Flavours of Synchrony in the Natural World

This was the title of the Dept. of Atomic Energy sponsored Raja Ramanna Prize lecture that was given at JNCASR yesterday. The speaker was Ramakrishna Ramaswamy – known better as ‘RamRam’ – from the School of Physical Sciences at JNU, New Delhi. The talk was quite broad and aimed at a general audience (unlike the other talk which was completely unintelligible to anybody who wasn’t a condensed matter physicist.)

The first observation of synchrony in the natural sciences was by Christiaan Huygens (ask me how that name is pronounced; it isn’t what you think) who observed that pendulum clocks that happened to be attached to a common beam started oscillating out of phase with each other. The modern day version of this effect can be seen in a popular YouTube video that uses metronomes that synchronise over a fairly short period of time. A summary of Huygens’ discoveries, then, is that weakly coupled systems oscillate in ‘sympathy’.

This effect is also fairly well studied in the biological sciences, RamRam pointed out. The Moran effect (1953, P.A.P. Moran) is the synchrony observed in populations of animals that have no physical contact with each other except that they inhabit islands close to each other. This effect has since been seen and studied in feral pigs, red squirrels and the magnificent synchronous flashing of fireflies in Malaysia, and several other animal populations, and even in neurons in the human brain. These systems are all in some sense ‘linear’, and have ‘weak coupling’. What happens if the coupling isn’t weak? Or if the systems are nonlinear? How about if the systems are chaotic? Or all the above? That is RamRam’s work.

This synchrony in nonlinear systems occurs in various types – Master-Slave, Mutual coupling, Common Master, and various combinations thereof. The synchronisation can also be complete, phase-only, with or without a time-lag, or generalised synchrony. The last one is the most common type observed in actual systems, and is also (therefore) the most mathematically involved.

What I want to say something about is a particular effect in humans that wasn’t talked about, but which is an example of biological synchronisation. It’s called the McClintock effect, and it is the synchronisation of menstrual cycles in cohabiting women. I read recently about an interesting variation of the McClintock effect. I should mention that the effect itself is by and large conjectural at this point (my prof says she’s seen this effect; her data aren’t rigorous or anything, though), so the variation of the (conjectural) effect may just be an exercise in speculation. At least it’ll be witty speculation, so it’s all right!

It turns out that heterosexually active women exhibit this effect more often than homosexual women, in whom this effect is very rarely seen. The SciAm article I’ve mentioned says that researchers at NYSU concluded that this was because of something about contact with semen. The obvious risque humour aside, it’s fascinating that the absence of synchrony in an organism when there is no reason to expect synchrony in the first place led to the discovery of some unknown facts about pheromones and their effects.

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