As in, the plural of "hippocampus" - "a complex neural structure (shaped like a sea horse) consisting of grey matter and located on the floor of each lateral ventricle; intimately involved in motivation and emotion as part of the limbic system; has a central role in the formation of memories." [Definition courtesy of Princeton people]
And I would direct everyone to read this article, wth its very many interesting points. Namely, we all have the potential to be geniuses/genei (both words are acceptable, apparently). And that the Nature v Nurture debate has no clear winner.