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Biological Sex Differences

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  1. Are boys’ and girls’ brains hardwired for different abilities?
  2. How do boys' and girls' brains differ?
  3. Do sex hormones affect learning?
  4. Do boys and girls learn differently?

Are boys’ and girls’ brains hardwired for different abilities?  

Modern neuroscientists believe that the brain is not specially hardwired for any higher mental ability. Gender differences in the brain are small and likely magnified by experience.

Boys and girls are obviously different, but this doesn’t mean their brains are prewired that way. In fact, there is little our brains do that is fixed at birth, beyond the most basic reflexes and physiological responses. Even the simple ability to see is critically dependent on early experience: The rare baby who is born with serious eye problems can remain permanently blind if treatment is not initiated in the first few months, because of the fact that the visual brain (occipital lobe) requires normal visual experience from birth to wire up properly.

Similarly, gender differences reflect the interaction of nature and nurture from the earliest days of life. Boys and girls are not identical at birth, but their small differences soon become magnified by parents, grandparents, teachers, peers, and a larger culture that sees them as two very different types of people. For example, girls do talk a bit earlier than boys, and they are an average of one month more advanced in verbal skills through the second year of life;1 however, parents also talk more to their daughters,2 and girls talk more to their friends, giving girls additional practice and widening their verbal advantage during early childhood.

Research on expert performance finds that it is practice (10,000 hours!) more than raw talent that determines who ends up on top of a particular field. No matter what the skill – speaking, reading, writing, calculating, drawing, singing, batting, running – a child’s neural circuits need lots and lots of practice to optimally acquire it.

The belief in “hardwired” gender differences is not only wrong, it is harmful to children. Whether male or female, assuming that a child’s abilities are fixed from birth defeats the purpose of education, which is to cultivate a wide range of cognitive and interpersonal abilities, regardless of his or her initial interests and strengths.

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1 Fenson, L., Dale, P. S., Reznick, J. S., & Bates, E. (1994). Variability in early communicative development. Monographs of the Society for Research in Child Development, Serial No. 242, Vol. 59.

2 Leaper, C., Anderson, K. J., & Sanders, P. (1998). Moderators of gender effects on parents' talk to their children: A meta-analysis. Developmental Psychology, 34, 3-27.

How do boys' and girls' brains differ?

Neuroscientists have identified a few differences between boys’ and girls’ brains, but none have been linked to learning or behavioral differences.

Despite many popular claims about boy-girl brain differences, surprisingly little has been scientifically proven. We know that boys’ brains are about 10% larger than girls’, similar to the brain size difference between adult men and women. But males also have larger hearts, kidneys, and lungs compared to females, and males are heavier and taller except for a brief phase at the onset of puberty. Bigger bodies require bigger organs, so it is unlikely that this simple brain size difference accounts for behavioral differences between boys and girls.

We also know that in adolescence, girls’ brains finish growing about 1-2 years earlier than boys’.1 Again, this matches male-female differences in physical development, but has no known relationship to boy-girl behavioral differences. In fact, everything we know about male development suggests that boys’ frontal lobes – which are responsible for planning, organization, and self-control – must mature a bit slower than girls; however, the best brain-wave data find exactly the opposite – faster maturation in boys.2  

More reliable brain sex differences have been found in adults, but even here, scientists do not yet understand how a finding like women’s larger proportion of gray matter relates to any particular behavioral difference. In general, sex differences are more prominent in lower brain structures, such as the hypothalamus (which controls basic drives like hunger, thirst, and sexual reproduction itself), and less prominent in higher brain structures, including the cerebral cortex, which control our more sophisticated and reasoning and social-emotional abilities.

Very often, single-sex school advocates use evidence of differences between adult men’s and adult women’s brains to make claims about boys and girls. This is highly misleading, because the brain itself is changed by experience. Researchers who find a difference between men’s and women’s brains simply cannot know whether that difference is the product of nature (that is, genes or hormones) or nurture – the 20+ years of growing up and living as male or female that the adult research subjects (usually college students) experienced before lying down in the MRI scanner.

