is refreshing to read such a critical analysis of this literature, which is lacking in so many of the previous writings on gender differences. […] She concludes that neurosexism promotes damaging, limiting, and potentially self-fulfilling stereotypes, powerfully reminding us that neuroscience can be dangerous when mishandled.”
[Barres BA (2010) Neuro Nonsense. PLoS Biol 8(12): e1001005. doi:10.1371/journal.pbio.1001005 – http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1001005]
- Articolo scientifico del 2011:
“In addition to interviewing scientists about how they do their work,
Jordan-Young analyzed over 300 research studies examining the proposed link between prenatal hormone exposures and human sexuality or gender, published from the late 1960s through 2008. […] In the end, she concludes that the available evidence does not support the theory—which, as she herself points out, directly informs several existing and highly continuous debates about whether men and women “naturally” think differently because their
brains are hormonally organized as masculine or feminine (including debates about the lack of women in science and engineering disciplines).”
[Bridget K. Gorman. Brain Storm: The Flaws in the Science of Sex Differences by Rebecca M. Jordan-Young The Mirage of a Space between Nature and Nurture by Evelyn Fox Keller. American Journal of Sociology, Vol. 116, No. 6 (May 2011), pp. 2019-2022. – http://www.rebeccajordan-young.com/uploads/7/9/8/4/7984974/ajs_review.pdf]
- Articolo scientifico del 2012:
“Evidence has long suggested that ‘hardwiring’ is a poor metaphor for brain development. But the metaphor may be an apt one for the dominant paradigm for researching sex differences, which pushes most neuroscience studies of sex/gender inexorably towards the ‘discovery’ of sex/gender differences, and makes contemporary gender structures appear natural and inevitable. The argument we forward in this paper is twofold. In the first part of the paper, we address the dominant ‘hardwiring’ paradigm of sex/gender research in contemporary neuroscience, which is built on broad consensus that there are important ‘original’ sex differences in brain structure and function, organized by sex-differentiating prenatal hormone exposures. We explain why this consensus is both unscientific and unethical. In the second part of the paper, we sketch an alternative research program focused not on the origins of sex/gender differences but on variability and plasticity of brain/behavior. We argue that interventional experiments based on this approach will address more tractable questions, and lead to much more satisfactory results than the brain organization paradigm can provide.”
[Jordan-Young, R. & Rumiati, R.I. (2012). Hardwired for sexism? Approaches to sex/gender in neuroscience. Neuroethics, 5(3), 305-315. – http://www.rebeccajordan-young.com/uploads/7/9/8/4/7984974/hardwired_for_sexism.pdf]
- Sviluppo cerebrale – Articolo del 2013 sulla prestigiosa rivista Cell (più precisamente Cell – Trends in Cognitive Sciences):
“Perché la comprensione popolare delle differenze di sesso femminile-maschile è ancora basata su modelli rigidi di sviluppo, anche se le scienze dello sviluppo contemporanee sottolineano la plasticità? È perché la scienza delle differenze tra i sessi funziona ancora sugli stessi modelli rigidi?”
[Fine C, Jordan-Young R, Kaiser A, Rippon G. Plasticity, plasticity, plasticity…and the rigid problem of sex. Trends Cogn Sci. 2013 Nov;17(11):550-1.]
- Articolo scientifico su Nature:
“First, human sex differences are elevated almost to the point ofcreating different species, yet virtually all differences in brain structure, and most differences in behaviour, are characterized by small average differences and a great deal of male–female overlap at the individual level. Second, data on structural and functional differencesin the brain are routinely framed as if they must precede all sex differences in behaviour. Finally, the focus on hormone levels to the virtual exclusion of the systems that interpret them (and the mutual regulatory interactions between receptor and secretion systems) is especially lamentable, given the book’s clinicalemphasis on hormone therapies. Misrepresentations of scientific detailsare legion. Readers who studied biology in high school may puzzle over the invocations of the male brain with its single “dose of X chromosome (there are two Xs in a girl)”: is the author suggesting that X-chromosome dosage compensation is absent from female brains? Is it an improvement to dispel the myth thattestosterone is a “male hormone” only to call it the “sex and aggression hormone”? (If eachhormone needs a sound bite, “confidence andsense of well-being hormone” might better fitthe data.) Ironically, at the intracellular level, much of the differentiation of the “ testosterone-formed male brain” is accomplished by oestrogens. Fostering such misleading metaphorsmay prevent broader understanding.
