The Marching Morons

In the classic 1950's sci-fi story The Marching Morons John Barlow accidentally goes into suspended animation. He awakes centuries later in a very different world where the average IQ is 45. In Cyril Kornbluth's story the human race has regressed and there are only a few intelligent humans remaining. Is this possible? I think it is. We assume that humans will continue getting smarter. But evolution has no such "plan". Evolution just happens.