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Primate sperm: speed matters

Jaclyn Nascimento, a Ph.D. candidate at the Jacobs School, used a specially equipped microscope to measure the swimming force and speed of primate sperm cells.
Jaclyn Nascimento, a Ph.D. candidate at the Jacobs School, used a specially equipped microscope to measure the swimming force and speed of primate sperm cells.

In a paper published in the Journal of the Royal Society Interface, a team led by Michael Berns, an adjunct professor of bioengineering at UCSD and a professor of biomedical engineering at the Beckman Laser Institute at UC Irvine, and UCSD Ph.D. candidate Jaclyn Nascimento reported that sperm cells from polygamous chimpanzee and rhesus macaque swim much faster and with much greater force that those of humans and gorillas, species where individual females mate primarily with only one male during a reproductive cycle.

"Rapidly swimming sperm cells would be evolutionarily favored in polygamous species and that is consistent with our measurements of chimp and rhesus macaque sperm," says Nascimento.

Nascimento found significantly lower swimming forces and slower swimming speeds with human sperm. Gorilla sperm was the slowest. "Dominant silverbacks are known to effectively discourage other males from mating with the females in their harems, so faster sperm wouldn't seem to be an advantage to them," Nascimento says. However, she and Berns were surprised that the speed and force of human sperm fell in between the gorillas and the chimps. "Maybe humans haven't always been as monogamous as we had thought," Berns says.

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