Gender Differences

Gender stereotyping is a very interesting, important, and complex subject.  Stereotype is defined as “a standardized mental picture that is held in common by members of a group and that represents an oversimplified opinion, prejudiced attitude, or uncritical judgment” (Merriam-Webster Online Dictionary, 2010).  Thus, stereotyping is oversimplified, uncritical, and perhaps even prejudiced.  It also lumps all members of the group into the same simplistic judgment.  On its face, stereotyping is wrong.

Our society has entertained many gender stereotypes over its history.  Most were directly prejudicial to women.  The most recent swing of the pendulum brought the culture to a belief in androgyny, a belief that all Homo sapiens have “the characteristics or nature of both male and female” (Merriam-Webster Online Dictionary, 2010).  However, recent neurobiological research demonstrates that this cultural assumption, however laudably equitable, is simply not correct.

A recent NIH/NIMH study found that “robust sex differences in developmental trajectories were noted for nearly all (brain) structures” (Lenroot et al., 2007).  The study also noted “peak gray matter volumes generally occurring earlier for females” and that “mean total cerebral volume was approximately 10% larger in males.  Total cerebral volume peaked at 10.5 years in females and 14.5 years in males” (Lenroot et al., 2007).  Thus, on average, male brains are larger than female brains and both total brain volume and gray matter volumes peaked 1 ½ to 2 years earlier in females than males.

A different study found that “girls rely on a supramodal language network, whereas boys process visual and auditory words differently” (Burman, Biten, & Booth, 2008).  In other words, females use different parts of their brain to process language and do so in a different fashion than males. 

With the recent developments in modern neural imaging technology, brains can be observed as never before.  A flood of research is revealing many new facts about how our brains work.  Many of those facts are revelations about how distinct average male and female brains really are.  One other study I would like to note is from a different field.  This study examined prenatal stress in rats and its effect on “latent inhibition (LI),” a Pavlovian conditioned response.  Fascinatingly, “prenatal stress increased the amount of LI only in the males” (Bethus, Lemaire, Lhomme, & Goodall, 2005).  In this pre-natal (i.e. almost entirely social influence free) study, female rats were unaffected. 

The body of evidence is large and growing larger that, on average, males and females have significant neurobiological, developmental differences.  Some are only in the timing of development, some are in structure and processing.  To be sure, there are no claims or assumptions of superiority for either gender.  However, unfortunately the easier and morally simpler assumption of androgyny is simple incorrect.  Unfortunately, there will be no simple answers in the area of gender differentiation.

Lenroot et al. (2007) sum it up nicely: “Differences in brain size between males and females should not be interpreted as implying any sort of functional advantage or disadvantage.  Size/function relationships are complicated by the inverted U shape of developmental trajectories and by the myriad factors contributing to structure size, including the number and size of neurons and glial cells, packing density, vascularity, and matrix composition.  However, an understanding of the sexual dimorphism of brain development, and the factors that influence these trajectories, may have important implications for the field of developmental neuropsychiatry where nearly all of the disorders have different ages of onset, prevalence, and symptomatology between boys and girls” (Lenroot et al., 2007, p. 1072).
 

References

Bethus, I., Lemaire, V., Lhomme, M., & Goodall, G. (2005, March 30). Does prenatal stress affect latent inhibition? It depends on the gender. Behavioural Brain Research, 158(2), 331-338. doi:10.1016/j.bbr.2004.09.013
Burman, D., Biten, T., & Booth, J. (2008, January 4). Sex differences in neural processing of language among children. Neuropsychologia, 46(5), 1349-1362 . doi: 10.1016/j.neuropsychologia.2007.12.021 Retrieved from
Lenroot, R., Gogtay, N., Greenstein, D., Wells, E., Wallace, G., Clasen, L., Blumenthal, J., … Giedd, J. (2007, March 17). Sexual dimorphism of brain developmental trajectories during childhood and adolescence. NeuroImage, 36, 1065-1073. Retrieved from http://www.boysadrift.com/2007Giedd.pdf
Merriam-Webster Online Dictionary. (2010). Androgyny. Retrieved February 25, 2010, from http://www.merriam-webster.com/dictionary/androgyny
Merriam-Webster Online Dictionary. (2010). Stereotype. Retrieved February 25, 2010, from http://www.merriam-webster.com/dictionary/stereotype

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