The emphasis on myth-busting turns into avehicle for dressing the myth upin new clothes — such as Simon Baron-Cohen’s recent hypothesis that the ‘male brain’ is hard-wired for ‘systematizing’, and the ‘female brain’ is hard-wired for ‘empathizing’ — there is no shortage of pseudo-scientific ways of saying‘thinkers’ and ‘feelers’. The problem with such explanations of sex differences is not that they are overly biological, but that they are fundamentally non-biological andexplain nothing.
The melodrama obscures how biology matters; neither hormones nor brains are pink or blue. Our attempts to understand the biology ofhuman behaviour cannot move forward untilwe try to explain things as they are, not as wewould like them to be.”
[Young, R.M. and Balaban, E. Psychoneuroindoctrinology. Review of The Female Brain by Louanne Brizendine. Nature 443 (12): 634, 2006. – http://www.rebeccajordan-young.com/uploads/7/9/8/4/7984974/youngbalaban_psychoneuroendoctrinology.pdf%5D
- Articolo scientifico del 2011:
“Brain organization theory suggests that steroid hormones during fetal development permanently organize the brain for gender, including patterns of sexuality, cognition, temperament, and interests that differ by sex. This widely-accepted theory has important implications for health, ranging from medical management of infants with intersex conditions to suggested etiologies for sex differences in autism, depression, and other mental health problems. Studies of genetic females with congenital adrenal hyperplasia (CAH), in which high prenatal androgens have been linked to both atypical genitals and “masculine” patterns of gender and sexuality, are particularly important. Based on a comprehensive review of research on CAH, this article demonstrates that such studies have neglected four broad categories of variables that plausibly affect psychosexual development: (1) physiological effects of CAH, including complex disruption of steroid hormones from early development onwards; (2) intensive medical intervention and surveillance, which many women with CAH describe as traumatic; (3) direct effects of genital morphology on sexuality (versus indirect effects that “masculine” genitals may have on gender socialization); and (4) expectations of masculinization that likely affect both the development and evaluation of gender and sexuality in CAH. Complex and iterative interactions among postnatal biological variables, medical interventions, and social context provide a more plausible explanation for atypicalities in psychology and behavior that have been reported for genetic females with CAH than the conventional explanation that early androgens have “masculinized” their brains.”
[Jordan-Young RM. Hormones, context, and “brain gender”: a review of evidence from congenital adrenal hyperplasia. Soc Sci Med. 2012 Jun;74(11):1738-44. doi: 10.1016/j.socscimed.2011.08.026. Epub 2011 Sep 17. – http://www.rebeccajordan-young.com/uploads/7/9/8/4/7984974/asds_and_gendered_embodiment_final.pdf]
- Articolo scientifico del 2013:
“The neuroscientific investigation of sex differences has an unsavoury past, in which scientific claims reinforced and legitimated gender roles in ways that were not scientifically justified. Feminist critics have recently argued that the current use of functional neuroimaging technology in sex differences research largely follows that tradition. These charges of ‘neurosexism’ have been countered with arguments that the research being done is informative and valuable and that an over-emphasis on the perils, rather than the promise, of such research threatens to hinder scientific progress. To investigate the validity of these contrasting concerns, recent functional magnetic resonance imaging (fMRI) investigations of sex differences and citation practices were systematically examined. In line with the notion of neurosexism, the research was found to support the influence of false-positive claims of sex differences in the brain, to enable the proliferation of untested, stereotype-consistent functional interpretations, and to pay insufficient attention to the potential plasticity of sex differences in both brain and mind. This, it is argued, creates a literature biased toward the presentation of sex differences in the brain as extensive, functionally significant, and fixed—and therefore implicitly supportive of a gender essentialist perspective. It is suggested that taking feminist criticisms into account would bring about substantial improvement in the quality of the science, as well as a reduction in socially harmful consequences.”
