More Diversity Or Less?

Nature reviews Biology’s First Law: The Tendency for Diversity and Complexity to Increase in Evolutionary Systems:

McShea and Brandon state that diversity and complexity tend to increase over time in biological systems. It is, the authors argue, a universal law, applicable to all taxa, at all hierarchical levels and at all times. They use the analogy of Newton’s law of inertia — just as it tells us that a body will move with a constant velocity if no forces act on it, this zero-force evolutionary law seeks to capture how a biological system will behave in the absence of other influences. Although the trend they describe may not manifest itself in cases when it is counteracted by constraints, it provides the background against which other evolutionary pressures should be understood.

The authors adopt a simplified measure of complexity that considers only the degree of differentiation among the parts of a biological system, not the various functions of those parts. … The authors argue persuasively that their simpler definition of complexity is more scientifically useful … because function is hard to quantify. … Diversity at one level of the hierarchy equates to complexity one level higher. Both diversity and complexity will increase over time through the accumulation of mutations, they suggest. …

The tendency for increasing diversity has been recognized previously in specific situations. … The authors aim to encompass these various findings in a single theory that covers all of the fields in which the principle has been seen. … They make a good case for their argument that a single principle is at work. …

Their theory suggests new research questions, such as whether the tendency for diversity to increase will usually be overcome by natural selection, and it advances our philosophical understanding of evolution. The law also makes testable predictions: for example, that diversity and complexity will increase fastest in ecological circumstances and taxa where selection is weak.

This is a deliciously vast topic, with huge long term implications. Overall, diversity has clearly increased within biology on average over time. Very recently, humans have displaced other biology diversity with human diversity. Within the human realm, many kinds of diversity have also increased, though some kinds have decreased as well. The big open question: will diversity continue to increase, or at least not greatly decrease, into the distant future?

One the one hand you might think that physics is the same everywhere, matter doesn’t vary that much, and there is only one very best way to arrange atoms for any particular purpose. So within a million years we’ll figure out the most competitive local designs and from then on everyone will use them.  Surely there is a lot of truth in this.

On the other hand, the very best design for any one thing may depend greatly on other choices made nearby, and ancient legacies, choices made long ago that are too expensive to change, may vary greatly from place to place. And there should be far far more places out there, only weakly connected to each other due to vast distances and light-speed limits.

On a third hand (oh someone will have them), the future might not be competitive, if a stable world government arises before our descendants radiate rapidly out into the cosmos, and if there are no aliens that matter out there. Such a stable central power might work to reduce diversity, to cement its hold on power. (More on world govt here, here, and here.) Or perhaps it will have stable preferences, unchallengeable power, and prefer to create diversity.

So, will diversity increase in the long run?

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  • lxm

    will diversity continue to increase, or at least not greatly decrease, into the distant future?

    If you really want to answer this question, then you must discuss the concept of the ‘anthropocene’, a potential name for the current geologic era that says human activities have had a significant global impact on the Earth’s ecosystems.

    One of the impacts is a loss of biodiversity. We are losing 140,000 species/year. Our period will be the sixth greatest extinction event in the history of the planet.

    So when you suggest that the loss of biodiversity is offset by the increase in human diversity, I think you are wrong. When you point to the potential problems of a future world government, I think you miss the point. Humans are the agents, today, that are reducing biodiversity and reducing the ability of the earth’s systems to create more diversity.

    Now I’m no expert in any of this, but I do think this is something to consider.

  • MichaelG

    In the simulated evolution programs I’ve played with, it’s much easier for an organism to just turn off a bit of code, rather than optimize it completely out of the genome. I expect something similar happens in real DNA. Isn’t a large percentage of our DNA non-coding and thought to be this kind of trash?

    So old traits are preserved and new ones are evolved from breeding and mutation. That creates a bias for diversity and complexity.

    If you are talking about the diversity of future civilizations, human or artificial, it would seem this same principle applies. It’s going to be very, very cheap to keep information. Why even throw it away? So information will accumulate, and this can potentially be expressed as new behavior.

  • http://timtyler.org/ Tim Tyler

    Re: “Physics is the same everywhere, matter doesn’t vary that much, and there is only one very best way to arrange atoms for any particular purpose. So within a million years we’ll figure out the most competitive local designs and from then on everyone will use them. Surely there is a lot of truth in this.”

