and Scientific Criticism
In the recent Cerebrum article, “Equal ≠ The Same: Sex Differences in the Human Brain,” author Larry Cahill offers
his perspective on the nature of sex differences in brain and behavior, and
what he considers to be a “counter-reaction” to such research by “anti-sex
difference” investigators operating from the “deeply ingrained, implicit, false
assumption that if men and women are equal, then men and women must be the
We welcome this opportunity to correct some
of the misapprehensions and mischaracterizations in this account, and present a
more nuanced view of the relations among sex, brain, and gender.
Like Cahill and many others, we welcome more
active research on females in basic animal neuroscience. We strongly believe
that this is necessary to ensure that basic research is relevant to all humans.
We are concerned, though, that
one mistake, treating males as the norm, will be replaced with another;
namely, treating males and females as two distinct entities.
Relatedly, we all believe, like Cahill, that
sex matters; that is, that genetic and gonadal sex can influence brain
development and function at every level, that useful information may arise from
investigating such processes, and that this may be especially critical in
understanding pathological development. Indeed, numerous explicit statements to
this effect can be found in our work.
Moreover, Joel’s lab empirically investigates
and Rippon, Jordan-Young, Kaiser and Fine
recently made extensive recommendations in Frontiers in Human Neuroscience as to
best practice methods, analysis, and interpretation in sex/gender neuroscience.
We were therefore surprised to find ourselves characterized as “anti-sex
difference” researchers. We are neither “for” nor “against” sex differences (or
sex similarities, for that matter);
focusing only on similarities or differences is
misleading. We need to develop a new framework for thinking of the relation
between sex, brain, and gender that better fits current knowledge, and that
takes into account distributions, changes, overlap, variance, and most of all,
Thus, a critical point that is absent in
Cahill’s article is that the effects of sex on the brain can be opposite under
different conditions. T
hat is, what is typical in one sex under some
conditions may be typical in the other sex under other conditions. Moreover,
the specific interactions between sex and
other factors (environmental, developmental, genetic) are different for
different brain regions, and are not necessarily stable over time. As a result,
the brains of women and men each comprise a unique, ever-changing ‘mosaic’ of
features, some of which may be more typical in males and some of which may be
more typical in females.8 Thus brains, in contrast to genitals, do
not come in distinct, fixed male or female forms.
In contrast, the metaphor Cahill uses reflects
a common assumption
that the average differences between women
and men in the brain as well as in traits, attitudes, interests, roles, skills,
cognitive, and emotional abilities and personality characteristics add up to
create two distinct systems:
“claiming that there are no reliable sex differences
on the basis of analyzing isolated functions is rather like concluding, upon
careful examination of the glass, tires, pistons, brakes, and so forth, that
there are few meaningful differences between a Volvo and a Corvette.”
But sex differences in brain and gender are
very different from differences between car brands and between female and male
genitals. A car with Corvette tires will almost certainly also have Corvette
pistons, brakes, and glass (but not Volvo pistons or brakes), just like a
person with a womb will almost certainly also have a vagina, clitoris, and
labia (but no penis or scrotum). By contrast, knowing that a person has a
‘masculine’ mental rotation score, say, tells you very little about whether
they will be masculine or feminine in other aspects of gender, because each
person has a unique array of gender characteristics.
Would we classify cars
Corvettes if each car had a unique combination of glass, tires, pistons,
brakes, and so on from both the Volvo and the Corvette factories?
Moreover, would we classify glass, tires,
pistons, brakes, etc. as being of Volvo or Corvette origin if engines of Volvos
changed form to become powerfully Corvette-like under some conditions, and
trunks of Corvettes changed to become more spacious, depending on the specific
social context in which the car found itself? Or if, in some social contexts
and countries, the pistons of Volvos differed quite significantly from those of
Corvettes, but in other circumstances or countries they were the same? This
clearly never happens with car parts or genitals, but has been repeatedly
demonstrated for gendered behaviors
and brain structure.
Carothers and Reis’s taxonomic analysis of
gender, which Cahill cites, demonstrated exactly this distinction.
