While in this case, I've heard it before and it seems to come from actual scientists, so it's probably not just a journalist's imagination. But in general, I ag

While in this case, I've heard it before and it seems to come from actual scientists, so it's probably not just a journalist's imagination. But in general, I agree that it's frustrating to read articles about trends which don't show numbers, particularly graphs, making it difficult to judge. There are so many articles making scary claims like "X has dropped to half what it was a decade ago!" but it turns out that X fluctuates wildly anyway and the recession or whatever had a massive temporary effect on it. That said, my 2c is that high IQ causes people to become professionals and being a professional reduces the number of children they have. From my personal observations, poor people seem to have children as their purpose in life while professionals have other purposes and don't feel as much need for children. Contrast this to most of the last couple of millennia where the highest status men had lots of children to multiple mothers, and famines were common, which would wipe out the poorest people. The poorest people would have included those least able to climb the class hierarchy by being merchants or intelligently winning the games of politics. There also wasn't social welfare to enable the poorest people to support as many children as they want. It sounds like a breeding ground for intelligence.