The size of the brain is established at an early age, with the
whole brain volume at 95% of its adult size by the age of 4. However,
the brain continues to develop through the teen age, with many of these changes
being sex specific. In the adult brain, the overall cerebral size is larger in men than women,
but there are specific parts that are larger in women. These include the caudate nucleus,
some prefrontal cortical regions, superior temporal gyrus,
and some white matter structures such as the anterior commisure .
In the male, the hypothalamus, stria terminalis, cerebral ventricles,
and the splenium and genu of the corpus callosum are proportionally larger.
In regions where the volume of the structure may not be different, there may be a difference in neuron density.
For example, a region of the suprachiasmatic nucleus contains twice as many neurons in men until
middle age, when the sex difference reverses and then ultimately disappears.
Frederikse et.al. found sex differences in the inferior parietal lobule (IPL) of the brain (the IPL is shown in yellow in the above diagram). The IPL, a neocortical region, is part of the heteromodal association complex (HASC), which includes the Broca's area among other parts. The IPL is believed to have a role in processing information from the visual, auditory and somatosensory association cortices as well as having connections with other HASC regions, the limbic system and the hypothalamus. In their study of 15 pairs of normal male and female subjects, Frederikse et.al. concluded that men have a larger total IPL volumes than women, with this difference primarily as a result of a larger left male IPL volume. This study supports previous evidence that men tend to outperform women on tasks of visuospatial processing, a function primarily of the left side of the IPL.
Research found that men tend to use one side of their brain (particularly the left side for verbal reasoning) while women tend to use both cerebral areas for visual, verbal and emotional responses. These differences in brain use cause a difference in behavior between men and women. Women tend to be better at sensing emotional messages in conversations, gestures, and facial expressions, and are thus more sensitive. Women start to speak and read at an earlier age than men and are generally better in verbal skills, such as learning a different language. They tend to have a better grasp on grammar and spelling, and girls have better handwriting than boys do. Women have better sight at night and have a more acute sense of smell, taste and hearing.
Men are better in spatial coordination and have a better sense of direction (usually!). They excel in math and are great at interpreting three-dimensional objects. They have a better hand-eye coordination and more precise control of large muscle movement. They have poor peripheral vision but better sight in bright light and a better sense of perspective. Since they use one side of their brain more than the other, they tend to use the left side for verbal reasoning and the right for visual and emotional activities (if they are right handed).
These differences are not rules. It is easy to find women who excel in math and men who have excellent language skills (and it is even easier to find men with no sense of direction). Chances are the above statements are not going to work for your everyday situation, but these have been shown to be true in scientific studies, based on large, diverse populations. When looking at large populations, these differences between men and women become evident, and proper statistical analysis takes care of the exceptions.
Differences in brain structure cause very interesting difference in behavior and are thus important to the paleoanthropological study of humans. It is often these variations in behavior that aid researchers in determining the functions of brain areas. Whether these could be correlated to behavior will depend on the way the study is performed, but anthropologists should take the variations between men and women into consideration as they study human societies.