Brains of girls and boys develop more alike than previously thought, so cognitive differences are probably more nurture than nature

This is a very interesting new Dutch study by Wieringa et al with an even more interesting conclusion:

In conclusion, the results of this study do not support the hypothesis of sex difference in cortical development trajectories. The only structure showing a sex difference in cortical maturation did not relate to sex differences in cognition. We did, however, extend previous findings of greater variability in male brain structure by showing greater male than female variability in cortical develop- ment. Observed performance differences in cognition may be related to training and educational experiences, an important question to address in future research.

Does this mean that there are no differences between the brains of boys and girls? No, there are, e.g. males brains are bigger on average and there is more variance in brain structure with males than females. But the most important finding of this study is this:

These results show that sex differences in variance are present in the absence of average sex differences in brain structure. Furthermore, behavioral outcomes favored girls for reading and boys for mental counters working memory, but these results were not consistently related to brain development trajectories. The latter finding may suggest that average sex differences in cognition are more strongly related to experience than biological predispositions.

Does this mean more nurture than nature? See also:

Taken together, we observed sex differences in behavioral cognitive performance and sex difference in brain variance, but no evidence for a relation between these two patterns.

I do think there is still also a possible nature-part than can be overlooked: the part that was inherited. But gender differences in this case do seem more nurture than nature.

Abstract of the study:

Although male brains have consistently reported to be 8–10% larger than female brains, it remains not well understood whether there are differences between sexes (average or variance) in developmental trajectories. Furthermore, if sex differences in average brain growth or variance are observed, it is unknown whether these sex differences have behavioral relevance. The present longitudinal study aimed to unravel sex effects in cortical brain structure, development, and variance, in relation to the development of educationally relevant cognitive domains and executive functions (EFs). This was assessed with three experimental tasks including working memory, reading comprehension, and fluency. In addition, real-life aspects of EF were assessed with self- and parent-reported Behavior Rating Inventory of Executive Function scores. The full data set included 271 participants (54% female) aged between 8 and 29 years of which three waves were collected at 2-year intervals, resulting in 680 T1-weighted MRI scans and behavioral measures. Analyses of average trajectories confirmed general age-related patterns of brain development but did not support the hypothesis of sex differences in brain development trajectories, except for left banks STS where boys had a steeper decline in surface area than girls. Also, our brain age prediction model (including 270 brain measures) did not indicate delayed maturation in boys compared with girls. Interestingly, support was found for greater variance in male brains than female brains in both structure and development, consistent with prior cross-sectional studies. Behaviorally, boys performed on average better on a working memory task with a spatial aspect and girls performed better on a reading comprehension task, but there was no relation between brain development and cognitive performance, neither for average brain measures, brain age, or variance measures. Taken together, we confirmed the hypothesis of greater males within-group variance in brain structures compared with females, but these were not related to EF. The sex differences observed in EF were not related to brain development, possibly suggesting that these are related to experiences and strategies rather than biological development.

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