#2 - The Law of Negative Feedback

 (This is the third of a nine-part installment, offering a fresh new perspective on Climate Change.  For the big picture summary, see Turning Climate Change on its Head.)

Exponential growth and non-stop resource depletion are entirely unsustainable on a finite planet.  Nature controls for these imperatives by providing negative feedback mechanisms.  Evolution balances these two forces.  However, if the negative feedback is too great, the species will disappear.  On the other hand, the negative feedback can’t fail, because if it did, the unsustainability of exponential growth will be its own demise - it’s the ultimate negative feedback.

Evidence of hare and lynx population cycles

In part 2 (The Law of Propagation and Consumption), we established that, in the absence of counter-balancing forces, every living species would theoretically experience exponential growth.  The reality is that this does not happen in nature.  Populations grow and decline, often in somewhat predictable cycles.  Sometimes a population will decline to the point where a species will go extinct, but it has never been the case that a population's growth has continued unchecked to the point where it is occupying every square inch of the planet, crowding out every other living thing. 

Evolution is a remarkable, self-regulating process, operating in an environment of interconnected systems, whose complexity far exceeds our capacity to fully understand it.  One of the key attributes that evolution has created is a system of negative feedbacks that provide the counter-balancing force to population growth, referred to above.  If we can accept that no species is programmed to control its own population numbers, then this proves that something is controlling that exponential growth.  (Even if a species could be shown to be controlling its own numbers, would that not be evidence of nature giving them negative feedback that they were reacting to?)

We can demonstrate the presence of negative feedback by examining the three possible outcomes of a species population growth:

(a)  Extinction

The population declines permanently to zero.  As mentioned above, this would be evidence of negative feedback going too far, driving a species to extinction.  You may wonder why this does not happen very often.  (In the natural world, with no human interference, the extinction rate is estimated to be between 0.1 and 1 per million species per year).  The explanation is that nature's systems and cycles have been adjusting and fine-tuning themselves over millennia.  In the absence of rare, catastrophic events (e.g. a meteor impact), if the systems did not support the eventual restoration of any given species population, that species would have already disappeared a long time ago.

(b)  Steady population or cycle

Maintaining any living organisms (be they animal, plant, or microscopic) at a precise and constant population number would require a direct oversight that would be out of place in our natural world.  It is easier to accept that biology's intrinsic system designs merely react to the numbers going up or down in such a way that balance is eventually restored.

In the image shown at top, evidence of lynx and snowshoe hare populations in Canada's North over nearly a century was derived from the fur trading logbooks of the Hudson's Bay Company.  What we see is that as hare populations increased, the lynx numbers soon followed.  This is because the snowshoe hare is a common food for the lynx; a greater number of hares mean that a greater number of lynx remain healthy and survive the winter.  Following its own innate propagation programming, more lynx also means more having offspring that will also be feeding on the hares.  Eventually, the hare numbers begin to go down as they are eaten by the growing lynx population.  As soon as the hare numbers drop, so do the lynx numbers, as their food source disappears.  Of course, the lynx/hare pairing is not an isolated system.  Hare populations will also go up and down in relation to their own food sources and how many hares have to compete for that sustenance.

Limited food supply, which becomes scarcer as the consuming population rises, is one of the most common examples of nature's negative feedback mechanisms.  Another is susceptibility to disease due to increased population density.  Note how both mechanisms intrinsically become more effective as the population numbers increase - that's how negative feedback works.

(c)  Uncontrolled growth

All life, as we know it, requires energy consumption and habitat space.  If we presume it possible for any given species to increase in number without end, then the available energy and space would also have to be unlimited.  Neither is true on this finite planet.  Therefore, even if you could imagine a species that was able to circumvent every possible negative feedback mechanism thrown at it by nature (i.e unlimited food supplies, no increased susceptibility to disease, unlimited energy, etc.), that population would sooner or later hit the natural limits of energy and space on a finite planet.  In this case, you could think of those limits as being the ultimate negative feedback.

Astute readers will notice that humans seem very close to being examples of this third possible outcome.  They have adapted to life on every possible environment of the planet, managed their own food sources, cured diseases and increased life expectancies, found new energy sources, and (some might say) are even poised to colonize other planets.  I consider this an illusion, and we'll discuss this next in part 4 (The Myth of Self-Control and Immunity).

Conclusion

Looking at the three possible outcomes, I suggest that, from the collective perspective of any given species, the most desirable outcome is the second one, where nature uses negative feedback to manage the innate growth of their population to levels which can be sustained for many, many generations, evolving as time and other factors permit.  In other words, if we accept the first Law of Propagation and Consumption, then negative feedback is necessary for sustainable species existence.

(Continue to part 4 of 9)