Moyzis and his team decided to look at the gene closely, and what they found surprised them. There are more than 10 different versions of the DRD4 gene, but by far the oddest is the one associated with ADHD. By analyzing its structure and comparing it with the other versions, they concluded that the variation must have occurred suddenly, rather than evolving over many years. What's more, says Moyzis, "the genes adjacent to the variant DRD4 were almost exactly the same, whether in an individual from Africa, America, or Europe." Since genes constantly rearrange themselves and mutate at a certain rate, an ancient variation should have been surrounded by many different combinations of genes among different people. Consequently, he reasoned, the gene must have sprung up sometime in our recent history.