Jeffrey C. Hall, Michael Rosbash and Michael W. Young are the joint winners of the 2017 Nobel Prize in physiology or medicine, winning for their discoveries about how internal clocks and biological rhythms govern human life.

The three Americans won "for their discoveries of molecular mechanisms controlling the circadian rhythm," the Nobel Foundation says.

From the Nobel Assembly at Karolinska Institutet, which announced the prize early Monday morning:

"Using fruit flies as a model organism, this year's Nobel laureates isolated a gene that controls the normal daily biological rhythm. They showed that this gene encodes a protein that accumulates in the cell during the night, and is then degraded during the day. Subsequently, they identified additional protein components of this machinery, exposing the mechanism governing the self-sustaining clockwork inside the cell. We now recognize that biological clocks function by the same principles in cells of other multicellular organisms, including humans.

"With exquisite precision, our inner clock adapts our physiology to the dramatically different phases of the day. The clock regulates critical functions such as behavior, hormone levels, sleep, body temperature and metabolism."

Hall, 72, was born in New York and has worked at institutions from the University of Washington to the California Institute of Technology. For decades, he was on the faculty at Brandeis University in Waltham, west of Boston; more recently, he has been associated with the University of Maine.

Rosbash, 73, was born in Kansas City, Mo., and studied at the Massachusetts Institute of Technology and at the University of Edinburgh in Scotland. Since 1974, he has been on faculty at Brandeis University in Waltham, Mass.

Young, 68, was born in Miami, Fla., and earned his doctoral degree at the University of Texas in Austin. He then worked as a postdoctoral fellow at Stanford University in Palo Alto before joining the faculty at the Rockefeller University in 1978.

Last year's winner was Japanese biologist Yoshinori Ohsumi of the Tokyo Institute of Technology, who was recognized "for his discoveries about "autophagy — a fundamental process cells use to degrade and recycle parts of themselves," as NPR's Rob Stein reported.

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