Higgins Professor of Biology Emeritus George Wald, the Nobel Prize recipient and peace activist hailed by Time Magazine as one of America's best teachers, died of natural causes Saturday, April 12 at his home in Cambridge. He was 90.

A member of the Harvard community since 1934, Wald was a pioneer in the study of how people see. His research on the biochemistry of vision earned him the 1967 Nobel Prize in Medicine or Physiology.

But according to family members, teaching meant as much to this man as research. For decades, he taught Natural Sciences 5, a first-year biology course that he invented. In a 1966 cover story, Time Magazine named Wald one of the "ten best teachers in the country."

In the classroom Wald was known for explaining seemingly complex scientific concepts with ease and never losing the bright and engaging sense of humor that also made him a popular and influential public speaker.

In 1969, Wald delivered a talk at MIT entitled "A Generation in Search of a Future" in which he openly opposed U.S. involvement in both the Vietnam War and in the arms race.

Reprinted and widely circulated, the speech brought Wald squarely into the political debate of the times. There was little resistance on his part--Wald took his thoughts on the Cold War, nuclear power, human rights and other issues to college campuses across the nation and to audiences around the globe.

Arrested on several occasions for his beliefs, Wald made special visits to Vietnam, China, Iran, Cuba, Nicaragua and the Soviet Union.

He served as the president of international tribunals investigating human rights abuses in several countries.

Family said Wald was proud to be included on former president Richard M. Nixon's "Enemies List."

Wald was born in Manhattan's lower East Side on Nov. 18, 1906, the youngest of three children.

His parents were Jewish immigrants who met while working in New York's garment trade. The family moved to a decayed section of Brooklyn, where Wald spent his youth.

Valedictorian and vice-president of his class in high school, Wald received his undergraduate degree from Washington Square College of New York University, the first college on the subway line from Brooklyn.

Wald did graduate work at Columbia University, then served as a National Research Council Fellow from 1932-33 in Berlin, where he began the research that would become the foundation for his later scientific endeavors.

Because of Hitler's activities, Wald was exiled to the U.S., landing in the Department of Physiology at the University of Chicago, where he remained until becoming a biochemical sciences tutor at Harvard in 1934.

Wald was named Associate Professor of Biology in 1944, and Professor in 1948.

He received the Higgins chair in 1968 and entered retirement 20 years later, devoting the rest of his life to studying questions of human consciousness; early Jewish and Christian history and theology; and unusual aspects of the life and teachings of Jesus Christ.

Wald was wed twice. In 1931 he married Frances Kingsley, with whom he had two children, Michael and David.

He married longtime co-worker Ruth Hubbard in 1958. The couple also had two children, Elijah and Deborah.

Wald is survived by nine grand-children and three great grandchildren.