This may be related. I read in one of the BP books that there has been a higher disposition to BP in our country (USA) due to 'sampling error' of those who have colonized our country in general. The idea is that the BP type person, with the risky hypomania... would be more likely to pick up and move to the frontier. Now I like the idea of this... and it seems plausible. But I don't know. There were so many reasons people came here.

If it IS true and we do have a higher number of BP folks then there could be some mechanism by which they are increasing in a relative proportion. We do like sex. ;-)