In fact, most evidence suggests that boys’ and girls’ brains start out just a little bit different, but then grow more distinct as a result of their very different life experiences. That’s why, if we really want to reduce gaps between them, boys and girls need more, rather than less, interaction and opportunities to share, play, collaborate, compete, and learn together.

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1 Lenroot, R. K., Gogtay, N., Greenstein, D. K., Wells, E. M., Wallace, G., et al. (2007). Sexual dimorphism of brain developmental trajectories during childhood and adolescence. NeuroImage, 36, 1065-1073.

2 Barry, R. J., Clarke, A. R., McCarthy, R., Selikowitz, M., Johnstone, S. J., et al. (2004). Age and gender effects in EEG coherence: I. Developmental trends in normal children. Clinical Neurophysiology, 115, 2252-2258.

Do sex hormones affect learning?

Boys’ exposure to testosterone before birth biases certain physical and play preferences, but sex hormones after birth have very modest, if any, effects on thinking and learning skills.

Sex hormones are an important factor in development. Elevated levels of testosterone before birth are critical for shaping the male body, and they also influence, to a degree, boys’ later behavior. Solid scientific evidence indicates that prenatal testosterone biases boys’ toy preference, higher activity levels, and penchant for rough-and-tumble play. On the other hand, studies searching for effects of prenatal testosterone on thinking and learning skills have come up largely negative.1

After birth, hormone levels decline to very low levels in both boys and girls, a period called the “juvenile pause” that lasts until the onset of puberty. Hormone levels rise again after puberty. Despite considerable research, there is little evidence that fluctuations in estrogen, progesterone, or testosterone levels affect adolescent learning. As you might expect, sex hormones have a greater effect on reproductive behavior, but little impact on thinking or reasoning skills.

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1 Hines, M. (2007). Do sex differences in cognition cause the shortage of women in science? In S. J. Ceci & W. M. Williams (Eds.), Why aren't more women in science? (pp. 101-112). Washington, DC: American Psychological Association.

Do boys and girls learn differently?

No. The idea of different learning styles has been discredited by scientific evidence. Boys and girls learn using similar mental and brain processes.

The notion that boys and girls learn differently has become very popular with teachers and parents, but is not supported by actual scientific studies of learning. Some claim, for example, that boys are “visual learners,” whereas girls are “auditory learners.” It is true that females’ hearing is a tiny bit better than males’, but only if you’re measuring the absolute-quietest detectable sound in an otherwise noiseproof laboratory. In any real-world classroom or gymnasium, there is no meaningful difference between males’ and females’ auditory perception, and both sexes are perfectly capable of learning through their ears – especially if they are taught to take notes while listening. Similarly, there are no meaningful differences between boys’ and girls’ vision, aside from the fact that some 8% of boys are colorblind, compared to 0.5% of girls. If boys and girls choose to draw pictures in different colors, it is much more a reflection of what they see on Saturday morning cartoons than any sex difference in their retinas or occipital lobes.

In fact, the whole notion of “learning styles,” another educational fad that is now being applied to gender differences, has failed to hold up under scientific scrutiny.1 The truth is that boys and girls are far more similar than different in their ability to process, store, and recall information at a later time. In addition, psychologists and neuroscientists have not discovered any reliable differences between boys' and girls' mental or neural processing as they learn how to speak, read, or memorize their multiplication tables. The brain mechanisms of learning appear overwhelmingly similar between boys and girls, as well as between men and women.

Learning takes motivation, repetition, and engagement. The magic recipe differs for every child and can best be met by teachers who are sensitive to individuals’ needs, regardless of gender, race, or other category memberships. 

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1 Pashler, H., McDaniel, M., Rohrer, D., & Bjork, R. (2009). Learning styles: Concepts and evidence. Psychological Science in the Public Interest, 9, 105-119.