Findings from researchers at the University of Oxford and University of College London suggest that attractive males release fewer sperm per mating in order to maximize their chances of producing offspring across a range of females.
The study is backed up by research conducted on chickens and could apply to humans as well.
The report mentioned that “the more attractive a male is, the more females will be willing to mate with him, reducing the value of each mating to him. This means it is optimal for him to contribute fewer sperm per mating.”
Less attractive males, on the other hand, secure fewer matings but value them highly, and by allocating more sperm to each mating, they in turn make the most of their meager opportunities.
This all leads to the prediction that matings with attractive males may be less fertile than those with unattractive males.
Bringing it back to how all this relates to humans…
There are many factors that can contribute to human attractiveness. “Nonetheless, ejaculate size and sperm quality are likely to have been molded by similar forces, like attractiveness and the number of sexual partners, that are important in other species.” [news.com.au]