[C. Fine. (2013). Is there neurosexism in functional neuroimaging investigations of sex differences? Neuroethics, 6(2), 369–409. – http://link.springer.com/article/10.1007%2Fs12152-012-9169-1#page-1]
- Studio del 2008 che spiega che gli ormoni non vanno a creare “cervelli distinti” per i due sessi:
“This study explores the extent to which the term “sex hormone” is used in science textbooks, and whether the use of the term “sex hormone” is associated with pre-empirical concepts of sex dualism, in particular the misconceptions that these so-called “sex hormones” are sex specific and restricted to sex-related physiological functioning. We found that: (1) all the texts employed the term “sex hormone”; (2) in all texts estrogen is characterized as restricted to females and testosterone is characterized as restricted to males; and (3) in all texts testosterone and estrogen are discussed as exclusively involved in sex-related physiological roles. We conclude that (1) contemporary science textbooks preserve sex-dualistic models of steroid hormones (one sex, one “sex hormone”) that were rejected by medical science in the early 20th century and (2) use of the term “sex hormone” is associated with misconceptions regarding the presence and functions of steroid hormones in male and female bodies.”
“In the 1930’s it became clear that “sex hormones” were not sex specific and did not have sexually restricted physiological roles. By 1938 it was well recognized that estrogens were “not merely sex hormones, but…hormones also possessing manifold important eVects on non-sexual organs.” (Fausto-Sterling 2000). The one hormone per sex model was clearly challenged by the idea that each sex had “male” and “female” hormones. Consequently, the term “sex hormone” lost much of its meaning, and debate ensued over what names to give these substances. In the end, however, the idea of sex-specificity was implicitly retained when ‘androgens’ (to build a man) and ‘estrogens’ (to cause estrus) were chosen as the new terms (Fausto-Sterling 2000, p. 188). Oudshoorn (1994, p. 26) has argued that evidence of ‘cross-sex’ hormones “…led to a drastic break with the dualistic cultural notion of masculinity and femininity that had existed for centuries.” Yet, in the nearly 70 years since the establishment that the “sex hormones” are neither sex-specific nor restricted to sex-related organs or functions, the term “sex hormones” has survived in endocrinology as well as in popular culture, science textbooks, and the popular press. The persistence of sex-specific terminology (‘sex hormones,’ ‘estrogens,’ and ‘androgens’) raises questions about just how completely this dualistic notion has been uprooted by the force of evidence. Interpretive problems remain (e.g., How does an ‘estrus-causing hormone’ function in a male body? How does a ‘male development hormone’ function in female bodies?). Fausto-Sterling (2000) in particular has argued that the terminology of “sex hormones” is an obstacle to accurate scientific understanding. Indeed, the history of endocrinology exposes episodes of considerable anxiety and non-parsimonious reasoning in scientists when biological results did not match cultural notions of sex and gender (Oudshoorn 1994; Fausto-Sterling 2000; Young 2000).”
[Ross H. Nehm, Rebecca Young. (2008). “Sex Hormones” in Secondary School Biology Textbooks. Science & Education, 17(10):1175-1190. – http://www.researchgate.net/publication/227322593_Sex_Hormones_in_Secondary_School_Biology_Textbooks]
- Studio del 2014:
Feminist neuroscientists have uncovered inconsistent findings concerning sex differences and elaborated similarities between or variations within the gender groups, not only on the level of behavior and performance but also concerning their apparently biological sources, i.e., the brain networks and their functions (Frost et al., 1999; Blanch et al., 2004; Ulshöfer, 2008; Wallentin, 2009; Jordan-Young, 2010; Bluhm et al., 2012; Jordan-Young and Rumiati, 2012; Kuria, 2012; Roy, 2012; Vidal, 2012; Dussauge, 2014; Kaiser, 2014; Sommer et al., 2004, 2008).
Differentiated analyses systematically investigated methodical influences on neuroscientific knowledge production in sex/gender research. Scholars such as Bishop and Wahlstein (1997), Fine (2013), Kaiser et al. (2009) and Schmitz (2010) have uncovered variations in data selection, statistical analyses, and computer tomographic calculations that contradict generalizations being made throughout various studies. The fact that these meta-studies have been included in scholarly neuroscience journals attests an increasing sensitization towards critical reflections on methods within brain analyses. Nonetheless, even now, studies that establish differences between sex/gender are published more often than studies that do not find differences (Kaiser, 2012; Fine, 2013). Although the reasons of such ‘publication biases’ may be manifold (e.g., caused by the emphasis for getting research funding within the sciences or due to catching the interests of the public target groups in popular press), they still manifest notions of a binary gender order and foster the persistence of seemingly biologically determined gendered significations.
