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GENDER & SEXUAL ORIENT-
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Structural Differences between Male and Female Humans
Scientists have found some significant structural differences in the brains of males and females. For example, the suprachiasmatic nucleus (SDN) in the preoptic area of the hypothalamus is known to be a sexually dimorphic area of the brain. This means that there is some kind of difference in the structure between brains of males and females. The following drawing demonstrates how the SDN is observed:
 (image thanks to this site on the Neurobiology of Sexual Behavior)
The SDN tends to be larger in males than in females. Look at the photomicrographs of sections through the preoptic area of the brains below:
 (Note that these images are of rat brains, although our conversation will revolve around the implications for humans. Images thanks to this site on sexual behavior)
You probably noticed that in "normal males", the red area is larger than it is in "normal females". In other words, the volume of this particular group of cells is larger in males. In particular, scientists, such as Swaab (1985), found that the SDN is often 2.5 times larger in males than in females; scientists are uncertain as to whether the difference is due to increased cell number or cell size.
 Who cares?!?! Why does it matter that some individuals have larger SDNs than others?
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