Are mass extinctions inevitable?

It is well known from the fossil record that there have been a large number of extinction events of various magnitudes.  Some famous examples include the Cretaceous-Tertiary extinction that killed off the dinosaurs 65 million years ago and the Great Dying 250 million years ago where almost everything died.  It has been postulated that mass extinctions occur every ~30 or ~60 million years.  Most explanations for these events are exogenous – some external astrophysical or geological cataclysm like an asteroid slamming into the Yucatan 65 million years ago or large scale volcanic eruptions.  However, as I watch the news every night, I’m beginning to wonder if life itself is unstable and prone to wild fluctuations.  We are currently in the midst of a mass extinction and it is being caused by us.  However, we are not separate from the ecosystem so in effect, the system is causing it’s own extinction.

I listen to a number of podcasts of science radio shows (e.g. CBC’s Quirks and Quarks, ABC’s The Science Show, BBC’s The Naked Scientists, …) on my long drive home from work each day.  Each week I hear stories and interviews of scientists finding that climate change is worse than they predicted and we’re nearing a point of no return.  (Acidification of the oceans is what scares me the most.)  However, in all of these shows there is always an optimistic undertone that implores us do something about this, under the assumption that we have a choice in what we do.   It is at this point that I can’t help but to smirk because we really don’t have a choice. We’re just a big dynamical (probably stochastic) system that is plunging along.  We may have the capability to experience and witness what is happening (a mystery of which I actually have the privilege to think about for a living) but we don’t have control per se as I wrote about recently.

My question is whether or not the ecosystem is itself inherently unstable.  In the brain, the cortex has spontaneous “up and down” states where the neurons alternate between being mostly active and mostly inactive.  There have been several proposed mechanisms and none involve some exogenous agent.  It almost goes without question that up and down states are due to intrinsic cellular or network mechanisms.  Given the complexity of the ecosystem, it is very probable that high diversity and high density of life is unstable or at least bistable with low diversity and low density.

Clearly ecosystems are not entirely stable since invasive species can cause so much damage.  I can envision a scenario where starting from a barren environment the tendency is to evolve towards more life.  However, as the ecosystem matures and becomes more interconnected it also becomes more unstable because there are more ways for it to fail.  When life is sparse, randomness is your friend because it can lead to innovation and fill niches.  However, when life is dense and mature, randomness becomes your enemy because there are more ways to destroy what you have than to make it richer.  It is like constructing a tower made of toy building blocks.  Initially, it is easy to add to the tower.  However, as the tower gets larger and more complex there are more bad moves than good moves.  Eventually, it reaches a point where all moves are bad and it tumbles down.  This may be what happens to ecosystems.  They simply get too big and interconnected and thus become more sensitive to perturbations.  This may also be what happens to companies and civilizations.  If this is true then there is nothing we can do to prevent the current mass extinction.  It is part of the natural course of life.  The only question is whether we will be among the survivors.

4 thoughts on “Are mass extinctions inevitable?

  1. How about the possibility that evolution has selected neural organizations and plasticity mechanisms that would allow animals that lead the whole ecosystem into a dead-end to react to it and change their behavior radically to avoid this? (this would just be an emergent survival behavior). So that, even without free will, everything would not be as dark as you suggest….


  2. My point is that (and it is highly speculative) the previous mass extinctions may have somehow selected this ability…or something that may give rise to it…
    I mean, the nervous system is plastic. The rules that determine the plasticity were selected by evolution. We might therefore think that our ability to understand, infer and predict events has been selected. Only those animals who can do this managed to survive all the previous mass extinctions.
    Then, as humans are now the majority on Earth, this ability to understand, infer and predict would prevent a forthcoming mass extinction.

    PS: this is very speculative and still unclear to me….


  3. Perhaps humans will survive although I don’t know if it is because we have been selected to do so. The majority of survivors of the last extinction were invertebrates. We evolved from the small mammal precursors that survived.

    In any case it is unlikely we will be able to prevent most of the mass extinction currently occurring. This may not necessarily be a bad thing. I’ve posted before that I think life will continue, it will just be different.


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