Today, brain plasticity studies in humans address the development of different language networks and brain functionalities in line with individual language biographies (Bloch et al., 2009), changes in spatial and motoric areas correlated to long-term navigation experience (Maguire et al., 2000) or structural changes in the corpus callosum (e.g., Gaser and Schlaug, 2003) and motoric brain networks following shorter periods of learning juggling (Draganski et al., 2004). Plasticity concepts have therefore led to a redefinition of cause and effect in ‘neuro-argumentations’, as the biological system of the brain is extremely open and able to adapt diverse influences over the course of a lifetime. From this constructivist perspective, the brain cannot be characterized as solely physical matter and as the only essence of behavior. It must be analyzed in regards to its continuous entanglements with the outer world. Cultural and social experiences influence behavior by forming and shaping the biology of the brain. Recent studies on how the experience with virtual games diminishes sex/gender differences are indicative of the necessity of these constructions of competences (Feng et al., 2007), for which brain studies have also argued (Jordan-Young, 2010). During the last decade, neurofeminist scholars more and more used the perspective of plasticity to analyze the material-discursive entanglements of brains and their environments (Schmitz, 2010; Jordan-Young and Rumiati, 2012; Vidal, 2012). […]
Accordingly, brain images are snapshots of a certain moment of physical materiality, which is always connected to individual biographies. Results of brain scans can thus not provide information on the processes that led to these developments, neither from nature nor from culture. Despite this obvious critique, the “snapshot approach” is mostly used in place of plasticity considerations for the interpretation of results (Schmitz, 2010), and it persists even in recent sex/gender-related brain imaging studies, as Fine (2013) has analyzed.
The brain plasticity concept is important for deconstructing unilinear statements about a supposedly biological determination of behavior, attitudes, etc. In narrating plasticity stories, neurofeminist scholars mainly stress a return of genealogies of cause and effect, arguing that gendered social experiences and power relations impact the forming of the gendered brain’s structure and function more than vice versa (e.g., Vidal, 2012).
[Schmitz S, Höppner G. Neurofeminism and feminist neurosciences: a critical review of contemporary brain research. Front Hum Neurosci. 2014 Jul 25;8:546.]
- Studio del 2012:
- Studio del 2014
Similarly in neuroscience, the phenomenon of brain mosaicism has been recognized for decades (Witelson, 1991; Cahill, 2006; McCarthy and Arnold, 2011, see also Joel, 2011). That is, an individual does not have a uniformly “female” or “male” brain, but the “male” form (as statistically defined) in some areas and the “female” form in others, and in ways that differ across individuals. (Nor is this necessarily static, with animal research indicating that even brief experiences such as stress exposure can change brain characteristics from the “female” to the “male” form, and vice versa; see Joel, 2011). […] Mosaicism of gendered behavior and brains is a critically important point, because it conflicts with the more (although not absolutely) categorical nature of biological sex, in which female/male differences in sex chromosomes, gonads and genitals are roughly dimorphic and highly interrelated, such that individuals mostly have a unitary “male” or “female” phenotype.
[…] At the group level, women’s expression of “masculine” personality traits (such as assertiveness) appears to be responsive to cultural shifts in social status and role (Twenge, 1997, 2001), while in the shorter term, gendered behavior is flexibly responsive to social context and experience. For example, a meta-analysis conducted by Ickes et al. (2000) found that a moderate female advantage in empathic accuracy was only observed if participants were also asked to make self-ratings of their accuracy (hypothesized to preferentially enhance women’s motivation to perform well). Another well-known example of social contextual effects on gendered behavior is the “stereotype threat” phenomenon whereby, for instance, female mathematical performance is diminished when tests are presented in a way that makes salient the stereotype that females are poor at mathematics (Nguyen and Ryan, 2008; Walton and Spencer, 2009), although we acknowledge the more sceptical conclusion regarding the size, robustness, and generality of the stereotype threat effect from the meta-analysis by Stoet and Geary, 2012. As a third example, the average male advantage in mental rotation is diminished by altering how the task is framed (e.g., Moè, 2009). Moreover, the beneficial effects of training, including video-gaming, points to the contribution of gendered experience to this skill (Feng et al., 2007). (For numerous additional examples of stereotype threat effects on sex/gender differences, see Fine, 2010a). […] From this brief discussion it should therefore not be surprising that, in contrast with the near complete consistency of genetic, gonadal