In the 1980s, when marriage and adopting children seemed impossible dreams for gay men, the psychoanalyst Richard C. Friedman became their champion.

His 1988 book, “Male Homosexuality: A Contemporary Psychoanalytic Perspective,” showed that sexual orientation was largely biological and presented a case that helped undermine the belief held by most Freudian analysts at the time that homosexuality was a pathology that could somehow be cured.

“I felt an ethical obligation to find the reasons for anti-homosexual prejudice,” he once told an interviewer. His wife, Susan Matorin, a clinical social worker at the Weill Medical College of Cornell, put it more plainly: “Straight people had the same personality issues, and they got away with murder, but gay people were stigmatized, and he didn’t think that was right.”

Friedman’s motivation wasn’t political. “He very much felt like you followed the science, and it didn’t matter what the political backdrop was,” his son, Jeremiah, a screenwriter in Los Angeles, said in a phone interview.

Although the American Psychiatric Association, the dominant mental health organization in the United States, changed its diagnostic manual in 1973 and stopped classifying homosexuality as an illness, psychoanalysts continued to describe homosexuality as a perversion, and many believed it could be cured.

Friedman, using studies of identical twins and theories of developmental psychology, made a scholarly rather than ideological case that biology rather than upbringing played a significant role in sexual orientation.

It was a direct challenge to popular Freudian theories and thrust him into the center of debates among the more established heavyweights of psychoanalysis. It led to a model in which analyst and patient simply assumed that homosexuality was intrinsic, said Jack Drescher, a professor of psychiatry at Columbia University who knew Friedman and would later offer his own critiques of Friedman’s theory as new approaches to working with gay and lesbian patients emerged.

“Given that he was a younger colleague, it was brave of him to take older experts on,” Drescher said. But it was in keeping with who he was. “He had an edge and wasn’t afraid of anybody,” he said.

Friedman died on March 31 at his home in Manhattan. Though the specific cause was not clear, Matorin said, he had for years been grappling with a number of health problems, including cardiac and metabolic conditions. He was 79.

Richard C. Friedman was born on Jan. 20, 1941, in the Bronx, the oldest of three sons of William Friedman and Henrietta Fuerstein. His father was a food inspector for the city; his mother a teacher.

His parents instilled in their sons a deep love of learning — all three would go on to become doctors — and of music, insisting on violin and piano lessons. Friedman would help pay for medical school by playing the accordion at events, and he remained an excellent pianist.

At the time, a child could still get beaten on the streets of the Bronx for being, like Richard, Jewish, and his family was deeply affected by genocide in Europe during World War II.

While he was at the Bronx High School of Science, he received a National Merit Scholarship and used it to attend Bard College in Annandale-on-Hudson, New York, graduating in 1961. Five years later he graduated from the University of Rochester School of Medicine and Dentistry and became a psychiatric resident at the New York State Psychiatric Institute and the Columbia Presbyterian Medical Center, both in Manhattan.

Although he was best known for his work on human sexuality, Friedman was equally proud of a study he did at the medical center that showed that medical interns performed poorly when they were sleep-deprived. The work helped change how medical schools trained up-and-coming doctors.

After enlisting in the United States Army Medical Corps, he became chief of inpatient psychiatry at William Beaumont Army Medical Center in El Paso, Texas, where he treated traumatized young men returning from the Vietnam War. It was there, his son said, that his suspicion of ingrained authority deepened.

Friedman would go on to become a clinical professor of psychiatry at Weill Cornell Medical College and a faculty member at Columbia University. He published more books and numerous articles on human sexuality, working with Dr. Jennifer Downey, a Manhattan psychiatrist and Columbia professor. He was also the longtime editor of the journal Psychodynamic Psychiatry.

Intellectually restless, Friedman was a civic-minded student of history who was well-versed in Shakespeare, a devoted reader of biographies and a fan of opera, not to mention the New York Knicks.

He was also a methodical man with distinct tastes, his family said. He always carried a copy of the U.S. Constitution, and without fail he would slip on gaberdine pants, an oxford shirt, a tie and a blue blazer when he went to his office on Manhattan’s Upper West Side. Saturdays were more casual. He left off the tie.

In addition to his wife and son, he is survived by two daughters from a previous marriage, Heidi Friedman and Carla Greene; two brothers, Daniel and Joseph; and two granddaughters.

Although his critics found him to be unyielding in his views, coming off as if he thought he was the smartest person in the room (and often he was), he had a thriving private practice and devoted patients.

One was the author Andrew Solomon, whose book “The Noonday Demon: An Atlas of Depression” won the National Book Award for nonfiction in 2001. He was Friedman’s patient for 25 years. Without him, Solomon said, he might never have understood that as a gay man he could be married and have a family, or that he was capable of professional accomplishment.

“What was most striking was just his confidence and clarity,” Solomon said.

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