This year’s Nobel prize for Physiology or Medicine was given to three scientists for their work in understanding the nature of circadian rhythms, the daily pattern of life that we all, animals and plants alike, follow that seems to be governed by the rate of the Earth’s rotation about its axis. This topic has been of interest as far back as the 18th century when astronomer Jean Jacques d’Ortous de Mairan found that the leaves of mimosa plants opened at the time of daybreak and closed at night, even when they were kept in the dark all the time, suggesting that there was an internal biological clock that was not triggered entirely by sunlight.

The press release accompanying the award explained the origin of the term (“from the Latin words circa meaning “around” and dies meaning “day””) and what the scientists found about how it operates.

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.
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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. Our wellbeing is affected when there is a temporary mismatch between our external environment and this internal biological clock, for example when we travel across several time zones and experience “jet lag”. There are also indications that chronic misalignment between our lifestyle and the rhythm dictated by our inner timekeeper is associated with increased risk for various diseases.

The press release goes on to describe in more detail how the biological clock works but my attention was caught by this figure that illustrates how our body functioning varies through the day.

It answered a question that had come into my mind recently, now that winter is approaching and the nights are cold. I had noticed that although I was warm under the covers when I went to sleep, I would sometimes wake up around pre-dawn feeling cold and feel the need to pull the covers over me more closely to get warm again. I had wondered whether this was because that time was the coldest outside, so that in addition to the saying “It is always darkest before dawn” we could add “It is always coldest before dawn”. But while that might be true outside, since the house is heated to the same temperature throughout the night, that explanation did not make much sense. Now I realize that it is not the ambient temperature but my internal body temperature that drops round that time.

I always feel a sense of pleasure when science answers a question that has been puzzling me, even if it has no practical consequences.

I might as well use this as an excuse to post once again Sammy Davis Jr. singing Rhythm of Life in the 1969 film Sweet Charity, because in addition to being a great song, the wacky clothing styles from that era never fail to crack me up.