The book "Coming Apart" comes to mind. It doesn't need to just be that we are all getting more clever. Our distribution could be increasing in part due to the e

The book "Coming Apart" comes to mind. It doesn't need to just be that we are all getting more clever. Our distribution could be increasing in part due to the effect of sending every small town genius to Harvard. This distribution has a hard cut off at the bottom end (can't get laid without a car or a job) but it doesn't have a hard one at the top end, so the effect is a more and more diverse humanity. Another possible explanation is immigration, which selects for people that can do paperwork really well; at least in America.