and genital differences between the sexes, female/male differences in behavior are variable across time, place, social or ethnic group, and social situation. […] For example, as reviewed in Hyde (2014), female/male differences in mathematics in the USA have not only decreased over time but also vary or even reverse according to ethnic group. A review of differences in math achievement in 69 nations by Else-Quest et al. (2010) revealed that gender differences were not only very small, but highly variable, with effect sizes ranging from −0.42 (a moderate difference favoring females) to 0.40 (a moderate difference favoring males); socio-cultural factors such as women’s parliamentary representation, equity in school enrolment, and women’s share of research jobs were significant predictors of gender gaps in math achievement. As with cognitive skills, female/male differences in personality (e.g., neuroticism/anxiety) or well-being (e.g., self-esteem) that are seen in one country or ethnic group are not necessarily observed in others (Costa et al., 2001, reviewed in Hyde, 2014). […] As indicated above, there is considerable evidence that average female/male differences can be modified, neutralized, or even reversed by specific context, for example the manipulation of the salience of such differences, or by chronic structural factors in the environment, such as national wealth or gender equity (reviewed in Miller and Halpern, 2013; Hyde, 2014). Clearly, this will be reflected in the neural substrates of such behavior, which therefore cannot be universal or fixed (see Fine, 2013b). This type of finding is in keeping with the rejection of early models of the relationship between brain and behavior in the study of sex/gender. These were based on a fairly simple, almost unidirectional concept of “hard-wiring”, in which brain characteristics were conceived as being predetermined by the organizational effects of genetically-programmed prenatal hormonal influences (Phoenix et al., 1959). Here, each individual is endowed with a “female” or “male” brain that gives rise to feminine and masculine behavior, respectively; a neural substrate that social factors merely influence. This assumption of distinctive female vs. male brain circuitry, largely fixed by a sexually-differentiated genetic blueprint, is now clearly challenged by changed models of neurodevelopment and wide-spread consensus of on-going interactive and reciprocal influences of biology and environment in brain structure and function (Li, 2003; Lickliter and Honeycutt, 2003; van Anders and Watson, 2006; Hausmann et al., 2009; McCarthy and Arnold, 2011; Miller and Halpern, 2013). As NI research itself has been instrumental in demonstrating, such interactions leave neural traces. A recent review by May (2011) summarizes the evidence that new events, environmental changes and skill learning can alter brain function and the underlying neuroanatomic circuitry throughout our lives. […] NI studies have demonstrated how neuronal plasticity has been related to sex/gender. Wraga et al. (2006), using a direct comparison of task-related positive and negative stereotype priming, showed that the neural correlates of performance of the same task reflected this priming, demonstrating short-term plasticity of neural function. Longer-term functional and structural plasticity was indicated in another within-sex study investigating the neural effects in adolescent girls of 3 months of training with the visuo-spatial problem solving computer game Tetris (Haier et al., 2009). […] As will by now be clear from the discussion of the key principles of sex/gender scholarship, gender essentialist assumptions are inappropriate, and the experimental context complex and contingent. Any one sample will consist of individuals with an intricate mosaic of gendered attributes, the distributions for many of which will be largely overlapping and may not differ at the group level in that particular sample. Similarly, the individuals in the sample will not have “female” or “male” brains as such, but a mosaic of “feminine” and “masculine” characteristics. Whatever female/male behavioral and therefore brain differences are observed in that particular sample are contingent on both chronic and short-term factors such as social group (such as social class, ethnicity), place, historical period, and social context and therefore cannot be assumed a priori to be generalizable to other populations or even situations (such as the same task performed in a different social context). Each individual’s behavioral and neural phenotype at the moment of experimentation is the dynamic product of a complex developmental process involving reciprocally influential interactions between genes, brain, social experience, and cultural context. Simpler, implicitly essentialist models (see lower, shaded portion of Figure 1) will need to be replaced by more complex multivariate models which acknowledge the interactive contribution of many additional sociocultural factors (see upper portion of Figure 1).
[Rippon G, Jordan-Young R, Kaiser A, Fine C. Recommendations for sex/gender neuroimaging research: key principles and implications for research design, analysis, and interpretation. Front Hum Neurosci. 2014 Aug 28;8:650.]
