More Alike Than Different Than Are Unaffected Children

COMMENT BOOKS & ARTS

But, as both authors point out, the reported differences in corpus callosum size are unre- liable between studies, and seem to be related

H. PYLE/CORBIS to brain size. In both sexes, larger brains have a larger callosum, but in smaller brains they make up a greater percentage of brain vol- ume. So if a sex difference in the corpus callosum exists, it is likely to be a by-product of the basic difference in average brain size — a fact that is missed by a focus on sex. Unless researchers conduct analyses that divide groups in ways other than gender, the real story might be missed. The behaviours of both sexes are remark- ably similar despite their presumed brain and hormonal differences. Although men’s brains are roughly 10% larger than women’s, the IQs of both genders are roughly equal, and most experiments in cognitive processing in children and adults reveal no sex differences. In deflating spurious claims about the influences on sex differences, the books risk PSYCHOLOGY underestimating those effects. Consider con- genital adrenal hyperplasia (CAH), a major topic in Jordan-Young’s book, in which the fetus is exposed to higher levels of androgens More alike than different than are unaffected children. This causes emotional and physical symptoms ranging Two books debunk gender differences in the brain, in girls from early-onset puberty to infertil- discovers Virginia Valian. ity. Jordan-Young concludes that children with and without CAH are more alike than different. But in my view, she underestimates rying to distinguish the female from Delusions of Gender: How Our Minds, the differences between girls with CAH and the male brain is a trap that many Society, and Neurosexism Create their unaffected peers in two domains. writers fall into. Two books provide a Difference/The Real Science Behind Sex Although the data are mixed, girls with Differences Twelcome corrective by reviewing scientific CAH seem to be better at mentally rotating CORDELIA FINE evidence showing that the sexes are more W. W. Norton/Icon Books: 2010. 338 pp./368 pp. shapes than are unaffected girls. The results alike than different, and that small sex differ- $25.95/£14.99 are clearer for toy preferences: when asked to ences are not fixed but change with context choose from various ‘masculine’, ‘feminine’ Brain Storm: The Flaws in the Science and across generations. of Sex Differences and ‘neutral’ toys, girls with CAH show more Cordelia Fine’s Delusions of Gender is REBECCA M. JORDAN-YOUNG interest in masculine and less interest in fem- aimed at a broad audience and debunks the Harvard University Press: 2010. 408 pp. $35 inine toys than girls who are unaffected. Boys egregious exaggerations common in popular with and without CAH are indistinguishable books. Rebecca Jordan-Young’s Brain Storm Although males and females differ in in their choices. is directed at specialists who are interested in many ways, the authors note that the same Whether a toy is perceived as masculine historical studies of the brain, sex hormones could be said of any two groups — people or feminine, however, depends on who plays and gender differences. Fine, a psychologist with different hair colour or degrees of with it; as Jordan-Young notes, children’s at Macquarie University in Sydney, Australia, economic security, say. Because men and play preferences have changed over time. and Jordan-Young, a medical sociologist at women have distinct reproductive functions, Some activities once seen as masculine, such Barnard College in New York, point out the controlled in part by different hormones, we as playing with construction toys and balls, methodological and theoretical limitations are prone to interpret their behavioural and are now seen as neutral and on a par with of such studies, and demonstrate the part psychological differences as not only biologi- books and puzzles. Dolls, by contrast, have that folk theories about gender differences cally mediated but mandated. Putative brain remained feminine. Toy-preference stud- have played in casting the sexes as inherently differences are seized on as sex-based and ies show that girls divide their time equally dichotomous. other hypotheses can be overlooked. among masculine, feminine and neutral Both books note that correlation and cau- To illustrate, Fine considers the corpus cal- toys, whereas boys tend to eschew feminine sation are often confused when looking at the losum linking the two brain hemispheres. The ones. So the girls with CAH are acting like results of brain or hormonal differences on fact that it seems to be thicker in women than control boys. But we cannot tell whether that behaviour — ‘causing’, for example, boys to in men is sometimes associated with women’s is because they prefer masculine toys or are be better than girls at mental rotation of three- supposed greater verbal skill. According to taking less interest in feminine ones. The dimensional objects. Too many studies ignore this ‘just-so’ reason- way such questions are posed affects where mediating variables and alternative explana- NATURE.COM ing, a thicker corpus one searches for answers. tions and exaggerate the extent of gender dif- Neurobiologist Ben callosum may allow So why do boys avoid dolls? They learn ferences. Both accounts direct attention to Barres on gender and easier integration of early that they will pay a social price for the full range of results, including those that science: information from the showing ‘deviant’ feminine interests. Girls researchers might otherwise ignore. go.nature.com/pdo9ax two sides of the brain. can like the same toys as boys with little fear

