The most profound difference between girls and boys is not in any brain structure per se, but rather in the sequence of development of the various brain regions. The different regions
of the brain develop in a different SEQUENCE in girls compared with boys -- this is the key insight from recent research in brain development. The world's largest study
of brain development in children, an ongoing longitudinal study conducted at the National Institutes of Health in Bethesda, Maryland -
clearly demonstrates dramatic differences in the trajectories of brain development in girls and boys, with more than two standard deviations of difference separating girls from boys at age 11,
for example - an age at which there is almost NO difference in average height between girls and boys. So, these sex differences in brain development cannot be attributed to sex differences in overall size, as these
researchers themselves emphasize this point (Lenroot et al., p. 1070). You can download the full text of this
NIH study (Lenroot et al.) by clicking here.
The NIH/NIMH study, entitled "Sexual dimorphism of brain developmental trajectories during childhood and adolescence," is reprinted by permission of Elsevier
from the journal
NeuroImage, volume 36, number 4, pages 165-173, July 15 2007.
Why is this so important? Here's why. If you teach the same subjects to girls and boys in the same way, then by the age of 12 or 14, you will have girls who think "geometry is tough" and boys who believe "art and poetry are for girls."
The lack of understanding of gender differences has the unintended consequence of REINFORCING gender stereotypes. Conversely, if you understand these differences, you can break down gender stereotypes. This principal
and its relationship to the underlying brain research is explained at greater length in chapter 2 of the book
Boys Adrift (Basic Books, 2007/2009).
More recently, the same team at NIH has released a short video illustrating these sex differences in the developing brain. You can link to the video at no charge
via this link at the Psychology Today web site, "Unexpected sex differences in brain development."
Despite the title of that Psychology Today post, the findings from the NIH/NIMH group were not truly unexpected. Harriet Hanlon and her associates at Virginia Tech had previously examined brain activity in 508 normal children
-- 224 girls and 284 boys -- ranging in age from two months to 16 years. This study, the largest and most carefully executed of its type, demonstrated striking and consistent sex differences in the speed with which the brain matures.
It also showed that boys' brains develop differently than girls' brains do. It's not correct to say, "boys develop along the same lines as girls, only more slowly." The truth is more nuanced.
These researchers found that while the areas of the brain involved in language and fine motor skills mature about six years earlier in girls than in boys,
the areas of the brain involved in targeting and spatial memory mature about four years earlier in boys than in girls. These researchers concluded that the areas of the brain involved in language, in spatial memory, in motor coordination,
and in getting along with other people, develop in a "different order, time, and rate" in girls compared with boys.
Source: Harriet Hanlon, Robert Thatcher, and Marvin Cline. Gender differences in the development of EEG coherence in normal children. Developmental Neuropsychology, 16(3):479-506, 1999. The quotation comes from page 502.
Similar results were reported in a smaller study by A. P. Anokhin and associates: Complexity of electrocortical dynamics in children: developmental aspects. Developmental Psychobiology, 36:9-22, 2000.
That conclusion, that different areas of the brain develop in a different sequence in girls compared with most boys, is supported by other studies looking at specific skills in young children. For example: Jean Christophe Labarthe in Paris, France watched two-year-olds building bridges out of blocks. At that young age, he found that a boy is about three times more likely than a girl to be able to build a bridge out of blocks.
Source: Jean Christophe Labarthe. Are boys better than girls at building a tower or a bridge at 2 years of age? Archives of Diseases of Childhood, 77:140-144, 1997.
On the other hand, researchers at Wellesley College found that 3-year-old girls could interpret facial expressions as well or better than 5-year-old boys could.
Source: Chris Boyatzis, E. Chazan, C. Z. Ting. Preschool children's decoding of facial emotions. Journal of Genetic Psychology, 154:375-382, 1993.
So, it's too simple to say that boys mature more slowly than girls do. Boys mature faster than girls in some areas, slower in others.