Having taken time off from books yesterday, spending much of the day potting up tomato, pepper and aubergine plants, and fuchsia cuttings, I was in need of some cerebral stimulation, and so in the early evening I was on the train to London with my youngest daughter, going to a Friday Evening Discourse at the Royal Institution. It’s traditional to dress up for these – the Ri website points out “FEDs are by tradition formal occasions, and while evening dress is not obligatory, it is customary”. So I was feeling a little uncomfortable in my stiff shirt, only donning the bow tie when I got there. To get me to wear a tie of any description is quite an accomplishment, (weddings etc excepted) it only happens for a FED. They are consistently interesting and they are usually given by scientists at the top of their field – Roger Penrose and Steve Jones are two of the better-known who have appeared recently, but they are always of that calibre.
The discourse this month was Seasons of Life: The biological rhythms that enable living things to survive and thrive, by Russell Foster (Professor of Molecular Neuroscience at Imperial College, London, and a leading international authority on circadian rhythms). As is often the case, there’s a book of the same name, which was published last year (ISBN 9781861979148), Leon Kreitzman is co-author.
The talk was fascinating, starting off by explaining why there are seasons (apparently 90% of US graduates get this wrong), and then discussing the effects of the seasons on animal life, on their breeding cycles, on migration, and on hibernation. I imagine that my 13-year-old daughter now knows more about hamsters’ and sheep’s reproductive organs than any of her peers.
It’s fascinating how scientists have recently unpicked the mechanism in the eye, then the brain, and then the other physiological reactions which produce the circannual breeding cycle in animals. His examples here were hamsters and sheep (male hamsters’ paired testes weigh 0.2g in the non-breeding state, but 5g when reproductively active – in humans think two 10-pin bowling balls). The trigger for changes is photoperiodicity, i.e. changing length of daylight, and depending on the animal it can be either shortening or lengthening lengths of daylight. And the actual physiological mechanism is a convoluted series of chemical reactions.
But some mechanisms must involve an internal clock, as hibernating animals know when to wake even though they may be in total darkness. The site of the endogenous circadian (24-hour) clock in the brain is known – it’s been identified when the relevant area of the brain has been damaged – but the mechanism of the endogenous circannual clock is still a total mystery.
What was most fascinating to me is how seasonal humans are. Humans get diseases seasonally, suicide rates alter seasonally, and, strangest of all, the month you are born in affects the probability of your contracting certain diseases, both physical and psychological. The studies which show this have a useful control – there are mirror images in the southern hemisphere.
The mechanism isn’t really understood in humans, but photoperiodicity is thought to be the trigger. There’s no proof, but an interesting study in Spain has shown there was a distinct seasonality in birth-rates which practically disappeared in the nineteen sixties. Until this time the population of Spain was essentially rural, but after massive and rapid industrialization the majority of the population moved to an urban, indoor factory life, away from natural light.
There wasn’t long at the end for questions, I didn’t have time to ask about about the seasonal cicada, which emerge together over a 13 or 17 year cycle. How does that work? 13 and 17 are both prime numbers, which is thought to help them avoid predators.
I haven’t read the book yet, there’s too much else at present, but it’s sitting quite high on my pile of future reading.
And then off post-haste to meet my eldest daughter at Victoria Station. She has just finished her exams and has come down from university for a long weekend.