Thus, they did indeed find categorical
differences between the sexes for highly sex-stereotyped activities (like
playing golf and wearing make-up). Yet, these were specifically selected to
demonstrate the validity of their taxonomic methods.
To be precise, heterosexual, midwestern American undergraduates were asked to
identify things that women versus men “typically enjoyed during their free time.”
Validity testing in a second similar group winnowed the list of 129 items down
to 28. In the larger sample—again heterosexual, Midwestern U.S. college
students—10 of these 28 showed large sex differences (d>1), confirming that taxometric
procedures could effectively detect
taxa in gender-related constructs. What Cahill fails to mention,
however, is that for virtually all of the other
gendered characteristics analyzed (covering such domains as sexual attitudes
and behaviors, care orientation, science inclination, and Big Five personality
traits), the researchers drew precisely the opposite conclusion. “[A]lthough
there are average differences between men and women, these differences do not
support the idea that ‘men are like this, women are like that.’ ” Rather:
differences are better understood as individual differences that vary in
magnitude from one attribute to another rather than as a suite of common differences
that follow from a person’s sex.”
So human brains and behaviors
do not come in two distinct forms? What about the relations between the two? Can
we relate behavioral differences to structural differences, as
did in the PNAS paper Cahill cites
This study reported average sex differences in
brain connectivity and speculated that these connectivity differences were
differences found in another study on the same
participants in several behavioral measures (e.g., executive control, memory,
reasoning, spatial processing, sensorimotor skills, and social cognition). Yet
the researchers did not use their data to directly test their hypothesis that
sex differences in brain connectivity were related to behavioral sex
differences. An alternative possibility is that the observed connectivity
differences have no functional implications, perhaps, for example, serving to
offset average brain size differences between the sexes.
Indeed, this alternative hypothesis arises
directly from de Vries’ claim, cited by Cahill, that sex differences in the
brain sometimes serve to compensate for other differences (rather than to
create further differences), thus making the two sexes more similar.
It matters that women and men are not like
Volvos and Corvettes. It matters scientifically, with respect to research
models, methods, analysis, and interpretation. The elucidation of these issues
has been a primary goal of our work: for example, in relation to functional
prenatal hormonal influences on the brain,
and sex differences in psychopathology.
But it is also a matter of importance to the
general public that women and men are not like Volvos and Corvettes. There is
growing evidence that thinking about the brains and behavior of males and
females in this inappropriately categorical way has psychosocial effects that
serve to sustain the gender status quo
for review see 21
also 22 for an analysis of media and social media commentary arising from
Ingalhalikar et al.'s PNAS article and press release
. People look to Volvos for a safe car for the
family, and to Corvettes for status and power. Categorical thinking about
gender reinforces the idea that similar divisions in social roles for women and
men are appropriate, fixed, natural, and inevitable. We are therefore grateful
for this opportunity to indicate just how misleading this is as a metaphor.
We appreciate fears on the part of
neuroscientists that blanket antipathy towards the investigation of sex
influences on the brain could stifle research opportunities. As we hope is now
clear, we are all for investigating sex, gender, and their interlacements.
However, the research models neuroscientists (and others) use should be
appropriate to the phenomena in question.
- Cordelia Fine: Melbourne School of
Psychological Sciences, Melbourne Business School & Centre for Ethical
Leadership, University of Melbourne
- Daphna Joel: School of Psychological
Sciences & Sagol School of Neuroscience, Tel-Aviv University
- Rebecca Jordan-Young: Department of
Women’s, Gender & Sexuality Studies, Barnard College, Columbia University
in the City of New York
- Anelis Kaiser: Department
of Social Psychology and Social Neuroscience, Institute of Psychology,
University of Bern
- Gina Rippon: Aston Brain Centre,
School of Life & Health Sciences (Psychology), Aston University
The Author Responds
he article is the response I had been waiting for, from the group I was expecting it from. I am glad to know they value my opinion enough to have read my article. Nothing in their response undermines anything I wrote, so I stand by my article completely. I encourage the reader to read and critically evaluate both articles, and form their own opinions.
