Naked Mole Rats are all teeth and skin. They are fairly ugly by our usual standards and as it turns out, so is their sperm, which is described as deformed and also sluggish. But that’s okay; they don’t need to move quickly or be good-looking since they don’t have much competition.
No sperm competition, that is. Naked mole rats live in colonies where their queen calls the shots. The queen chooses only one male at a time to mate with and suppresses the reproductive instincts of the other males in her world. This means that the chosen male’s sperm doesn’t have to outrun any other sperm. They can take their time on their way to the egg. There is no one else to race.
These findings come from Liana Maree of the University of the Western Cape in Bellville, South Africa, who recently studied the sperm of Naked Mole Rats and found that they may have the slowest sperm of any known mammal. According to her findings, only 7 percent of the sperm moved at all and those that did swim were clocked at 35 micrometers a second.
It appears that the more promiscuous the animal, the faster the sperm. Eliminate competition and sperm get slower.