A doctor has made a discovery that seems obvious but eluded scientists forcenturies, writes Dick Ahlstrom.
The human body regulates its temperature very strictly, normally varying only fractionally either side of 37 degrees. Why it does so may have as much to do with physics and mathematics as with biology.
Nature's selection of 37 degrees gave Prof Sidney Lowry of the oncology department at Waterford Regional Hospital pause to think. It also gave him an opportunity to return to aspects of the physics degree he completed at Queen's University Belfast before deciding to become a physician.
Early Earth was a place of extremes when water-based life began to evolve. There were high temperatures early on, but cooler conditions later took things down below freezing. Given that water boils at 100 degrees and freezes at zero degrees, logic would dictate that life forms dependent on it would have reached a midpoint of 50 degrees, yet this was not the case, says Lowry.
"When we moved from cold-blooded to warm-blooded animals, a range of temperatures emerged. The higher forms of life settled for 37. Life eventually settled on a very narrow temperature range close to this point." Elephants, for example, maintain a temperature of about 35, many birds one of about 41.
He paid little attention to it as a physicist but looked again after finishing his medical degree, also at Queen's. "It occurred to me quite early on that this was important," he says. His physics training allowed him to see it in a different light.
Scientists studying safer limits for radiotherapy used to base their work on the number of cells killed by a radiation dose, with 50 per cent - the logical midway point - initially selected as a benchmark. They learned very quickly, however, that cells did not die from radiation exposure in a way consistent with this benchmark. The death rate traced a mathematical concept, the exponential decay curve.
"The exponential decay curve is used in radiobiology research. It is used to study radiation damage in cells," says Lowry. The midway point on the exponential decay curve is actually 37 per cent, not 50 per cent, causing radiobiologists to modify their benchmark.
The same curve applies in the half-life decay of radioactive materials, says Lowry, as it does when studying the decay of foam bubbles on a head of beer. Boiling water also follows this exponential decay curve when it cools, losing heat quickly at first but then slowing. Water's midpoint was predicted by the law of cooling, the exponential decay curve proposed by Isaac Newton 300 years ago.
It struck Lowry that the 37 degree midpoint for the cooling curve of water was the very temperature adopted by the human body for its internal thermostat. This fundamental principle of human physiology had apparently lain undetected for centuries until his observation, which was published in a recent issue of the leading medical journal the Lancet.
That nobody seemed to have connected the two was the most extraordinary aspect, says Lowry. Nobody had pinpointed why 37 degrees, rather than any other temperature, ideally suited life.
The link between the two seems more than simple chance. Body temperature varies through the day, higher during daylight, lower at night, with an average of about 36.65 degrees, says Lowry. If you trace the exponential decay curve for cooling water, the precise midway point actually lies at this figure, not at 37 degrees. "It comes out to exactly 36.65," states Lowry. "I find that remarkable."