According to a paper to be released in the September issue of the journal “American Naturalist”, the number of sperm a male ejaculates may be correlated to his attractiveness as measured by the females in the population. The idea came forth after scientists at University College London and the Oxford University mathematically modeled the optimal “sperm load” to maximize daddiness across a range of mating patterns. The research, which took place late one Friday night at the corner bar, was one of several proposed ideas to “settle a bet” between two of the scientists.
The results suggest that males who attract more females may produce fewer sperm per mating than those who aren’t so lucky. Essentially, the model shows that the optimal way to get lots of offspring is to mate with as many females as possible, even if those matings involve fewer sperm and, thus, a lower probability of conception per ‘bow chicka bow wow’. Conversely, males with fewer opportunities to mate should put all their sperm in whatever baskets they can woo. This increases the probability of conception per mating, an advantage when you can’t get much.
This idea is in contrast to the assumption that higher quality males are more fertile. The authors recognize that the pattern may not hold true for all species, given the diversity of mating strategies across taxa. They also state that it is difficult to know how these findings apply to humans and other primates. However, we all know that was just a CYA statement and, in actuality, they nailed it.
Future studies will focus on comparing sperm load in males that are similarly attractive but with differing access to prime sperm-making resources. The authors do not mention which species will have the joy of settling this bet, but the odds of the results being apt for Homo sapiens are about 100:1.
Fig. 1 A schematic representation of optimal sperm load by relative attractiveness
‘The evolution of continuous variation in ejaculate expenditure strategy’ by S. Tazzyman, T. Pizzari, R. Seymour, and A. Pomiankowski will be published in the September issue of the journal American Naturalist.