    I am very sceptical. The number of configurations of matter increases exponentially as the number of atoms increases. We know that organisms will have to be large to do things like farm stars. So: the number of combinations to be explored is enormous – and it will take trillions of years to properly explore them.

  • Jason

    I will say yes and no.

    One way to look at life is as a dissipative system that emerges in order to consume free energy and produce entropy more rapidly — like convection cells, or maybe this mechanism for the origin of life.

    Entering a new ecological niche opens up the opportunity to consume untapped free energy. Sometimes there are collapses in this process — if you turn down the heat, at some point the convection cells in your boiling water will go away, or maybe a disease will consume free energy more rapidly than is sustainable and you get an epidemic that stunts the overall production of entropy by killing off the hosts.

    But “life will find a way” to get at that new free energy surplus. Diversity will increase (information will increase), and free energy will be consumed at an increasingly rapid rate.

    However, at some point, too much of the free energy will be consumed to sustain particular dissipative systems, and they will stop. Life only adds a few percent to the total entropy production of the earth, most of it is produced by the atmosphere, so either we or some surrogate find a way to get off the planet, or we fade away, going “backwards” in evolution until only bacteria, then temperature gradients, then nothing except the heating of the rocks and the re-radiation can survive.

    Of course, the whole universe operates in the same way … the biggest producer of entropy is starlight shining on dust. Eventually almost all the free energy will be consumed and that will be the only dissipative system still operating.

    (The articles I’ve linked to are not exactly in the textbooks yet, so this picture may be entirely wrong.)

  • Matt

    lxm:One of the impacts is a loss of biodiversity. We are losing 140,000 species/year. Our period will be the sixth greatest extinction event in the history of the planet.

    Previous extinction events seem pretty small in the context of the overall trend – http://en.wikipedia.org/wiki/Phanerozoic.

    Also note extinctions tend to increase in intensity over time – http://en.wikipedia.org/wiki/File:Extinction_Intensity.svg. A greater % of genera become extinct in each extinction, even as the absolute number of genera increase!

    Perhaps these also are interlinked?

    • Matt

      Sorry, extinctions rather decreasing than increasing…

  • http://akinokure.blogspot.com agnostic

    This is an empty way of phrasing their argument — that in the absence of forces like natural selection, diversity tends to increase because of mutation. Well, obviously. You could say it the other way around — if it weren’t for those darned mutations and migration bringing in new variants, the “basic tendency” is for diversity to be removed by positive selection as well as by random drift.

    Also, diversity can be maintained by natural selection through a variety of ways, the most famous being frequency-dependent selection, like the Hawk-Dove game shows. It’s only when one form is universally better that it displaces the other, removing diversity.

    Arguing which forces we should view as more “basic” has gone nowhere because all are always operating. Focusing on mere diversity and complexity also seems like a step backward conceptually — we care about what shows sophisticated design, too, and that only comes from natural selection, not from a series of unselected mutations.

  • Aron

    Uniformity is unstable.

    We could have had GreenGrassRabbitFoxes as the sole species on the planet that hunted each other and also performed photosynthesis. Sometimes they used their pointy teeth to rend and gnash flesh, and sometimes they just grazed on the outcropping of photosynthesizing fur. It didn’t happen.

    I pity a world created by human imagination. How droll it would be. The universe contains vastly more computational power, and it’s selective process is far more creative.

  • http://timtyler.org/ Tim Tyler

    Re: “will diversity continue to increase, or at least not greatly decrease, into the distant future?”

    The total amount of genetic information is likely to increase – since the number of unexplored niches is large, and living systems will develop systems that exploit them.

    Will there be lots of creatures – or one big one with many manifestations? It is hard to say for sure – except at small scales, where there will *probably* still be something *like* bacteria – which will still necessarily be capable of independent reproduction and so probably evolution.

    So – based on the idea of the existence of many small independent creatures, and the existence of very many unexplored niches for them, it seems as though diversity is likely to continue to increase in the long term – though maybe it depends somewhat on exactly how “diversity” is defined and measure.