A recent study, published in the Proceedings of the National Academy of Sciences, has shown that high-level mathematical reasoning rests on a set of brain areas that do not overlap with the classical left-hemisphere regions involved in verbal semantics.

Instead, all domains of mathematics tested recruit a bilateral network, of prefrontal, parietal, and inferior temporal regions, which is also activated when mathematicians or non-mathematicians recognize and manipulate numbers mentally. These results suggest that high-level mathematical thinking makes minimal use of language areas and instead recruits circuits initially involved in space and number. This result may explain why knowledge of number and space, during early childhood, predicts mathematical achievement.

In nearly all human populations a majority of individuals can taste the artificially synthesized chemical Phenylthiocarbamide (PTC). However, the percentage varies dramatically–from as low as 60% in India to as high as 95% in Africa.

That this polymorphism is observed in non-human primates as well indicates a long evolutionary history which, although obviously not acting on PTC, might reflect evolutionary selection for taste discrimination of other, more significant bitter substances, such as certain toxic plants.

A somewhat more puzzling human polymorphism is the genetic variability in earwax, or cerumen, which is observed in two varieties. Among European populations 90% of individuals have a sticky yellow variety rather than a dry, gray one, whereas in northern China these numbers are approximately the reverse. Perhaps like PTC variability, cerumen variability is an incidental expression of something more adaptively significant. Indeed, the observed relationship between cerumen and odorous bodily secretions, to which non-human primates and, to a lesser extent humans, pay attention suggests that during the course of human evolution genes affecting body secretions, including cerumen, came under selective influence.