4.8 Biological clocks.
When two or more non-linear oscillators interact by coupling, the phenomenon of sub-harmonic resonance (or frequency division) may occur. In this way a periodicity of great regularity can be obtained that has a larger amplitude than that of the primary oscillators. Circadian clock mechanisms of many different species of organism are "synthesized" from oscillations with a period considerably less than 24 hours. In Goodwin's experiments fluctuations with periods of 1-4 hrs were measured in concentrations of a radioactive labelled amino-acid in chick embryo's. Large populations of cells remain in synchrony with each other, even a whole group of embryo's is in synchrony. Such findings help to understand the temporal organisation in the developing embryo.
A cell is a living system and is composed of many interacting non-linear oscillators. These act as if they were themselves evolving populations. We also encounter evolving populations of oscillators in multicellular systems:
in an ecosystem numerous plant- and animal species adapt to a new challenging environment, and in turn adapt the environment to their needs. The varying rate of increase and decline of a species results in oscillation which is firmly coupled to (periodically) changing circumstances
in an animal's immune system globulin producing cells are stimulated to multiply by infecting agents, and inhibited by other agents; the oscillating 'species' of immune globulins interact and form a network
in a central nervous system groups of neurons (quasi 'species') interact in a brain area when they adjust to a learning task (Edelman 1987).
Development in these systems is engendered by the Darwinian principles of competition and selection. What exactly will be selected may be undecided. It is probably not one particular 'species' (or one or more of it's features), because it's fate is too closely coupled to it's immediate environment to be distinguished from it. We are tempted to believe that the target of selection is an oscillatory pattern that promotes resiliency within the system and so has survival value. Under the influence of random disturbances a population of interacting oscillators will evolve from states of less to states of greater complexity. The selecting principle works for maximum adaptive value. Evolution is always creative and innovative
We have had a look through our tele-microscope at various windows in the evolutionary process, without having to strain our powers of imagination. By adopting the habit of switching between adjacent windows, we have seen similarities that would otherwise have escaped our notice. Oscillations, coupling, and layered networks are not metaphors, created by an imaginative mind, they actually exist. Since Goodwin has demonstrated them in his chicken embryo experiments other researchers have given evidence, as a perusal of a review volume by Gray and Scott (1990) will show. The fact that more than a few students will have difficulty in understanding the reports, should not be a reason to mistrust the validity of the concept of coupled oscillations. It should rather be an exhortation to look for more examples in one's own area of expertise e.g.
well-timed administration of drugs increases their efficacy and diminishes unwanted side-effects
social developments have been greatly influenced by coincidences that occurred at a particular phase of oscillation
changes on the earth's surface and in the earth's atmosphere caused by human activity may have different effects on the climate, depending on the phase of climatic rhythm through which our planet is passing at the time.
The importance of temporal dynamics lies not only in the number of practical applications, but even more in the conceptual homogeneity of theoretical approaches in various disciplines.
Seeds of cultural information can lie dormant for a long time before being rediscovered