Upon researching the topic I've become a lot less worried about any such effect but I wanted to describe some weakness in the theory I saw off the top of my head:
- People with low IQs might have more babies but they die young more often, so it's a wash
- People with high IQs don't necessarily have to reproduce more just so long as they recruit more. IE, they support progressive policies that help uplift others and make them reach their intellectual potential.
- As we gain more knowledge about genetics we draw closer to the end of evolution as we know it. IE, in the future if you think your baby is going to be dumb you'll just go to a doctor and have them fix it.
- If the effect were ever to become manifest it's highly improbable that it would effect the whole world equally. One society would figure out a way around it and would end up invading and taking over the rest.