(Study of war veterans)... those who performed better on intelligence tests tended to have more - and more mobile - sperm.... people with robust genes might be blessed with a biological "fitness factor" making them fit, healthy and smart. Lead researcher Dr Rosalind Arden said: "...our results do support the theoretically important 'fitness factor' idea. We look forward to seeing if the results can be replicated in other data sets, with other measures of intelligence and other measures of physical health that are also strongly related to evolutionary fitness."
But the question about intelligent people isn't why they are so reproductively fit: it's not why there are so many, but why there are so few. Cheetahs are specialised for running, and all cheetahs run very fast. The fast cheetahs have greater 'evolutionary fitness' so there aren't any slow ones any more. That is manifestly not the case with human intelligence. If intelligent men have such a reproductive advantage over unintelligent men - why are they so rare in human populations?
My guess is that sperm quality and brain development are both very dependent on maternal health and childhood nutrition, rather than being joint markers of genetic superfitness. There may also be a link between nutrition and more educated mothers etc. However, there are obvious political and social reasons why people don't want to think about that, and prefer to say there is a class of super-fit spermaniacs.
(To be fair the article quotes a guy at Sheffield university who says "The fact that it's possible to detect a statistical relationship between intelligence and semen quality in adult men probably says more about the co-development of brain and testicles when the man was in his mother's womb" Well, yeah.)