While it is almost certain that intelligence ahs a neurological basis, the extent to which intelligence is determined by neurological and chemical changes is not fully understood. A recent study suggests that changing hormone levels prior to and during puberty have a large effect on intelligence; high salivary testosterone levels in ten-year-old boys showed a positive correlation with intelligence, but a negative correlation in twelve-year-olds (Shangguan & Shi 2009). This shows that intelligence can be quite fluid, and can even be affected quite differently by the same mechanisms. The exact nature of the changing influence testosterone seems to provide or signal is not known, but the correlation demands further study.

These three different research studies display very different theories of intelligence. In the first study, accepted methods of cognitive relationships with the environment are valid, if perhaps somewhat inaccurate at the extremes of the intelligence spectrum. The second study points...
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