A professor investigating the question of why sex exists has been awarded a medal for lifetime contribution to genetics.

Matthew S. Meselson, Cabot professor of the natural sciences, has won the annual Thomas Hunt Morgan medal of the Genetics Society of America and will be featured in next month's issue of Genetics.

"I was surprised," Meselson said, upon receiving the letter informing him that he had been chosen for the prize. "It feels very nice. The other people who have received this award are people I have admired very much and it is nice to be closer to their tradition."

Meselson, a famed Harvard biologist, is currently researching asexual reproduction and the reason for the existence of sex.

"There is no general agreement why sex exists," he said. "It's a big mystery."

Meselson is studying a species of microscopic all-female pond dwellers called the bdellois rotifers. The rotifers live without sex and have no males, sperm or fertilization among their species.

Since rotifers reproduce asexually, a daughter should inherit all her mother's genes.

But after studying the rotifers, Meselson developed the idea of a silent mutation, a change in genes that has no effect on an organism.

Meselson examined the genes of the rotifers and found that their alleles showed differences about 300 times as often as those of another species of rotifers that are known to reproduce sexually.

While most scientists believe that sex is essential to evolution, Meselson's findings cast doubt on that assumption.

He wonders why, if the bdelloids have been able to evolve asexually for millions of years into hundreds of species, other species can't do the same.

"Why is it that almost all other species, both plant and animal, reproduce sexually," Meselson asks. "There must be a big advantage for them, but not for rotifers."

Meselson's study of the rotifers is demonstrated in a cartoon in Science Classics by Larry Gonick, a professor at MIT.

Meselson received the Hunt Medal for his lifetime of contributions to genetics.

Meselson studied questions of how DNA chains replicate and found that the chains come apart and each makes a new partner. His studies with Frank Stahl on replication led to the Meselson-Stahl model of DNA recombination, now a fixture in genetics textbooks.

He examined the process of recombination, looking into how two different DNA chains from different parents produce a DNA molecule which has parts of one and parts of the other.

He has also explored how DNA molecules correct errors in their replication, and how they carry out the process of restriction, when a cell recognizes and wants to destroy a foreign DNA model that enters the cell.

Finally, Meselson has examined the idea of suppression, or how mutations can be compensated for each other.

Meselson, a graduate of the University of Chicago, first came to Harvard in 1961. Starting as an associate professor, he was promoted to Cabot professor in 1976. He served as chair of the Department of Biochemistry and Molecular Biology from 1976 to 1979.

Meselson has also done work in public policy, applying the problems of science to warfare and international security. His work earned him a place on the notorious Nixon "enemies" list, along with then-Harvard president Derek C. Bok.