Identifying disadvantages of sperm competition is difficult. Certainly, each criterion I consider seems to be an advantage. In fact, I’ve started typing three times now and realised that I am describing an advantage.
One thing that males look for in a sexual relationship is fidelity. They need to be certain of paternity. With sperm competition relationships, there cannot be any certainty.
Especially in animals (like humans) where only a single ovum is up for grabs, the outcome of sperm competition is very important. Traditionally, males with more sperm have been considered favoured but other factors are now being given more consideration. Either way, the males with “winning” sperm types, whether that’s volume, speed or whatever, are more likely to pass on their genes, while the “losers” will not. This means, in a truly competitive sperm sexual system, there will almost certainly be a reduced genetic diversity of offspring.
That's one of each, one for males and one for reproduction.
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