Zhores Medvedev, dissident Soviet scientist, at age 93

Zhores Medvedev, a scientist and one of the most prominent political dissidents in the former Soviet Union, whose writings exposed quackery and fraud in Soviet scientific programs and led to his arrest and eventual exile from his homeland, died Thursday in London. He died one day after his 93rd birthday.

His death was confirmed to Radio Free Europe by a friend, writer Semyon Reznik. Dr. Medvedev’s twin brother and fellow dissident, historian Roy Medvedev, told Russian news agencies that his brother had a heart attack.

Dr. Medvedev worked at leading Soviet laboratories early in his career and published nearly 100 research papers before his political activism derailed his scientific career. With expertise in microbiology, biochemistry and genetics, he grew particularly alarmed at the ideas propagated since the 1930s by Trofim Lysenko, a scientific charlatan who captivated the imagination of Soviet leader Joseph Stalin.

Lysenko, who denied the existence of genes, believed that plants and animals could be magically transformed or “educated” by force of will and exposure to Soviet ideals. Among other things, he said wheat plants could be changed to rye and that seeds soaked in freezing water could adapt to cold climates. Orange trees, he predicted, would one day grow in Siberia.

When these notions were put into practice, they inevitably led to disaster: rotting crops, soil depleted of nutrients and, ultimately, widespread famine. Nevertheless, Lysenko held sway over Soviet agricultural practices for years, and his influence could still be felt until Nikita Khrushchev was ousted as the country’s leader in 1964.

By then, Dr. Medvedev had been at work for three years in writing a history of Lysenko and his harmful doctrines. He worked with other scientists, including physicist Andrei Sakharov — who later received the Nobel Peace Prize — to expose Lysenko as a fraud.

Dr. Medvedev’s study of Lysenko was not approved for official publication in the Soviet Union, but samizdat, or clandestine, copies circulated among the intelligentsia. In 1969, the book was translated into English and published as “The Rise and Fall of T.D. Lysenko.”

Dr. Medvedev was fired from his job at an agricultural research laboratory, and within a few months was summoned to a meeting with a psychiatrist, on the pretext of discussing the behavior of his teenage son.

Instead, Dr. Medvedev was taken to a holding cell, where he managed to pick the lock and walk away.