A study looked at patterns of migration and the prevalence of the gene DRD4 (which is one of the ADHD genes). The study found that out of the cultures that had macro-migration (migrating long distances) had a higher proportion of long alleles for DRD4. The proportion of long alleles for DRD4 in this group was .85. In the micro-migration cultures (where cultures were sedentary or nomadic), the proportion of long alleles for DRD4 was .52. It may be that impulsivity and novelty-seeking played a part in who was making long treks to unknown parts of the world. This study was published in 1999, but the data was reviewed again at the 2007 CHADD conference.
(Chen, et al., 1999, Population Migration and the Variation of Dopamine D4 Receptor (DRD4) Allele Frequencies Around the Globe. Evolution and Human Behavior, 20(5), 309-324.)
On a related note, I’ve been researching my family’s genealogy, and found that one of my ancestors who lived in Massachusetts in the 1600s had a little impulsivity problem. At one point, he rode through town telling everyone they should rebel against the English government (Granted, years later this method worked during the Revolutionary War. So my ancestor was ahead of his time!). The English didn’t like that too much, and he was shipped back to England where he did some jail time at the Tower of London. He then came back to Massachusetts. There is actually documentation that his impulsivity was still alive and well. So there you go. My family’s ADHD has been traced back to the 1600s.