- Studio del 2015 su PNAS:
“Documented sex/gender differences in the brain are often taken as support of a sexually dimorphic view of human brains (“female brain” or “male brain”). However, such a distinction would be possible only if sex/gender differences in brain features were highly dimorphic (i.e., little overlap between the forms of these features in males and females) and internally consistent (i.e., a brain has only “male” or only “female” features). Here, analysis of MRIs of more than 1,400 human brains from four datasets reveals extensive overlap between the distributions of females and males for all gray matter, white matter, and connections assessed. Moreover, analyses of internal consistency reveal that brains with features that are consistently at one end of the “maleness-femaleness” continuum are rare. Rather, most brains are comprised of unique “mosaics” of features, some more common in females compared with males, some more common in males compared with females, and some common in both females and males. Our findings are robust across sample, age, type of MRI, and method of analysis. These findings are corroborated by a similar analysis of personality traits, attitudes, interests, and behaviors of more than 5,500 individuals, which reveals that internal consistency is extremely rare. Our study demonstrates that, although there are sex/gender differences in the brain, human brains do not belong to one of two distinct categories: male brain/female brain.”
The low degree of internal consistency observed here in the human brain agrees well with studies demonstrating that humans often possess both “masculine” and “feminine” psychological characteristics (that is, personality traits, attitudes, interests, and behaviors that show sex/gender differences). Early attempts in the first half of the 20th century to measure masculinity-femininity using specially constructed scales have already revealed low or absent correlations between subscales measuring different characteristics of gender (17). Similar findings have led Janet Spence (18) to conclude that humans possess an array of masculine and feminine traits that cannot be captured using a uni-dimensional (masculinity-femininity) or a bidimensional (masculinity × femininity) model.
In accordance with the brain data, our analyses of gender-related data revealed extensive overlap between females and males in personality traits, attitudes, interests, and behaviors. Moreover, we found that substantial variability of gender characteristics is highly prevalent, whereas internal consistency is extremely rare, even for highly gender-stereotyped activities (Carothers and Reis’ data). These findings are in line with previous reports that sex/gender differences in abilities and qualities are mostly nonexistent or small, that there is extensive overlap between the distribution of males and females also in behaviors, interests, occupation preferences, and attitudes that show larger sex/gender differences (24, 25), and that there are no or only weak correlations between gender characteristics (18, 20, 21). Thus, most humans possess a mosaic of personality traits, attitudes, interests, and behaviors, some more common in males compared with females, others more common in females compared with males, and still others common in both females and males.
[Joel D, Berman Z, Tavor I, Wexler N, Gaber O, Stein Y, Shefi N, Pool J, Urchs S, Margulies DS, Liem F, Hänggi J, Jäncke L, Assaf Y. Sex beyond the genitalia: The human brain mosaic. Proc Natl Acad Sci U S A. 2015 Dec 15;112(50):15468-73.]
- Questo studio ha ricevuto delle critiche, ma gli autori hanno risposto a tali obiezioni, smontandole completamente:
“The rational for our method of analysis was derived from animal studies demonstrating that in contrast to sex effects on genital organs, sex effects on brain features may be opposite under different environmental conditions. That is, what is typical in one sex category (e.g., females) under some conditions may be typical in the other sex category under other conditions (reviewed in refs. 2 and 3). As a result, brains are expected to be composed of both features more common in males compared with females and features more common in females compared with males, a situation that rarely occurs in genitalia. When it does occur, the genitalia are classified as “intersex” and not as “male” or “female” (5). […] the fact that the large majority of brains consist of unique mosaics of “male-end,” “female-end,” and intermediate (i.e., common in both females and males) features precludes any attempt to predict an individual’s unique brain mosaic on the basis of sex category (2–4).
Del Giudice et al. (6) provide an elegant validation of our method of analysis, by demonstrating that internal consistency is higher than substantial variability when distinct populations (facial morphology of different primate species) are assessed. Thus, with a cutoff of 33%, internal consistency was found in 1.1–5.1% of profiles (depending on the pair of primates assessed) and substantial variability in 0% (6), compared with 0–8.2% internally consistent brains and 23–53% substantially variable brains [depending on the dataset (1)]. This comparison also reveals a degree of “mosaicism” in brains that is much higher than that found in primate species and provides further support to our conclusion that human brains do not belong to two distinct populations.
