Dim wits have a greater tendency toward sexual promiscuity and likewise have too many babies on average, when they are able to, which in general can, will and does create more dim wits. They also have trouble with simple tasks like driving many times and need a greater degree of help or assistance in order to master them. Perhaps it is something in the human genome trying to eradicate itself with the promiscuous tendencies because people generally, as a whole, are the worse sort of parasites to the "Planet Earth". The average and below average are the majority, so we are doomed any way you look at it.