Biology

Thanks to the feedback loop principles inherent in quantum physics, the complex molecules that are the building blocks of life are allowed to form. But life might not get very far in terms of longevity or complexity if the principle of feedback loops didn’t carry right on through from the realm of physics to that of biology.

One of the best ways to understand how feedback loops sustain and encourage the evolution of biological forms is to begin with a deceptively simple case that isn’t an example of organic life at all, but a simulation designed by James Lovelock and Andrew Watson called "Daisyworld".

Daisyworld is a planet that consists exclusively of white and black daisies. Black daisies are exceptionally efficient at absorbing light for use in photosynthesis. White daisies are useful for reflecting light so that areas on the planet don’t get too overheated. Both populations of daisies share the resources of the one planet, and thus they are engaged in a feedback loop. That is, as one species is successful, the other must decline, or while one species begins to disappear, the door is open for the other to take its place. The heat energy bathing the planet (from a hypothetical sun) is held constant.

When the simulation is run, the populations of white and black daisies fluctuate for some time before settling into a kind of equilibrium. But while all of that is being negotiated, so to speak, the temperature of the planet also fluctuates. While without the daisies the planet would sit at a constant 50 degrees, say, it might hit 80 degrees when the black daisies dominate (since they absorb and hold heat energy), or it might drop to 30 degrees when the white daisies dominate (because they deflect heat energy back into space). As equilibrium is attained, a steady temperature level optimal for daisy growth emerges from the feedback loop. In fact, if the "sun" is programmed to steadily increase its heat output, the daisy populations will fluctuate in whatever ways necessary in order to maintain that ideal temperature in spite of the increase. The ideal temperature can hold for some time before the increase is so great that it overwhelms the system.

This isn’t a perfect model of how the Earth works, but it demonstrates well how intuitive the feedback loop principle really is. As organisms engage in the symbiotic relationships that define life on this planet, certain spontaneous, self-organizing phenomena (like the maintenance of optimal temperature) are bound to occur.

Evolution of species toward greater adaptability is the best example of how such phenomena emerge out of the feedback loops of ecosystems. In the course of its history, an entire species can go through a number of changes as its members respond to various ecological conditions. Part of the group may change migratory habits in response to adverse climate conditions. Weaker members of the group will be culled by predators. Individuals who can eat and digest a new and more plentiful foodstuff may live longer and produce more offspring. A competing species might be wiped out by disease. A natural disaster may destroy half the population, but that means there is enough food to go around during the winter. Over time, if the species continues to survive, a more robust species is the result, as if all the trials it endured were designed to make it better and stronger. But all of that apparent progress was just the result of the species spending time in the feedback loop that connected it to all the other species in the ecosystem.

I tell you what, that Grandpappy of mine sure knew what he was doing when He slapped it all together, didn’t he?

Of course, He wasn’t finished with feedback loops. Because for all of that work what Grandpappy REALLY wanted was someone else to talk to.