332 | NATURE | VOL 470 | 17 FEBRUARY 2011 © 2011 Macmillan Publishers Limited. All rights reserved BOOKS & ARTS COMMENT of negative social consequences, as demon- infancy. Laying such distinctions only at the between a behaviour and a set of neural strated by the different connotations of ‘sissy’ doorstep of social psychology — in different mechanisms. Different neural mechanisms and ‘tomboy’. For girls with CAH, there is expectations of the two sexes, for example — can be responsible for the same behaviour. another social issue: many undergo genital closes off inquiry into underlying cognitive It is no bad thing that there are many surgery in infancy and have impaired fertility. processes. Similarly, there is almost nothing hypotheses still to test. Eventually, unsup- Girls’ knowledge about their condition may about sex differences in mathematics and ported preconceptions about what counts as trigger concerns about their femininity and science in Jordan-Young’s book, and only a masculine and feminine will be discarded. lead to an avoidance of toys such as dolls. cursory treatment in Fine’s. Until then, people such as Fine and Jordan- To some extent, both books are brooms I share both authors’ conclusions that the Young are just who we need. ■ that sweep too clean. I contend that one jury is still out over whether hormonal and cannot dismiss sex differences in mental neural sex differences are linked to behav- Virginia Valian is professor of psychology rotation of three-dimensional objects as ioural divergence. I also agree that social and co-director of the Gender Equity Project ill-documented or easily reversed, as both context is often a more likely source of sex at Hunter College, City University of New authors do. The difference is robust and dif- differences. Most behavioural sex differences York, New York 10065, USA. ficult to neutralize; its precursors are seen in are small, and there is no direct mapping e-mail: [email protected]

ASTRONOMY covered up. Lautaro is an older archaeologist who followed the trails of ancient civiliza- tions through the desert for decades, find- ing their mummified dead in the desiccating Answers from the atmosphere. Now he teaches the searching women how to recognize from the surface grains whether a human body might lie Atacama below the sand. Also featured is Luís. He spent years in one A Chilean film juxtaposes astronomy with the search for of Pinochet’s concentration camps in the des- those killed under Augusto Pinochet, finds Alison Abbott. ert, where he learnt about astronomy from a fellow political prisoner. Stargazing helps him not to forget that time, he says. Miguel, he Atacama Desert in northern Chile an architect, survived five such camps. He is the driest place on Earth. Dec- committed their layouts to memory and ades can pass with no rain. Patricio drew them up precisely when he was freed, TGuzmán tells the stories of the people who so that Chileans would never be able to deny are searching in its arid expanse in his film their existence. Nostalgia de la Luz (Nostalgia for the Light) Towards the end of the dictatorship, — winner of the 2010 European Film Acad- Pinochet’s soldiers dug up mass graves and emy award for best documentary and now dumped evidence of the massacres in the sea. showing in selected cinemas in Europe. On The film follows Victoria and Violeta, who the desert’s mountain tops, astronomers talk movingly about their continuing search look skyward, hunting for cosmological for their loved ones. They have found frag- truths. On its plains, others look towards the ments of their bones, smashed by the digging ground, hunting for political truths. machinery, which has fed their determina- Astronomers love the Atacama. Its dryness tion to find out what happened. and clear skies give them an unimpeded view And there is Valentina, whose mother and of deep space. Since the mid-1960s, they have father were among those who disappeared, been building ever-more powerful telescopes who became an astronomer after the grand- there with which to gaze ever farther into the parents who raised her taught her to observe cosmos. Piecing together the history of the the night sky. Understanding the infinite Universe from the ancient light of distant Universe, she says, has given her a comfort- stars, they are largely unaware of the women ing perspective on her loss. below on the desert floor, digging — some- Guzmán, the film’s director, is himself a Nostalgia de la Luz times with their bare hands — for the remains DIRECTED BY PATRICIO GUZMÁN refugee from Pinochet’s Chile, and now lives of loved ones killed during the regime of dic- In some independent cinemas in Europe. in France. Most of his films have been politi- tator Augusto Pinochet in the 1970s. cal, and this venture into science provides Nostalgia de la Luz interweaves the stories came from, where we are going and how we him with metaphors of immense power of these two searches — one addressing mod- come to terms with the pain of the present. It with which to explore this theme. Nostalgia ern history on a heartbreakingly human scale, is compelling, thanks to the characters that the de la Luz will also confront scientists with the other deep history on a grandiose and director has found to explain their quests. connections that they have not previously edifying scale. Other scientific investigations Gaspar is an articulate young Chilean imagined. If only, the searching women also feature, including astronomer working at the Cerro Tololo say, the telescopes could instead point archaeology. It is a slow, NATURE.COM observatory, who can answer many ques- downwards to help them. ■ poetic film that con- For more on the spirit tions about cosmic history but few about his templates existential of observatories: country’s recent past, when thousands disap- Alison Abbott is Nature’s European questions: where we go.nature.com/ehdIon peared or were killed and traces of their fate correspondent.