Allan Rechtschaffen, a sleep researcher at the University of Chicago died on Nov. 29 at his home in Chicago. He was 93.

Dr. Rechtschaffen tested the effects of sleep deprivation, studied dreaming, narcolepsy, napping and insomnia, and standardized the measurement of sleep stages. REM and other aspects of sleep became the focus of his career. In 1958, he was named director of the university’s sleep research laboratory, where his experiments on animals and humans over the next 41 years helped him define a challenge that he described this way: “If sleep doesn’t serve an absolutely vital function, it is the biggest mistake evolution ever made.”

Even after his retirement in 2001, he continued to search for the reason people sleep. “The question of the function of sleep has not been solved,” he said. “We have a lot of leads about what the function of sleep might be. But we haven’t nailed it down. A third of our lives still remains for the most part a mystery.”