In my view the
most important point for the reader to be aware of regarding the sex difference
issue is that, since the time of my Cerebrum
article, the National Institutes of Health has—for the first time—announced
that all research they support will soon be required to carefully address
potential sex differences.1 This is a remarkable development for
research and medicine, and one that I, and everyone who appreciates the
importance of sex influences, have been working toward for years. I hope Fine
et al appreciate this development as well, especially as women, who will be the
ones to disproportionately benefit from it.
— Larry Cahill, Ph.D.
1. Cahill, L. Equal ≠ the same: Sex differences in the human brain. Cerebrum,
2. Jordan-Young, R., Brain storm: The flaws in the science of sex
differences2010, Cambridge, MA: Harvard University Press.
3. Fine, C., Delusions of gender: How our minds, society, and neurosexism create
difference2010, New York: WW Norton.
4. Fine, C., Is there neurosexism in functional neuroimaging investigations of sex
differences? Neuroethics, 2013. 6(2):
5. Joel, D. and R. Yankelevitch‐Yahav, Reconceptualizing sex, brain and
psychopathology: Interaction, interaction, interaction. British journal of
6. Flaisher-Grinberg, S., et al., Ovarian hormones modulate
‘compulsive’lever-pressing in female rats. Hormones and Behavior, 2009. 55(2): p. 356-365.
7. Rippon, G., et al., Recommendations for sex/gender neuroimaging
research: key principles and implications for research design, analysis, and
interpretation. Frontiers in Human Neuroscience, 2014. 8: p. 650.
8. Blackless, M., et al., How sexually dimorphic are we? Review and
synthesis. American Journal of Human Biology, 2000. 12(2): p. 151-166.
9. Haslam, N., L. Rothschild, and D.
Ernst, Essentialist beliefs about social
categories. British Journal of Social Psychology, 2000. 39: p. 113-127.
10. Hyde, J.S., Gender Similarities and Differences. Annual Review of Psychology,
2014. 65(1): p. 373-398.
11. Joel, D., Male or female? Brains are intersex. Frontiers in Integrative
Neuroscience, 2011. 5(Article 57).
12. Carothers, B.J. and H.T. Reis, Men and women are from Earth: Examining the
latent structure of gender. Journal of Personality and Social Psychology,
2013. 104(2): p. 385-407.
13. Reis, H.T. and B.J. Carothers, Black and White or Shades of Gray: Are
Gender Differences Categorical or Dimensional? Current Directions in
Psychological Science, 2014. 23(1):
14. Ingalhalikar, M., et al., Sex differences in the structural connectome
of the human brain. Proceedings of the National Academy of Sciences, 2014. 111(2): p. 823-828.
15. Jäncke, L., et al., Brain size, sex, and the aging brain.
Human Brain Mapping, 2014.
16. de Vries, G.J. and P. Sodersten, Sex differences in the brain: The relation
between structure and function. Hormones and Behavior, 2009. 55(5): p. 589-596.
17. Fine, C., From scanner to sound bite: Issues in interpreting and reporting sex
differences in the brain. Current Directions in Psychological Science,
2010. 19(5): p. 280-283.
18. Fine, C., Neurosexism in functional neuroimaging: From scanner to pseudo-science
to psyche, in The Sage Handbook of
Gender and Psychology, M. Ryan and N. Branscombe, Editors. 2013, Sage:
Thousand Oaks, CA. p. 45-60.
19. Kaiser, A., et al., On sex/gender related similarities and
differences in fMRI language research. Brain Research Reviews, 2009. 61(2): p. 49-59.
20. Cheslack-Postava, K. and R.M.
Jordan-Young, Autism spectrum disorders:
Toward a gendered embodiment model. Social Science & Medicine, 2012. 74(11): p. 1667-1674.
21. Fine, C., Explaining, or sustaining, the status quo? The potentially
self-fulfilling effects of ‘hardwired’ accounts of sex differences.
Neuroethics, 2012. 5(3): p. 285-294.
22. O’Connor, C. and H. Joffe, Gender on the Brain: A Case Study of Science
Communication in the New Media Environment. PLoS One, 2014. 9(10): p. e110830.
to Cahill response
1. Clayton, J and Collins, F (2014) NIH to
balance sex in cell and animal studies. Nature, 509: 283.