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Sperm and Egg Couplings May Be as Complex as Courtship in Humans

The fastest sperm wins the right to fertilize the egg. So goes the long-held interpretation of fertilization. In an October 2017 paper published in GENETICS, Joe Nadeau, PhD, a researcher at the Pacific Northwest Research Institute (PNRI), challenged that understanding, asserting that it may be more of a courtship dance than a competition.

The Role of “Chemistry” in Sperm-Egg Selection

“The thought was that fertilization was either simply a matter of being the first sperm to arrive at a passive egg, or if several sperm arrived at the same time, it was random,” says Joe. “But the combinations were strongly biased on the genetic content of both egg and sperm, suggesting they have some way of attracting, assessing, and choosing each other.”

In the past, scientists have noted in their own data that the sperm-egg combinations are not completely random, but they attributed it to other causes. Joe, an internationally recognized expert on mouse genetics, was not so eager to explain it away.

“We are usually very careful in choosing our partners,” he says. “Why shouldn’t a sperm and egg also be highly selective?”

If the egg and sperm have the ability to recognize fitness attributes in each other, it would change the way doctors determine the likelihood of a child inheriting a disease and could shine new light on evolution itself.

How Might an Egg and Sperm Sense Characteristics in Each Other?

“It may be as mysterious as the ‘chemistry’ we talk about when we choose partners,” says Joe. “Sperm and eggs may not have to worry about their physical attractiveness, their bank account, or what they wear, but they may pay attention to the quality of each other’s genetic content.”

Joe’s paper attracted a great deal of mainstream media attention in the U.S. — including in The Atlantic and Quanta — as well as in Europe, South America, and Asia.

It seems everyone loves a good love story.

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