I was supposed to go to the Australasian Sleep Association conference this week. Actually, I was planning to attend a single day on non-respiratory sleep disorders, and then come home.
So I gave myself two days to get to Christchurch and attend the meeting and get back again.
However, at the end of a pressured and busy day on Monday I decided to pull out, and stay home.
What a great decision! Two days of no consulting in Hamilton, where the sky is blue and the temperature in the low 20s. And where there are no earthquakes!
I’m taking today as a PD day, and spending some time with the new sleep medicine multimedia text. I’ve just been looking at some stuff on chronobiology – that is, day and night rhythms.
These rhythms seem to be built into every living thing. The section of the textbook begins with an evaluation of the historical recognition of day night cycles. They start with Alexander the Great, who observed and recorded daily leaf and flower movements around about 400 years BC, and then skipped well into the enlightenment period, a span of over 2000 years, to 1729. In that year it was demonstrated by a chap called Jean Jacques d’Ortous de Mairan that leafs opened in a circadian (day/night) rhythm that was independent of the environment of the leaf. Even in a dark closet the plants leaves closed up at night time, opening in the morning in anticipation of sunlight! (This video from youtube demonstrates the behaviour of beans - exposed to sunlight, with thanks to mrlutzvulturepeak).
Daily changes in the body temperature of people were demonstrated in 1866 by William Ogle. Charles Darwin suggested in 1880 that periodicity of leaf movements was a feature of all plants. In the 20th century various insects and animals, and people, have been demonstrated to have circadian rhythms which are independent of external stimuli. In the case of people, if we are not exposed to the modifying impact of sunlight we demonstrate a circadian rhythm which runs over about 25 hours. That is, if a person lives in a cave (as a chap called Michel Siffre did, for example, for 2 months in 1962 – an ice cavern no less) then our biological rhythm gets out of sync with the outside world to the tune of about one hour every day.
Here’s the thing – I quite like reading history. And I read a lot of the Bible. In particular at the moment I’m memorizing the first chapter of the book of Genesis for something that I want to do with the kids at our church in a couple of weeks.
So if we want to think about when humans first recognized day-night rhythms that impacted on plant life then think we should think about this, for example:
“Then God said, let there be lights in the expanse of the heavens, to separate the day from the night. And let them be for signs and for seasons, and for days and years, and let them be lights in the expanse of the heavens to give light upon the earth. And it was so. And God made the two great lights – the greater light to rule the day and the lesser light to rule the night – and the stars. ……And God saw that it was good. And there was evening, and there was morning, the fourth day.”
No one knows for sure when the book of Genesis came to be written. It was probably written around the 5th century BC. The stories contained within it were probably well established in oral tradition by then Even if you don’t believe that these stories constitute sacred scripture, at the very least they are very old, and culturally very important, stories.
One of the striking things for those of us interested in day and night rhythms is the constant refrain within these very-old stories, which follows after every creative exertion of God. “There was evening, and there was morning, the first (second, third…..) day.”
The pervasiveness of chronobiological, and in this case particularly day/night or circadian rhythms, in animal and plant life, even when those animals or plants are born and raised without the influence of external factors (like the sun, and variable temperature), is startling, and not satisfactorily explained by science. It seems to me that this is just the way everything is made.
Andrew
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