Thomas Dudley Cabot Professor of the Natural Sciences Matthew S. Meselson has devoted his career to studying questions in molecular biology and fighting biological warfare.

His current research focuses on the mechanisms of molecular evolution, or more simply, why there are two sexes.

Meselson is now researching whether species can proliferate and survive without sexual reproduction.

Of the two million species of plants and animals alive today that have been named, 2,000 are purely female and reproduce asexually, Meselson says.

However, these species appear to become extinct every few thousand years. But entirely new asexual species then appear, Meselson says.

The prevalence of sexual reproduction in 99.9 percent of known species indicates that there must be some type of strong selection for it, he says.

However, scientists are unsure what the exact biological basis for sexual reproduction is.

"It is a very deep, fundamental and ancient question in biology," Meselson says.

Meselson is currently trying to unravel that mystery.

One way to study the question, Meselson says, is to determine whether a species has managed to proliferate despite remaining asexual.

Bdelloid rotifers-asexual organisms that are believed to have survived millions of years-are the focus of Meselson's studies.

These freshwater invertebrates, comprising more than 350 species, are believed to reproduce without sex. Meselson's group studies these organisms to determine whether sexual reproduction is even necessary.

Such a study is a complicated and manifold process.

Scientists must first ensure that bdelloid rotifers are and always have been asexual.

Meselson is using DNA sequence analysis and chromosome mapping to confirm the absence of sexual reproduction in their evolution.

"If that holds up," Meselson says, "we will test the molecular hypotheses for why sex exists."

Outside of the biology laboratories of Sherman Fairchild, Meselson serves as the faculty chair of chemical and biological studies at the Kennedy School of Government's Center for Science and International Affairs. He is also on its Board of Directors.

In this position, Meselson studies the uses and effects of biological warfare.

Meselson says biotechnology is the next big form of technology that will be exploited.

Modern science enables people to manipulate all life processes, including thought and heredity, he says.

If biotechnology is exploited, Meselson says, "it might be quite different from other weapons."

For example, one lone virus particle can cause as much damage as large quantities of explosives, Meselson says.

Biological warfare thus poses an unstabilizing threat which can only be prevented if nations agree to make the development and stockpiling of biological weapons a universal crime, he says.

Today, treaties simply prohibit nations from using such warfare, Meselson says. But he advocates harsher measures so that nations may indict and try individuals responsible for biological warfare.

"I think the world should move towards holding individuals responsible," he says.

This is the goal of the Harvard Sussex Program on Chemical and Biological Warfare Armament and Arms Limitation-a joint venture between Harvard and the University of Sussex in Britain-of which Meselson is co-director.

The group has written a treaty which makes the development and stockpiling of biological weapons an "international crime [so that] no matter where a person flees he can be found responsible and imprisoned." Meselson says.

The group is preparing to have heads of state introduce the treaty at the United Nations.

Meselson says his interest in science began at an early age.

He received a Ph.D. in physical chemistry from the California Institute of Technology in 1957 and served as a research fellow, an assistant professor of chemistry and a senior research fellow in chemical biology there in successive years.

In 1960, Meselson moved 3,000 miles across the nation to begin his career at Harvard as an associate professor of molecular biology.

He later served as a professor of biology for 12 years and has held his current title since 1976.

During his 37 years at Harvard, Meselson has taught a number of courses.

Meselson says that he believes the best way to master a subject is to teach it.

But with all of his activities, Meselson does not have much spare time.

However, when he finds the time, Meselson said he enjoys retreating to his family farmhouse in Woods Hole, Mass. where he grows eggplants and tomatoes.