Using simulations in which they systematically varied the size of sex/gender differences and of correlations between variables, Del Giudice et al. (6) further demonstrated that our method of analysis returns more substantially variable profiles than internally consistent profiles, unless correlations and/or sex/gender differences become extremely large. These simulations corroborate our simulations (1), in which we systematically varied the mean random noise added to an otherwise internally consistent “brain.” Although the correlations between variables change as random noise is added, the multivariate distribution of variables created this way differs from that of the variables created by Del Giudice et al. (6). Indeed, for similarly sized correlations (0.7–0.8) and sex differences (0.70 < d ≤ 0.84) our simulation revealed more internally consistent “brains” than substantially variable “brains” (1), whereas Del Giudice et al. (6) found the reverse (less internally consistent “brains” than substantially variable “brains”). Together, these simulations demonstrate that our method of analysis can differentiate between an internally consistent system with some degree of random noise (our simulated data) and a system in which there are similar correlations between variables but with no underlying internal consistency [the simulated data of Del Giudice et al. (6)].
Del Giudice et al. (6), Rosenblatt (7), and Chekroud et al. (8) achieved better accuracy in predicting an individual’s sex category on the basis of brain form, using supervised learning over all brain measures to find the space in which brains of females and brains of males are most separated. […] Although the different supervised learning methods achieve better accuracy in predicting sex category than the simple method described above, they have the same conceptual problem, namely, it is unclear what the biological meaning of the new space is and in what sense brains that seem close in this space are more similar than brains that seem distant. Moreover, it is unclear whether the brain variability that is represented in the new space is related to sex or rather to physiological, psychological, or social variables that correlate with sex (e.g., weight, socioeconomic status, or type of education) or to a chance difference between the males and females in the sample (2, 4). One way to answer this question is by checking whether a model created to predict sex category in one dataset can accurately predict sex category in another dataset. Using SVM, we found that accuracy may drop dramatically (sometimes to less than 50%) when a model created using a dataset from one geographical region (Tel-Aviv, Beijing, or Cambridge) was tested on the other datasets.”
[Joel D, Persico A, Hänggi J, Pool J, Berman Z. Reply to Del Giudice et al., Chekroud et al., and Rosenblatt: Do brains of females and males belong to two distinct populations? Proc Natl Acad Sci U S A. 2016 Apr 5;113(14):E1969-70.]
- Ulteriore risposta:
“Glezerman overlooks, however, the fact that such differences may be different and even opposite under different environmental conditions. That is, what is typical under some conditions in a brain composed of cells with an XX chromosomal complement residing in a body with low levels of testosterone, may be typical under other conditions in a brain composed of cells with an XY chromosomal complement residing in a body with high levels of testosterone. Such “reversals” of sex effects have also been reported when the manipulation of environmental conditions was done in utero (by manipulating the dam) and the offspring were tested in adulthood (reviewed in refs. 2 and 3). These observations led to the hypothesis that brains are composed of a “mosaic” of “male” and “female” features rather than of only “male” features or only “female” features, as expected of a “male brain” and a “female brain,” respectively (2, 3).”
[Joel D, Hänggi J, Pool J. Reply to Glezerman: Why differences between brains of females and brains of males do not “add up” to create two types of brains. Proc Natl Acad Sci U S A. 2016 Apr 5;113(14):E1972.]
- Studio del 2016 della Royal Society, chiamato appunto “Al di là delle differenze tra i sessi” (“Beyond sex differences”):
“In the study of variation in brain structure and function that might relate to sex and gender, language matters because it frames our research questions and methods. In this article, we offer an approach to thinking about variation in brain structure and function that pulls us outside the sex differences formulation. We argue that the existence of differences between the brains of males and females does not unravel the relations between sex and the brain nor is it sufficient to characterize a population of brains. Such characterization is necessary for studying sex effects on the brain as well as for studying brain structure and function in general. Animal studies show that sex interacts with environmental, developmental and genetic factors to affect the brain. Studies of humans further suggest that human brains are better described as belonging to a single heterogeneous population rather than two distinct populations. We discuss the implications of these observations for studies of brain and behaviour in humans and in laboratory animals. We believe that studying sex effects in context and developing or adopting analytical methods that take into account the heterogeneity of the brain are crucial for the advancement of human health and well-being.”
[Joel D., Fausto-Sterling A. Beyond sex differences: new approaches for thinking about variation in brain structure and function. Philos Trans R Soc Lond B Biol Sci. 2016 Feb 19;371(1688):20150451.]