Growth Could Slow

Human history has seen accelerating growth, via a sequence of faster growth modes. First humans grew faster than other primates, then farmers grew faster than foragers, and recently industry has grown faster than farming. Most likely, another even faster growth mode lies ahead. But it is worth remembering that this need not happen. For a very concrete historical analogue, the Cambrian Explosion of multi-cellular life seems to have resulted from an accelerating series of key transitions. But then around 520 million years ago, after life had explored most multi-cellular variations, change slowed way down:

In just a few tens of millions of years – a geological instant – almost every major animal group we know made its first appearance in the fossil record, and the ecology of the planet was transformed forever. …

Scientists have struggled to explain what sparked this sudden burst of innovation. Until recently, most efforts tried to find a single trigger, but over the past year or two, a different explanation has begun to emerge. The Cambrian explosion appears to have been life’s equivalent of the perfect storm. Instead of one trigger, there was a whole array of them amplifying one another to generate a hotbed of animal evolution the likes of which the world has never seen before or since. …

The first sign of multicellular animals is in rocks about 750 million years old, which contain fossilised biomolecules found today only in sponges. Then another 150 million apparently uneventful years passed before the appearance of the Ediacaran fauna. This enigmatic group of multicellular organisms of uncertain affinities to other lifeforms flourished in the oceans up to the beginning of the Cambrian. Then [110 million years later] all hell broke loose. … Studies of “molecular clocks” – which use the gradual accumulation of genetic changes to estimate when particular evolutionary branches diverged – suggest that animal complexity emerged before the Cambrian. …

Two huge ecological innovations that make their debut in the Cambrian fossil record. …The first is the ability to burrow into the sea floor. … The second innovation was predation. … What else were these early creatures waiting for? One intriguing possibility is that they were waiting for fertiliser. Geological evidence suggests that rising sea levels during the Cambrian could have increased erosion, boosting levels of nutrients such as calcium, phosphate and potassium in the oceans. …

Atmospheric oxygen levels crept up gradually. … The crucial threshold seemed to be between 1 and 5 per cent of present oxygen levels. Geochemists’ best guess at when the ancient oceans reached this point is about 550 million years ago – just in time to kick off predation and its resulting ecological feedback. …

Precambrian oceans were full of single-celled algae and bacteria. When these small cells died, they would have started to sink, decomposing quickly as they went – and because decomposition consumes oxygen, this would have kept ocean waters anoxic. Filter-feeding sponges, which evolved sometime before the Ediacaran,then started clearing these cells out of the water column before they died and decomposed. The sponges themselves, being larger, were more likely to be buried in the sediment after death, allowing oxygen to remain in the water. Over time, this would have led ever more of the ocean to become oxygenated. (more)

So it remains possible that growth will slow down now, or after the next transition, even if a new series of accelerating transitions lies far ahead.

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  • Foo McBarson

    This seems like a case where the outside view is very weak compared to the inside view. It’d be like trying to figure out the prognosis of a patient with pneumonia and, instead of looking at a meta-analysis or randomized controlled trial, we looked at a case study of a patient with lung cancer, a case study of a patient with asthma, and a case study of a patient with the common cold. (Not saying the inside view is much better.)

  • joeteicher

    >Most likely, another even faster growth mode lies ahead.

    You like to speculate about a faster growth mode lying ahead but “most likely” seems like a stretch. Is there any reasonable way to put a probability on it?

    • http://overcomingbias.com RobinHanson

      The data is that the three most recent mode switches along this path were to much faster modes. No switches to much slower modes. That seems sufficient to suggest “more likely than not”, in the absence of contrary indications.

      • http://juridicalcoherence.blogspot.com/ Stephen Diamond

        One can probably find many contrary indications: for example, regression toward the mean comes to mind as a logical argument as to why the rate of change will slow.

        [As empirical evidence, the unidirectionality of three mode shifts doesn’t even reach the .1 significance level.]

      • joeteicher

        I can think of a few contrary indications.

        1. We know that even current growth rates are not sustainable in the long run (maybe a few thousand years). So, we know growth is going to basically 0. Why not draw a line from where we are at now to there? That’s a lot simpler than predicting a large jump in growth rate followed quickly by a massive deceleration to below where we are now.

        2. The Fermi paradox. One plausible candidate for the great filter is just that the universe doesn’t cooperate with sci-fi scenarios and we are closer to the end of innovation than the beginning.

        3. The fact that growth rates have noticeably slowed for developed economies also argues for deceleration rather than acceleration.

      • Dave Lindbergh

        Re 2 – If the “perfect storm” idea is right re the Cambrian explosion, that seems a pretty good explanation of the Fermi paradox.

        Re 3 – That’s just a catch up effect. It’s easier to catch up than to break new ground. Doesn’t have much effect on the global long-term growth rate.

      • http://overcomingbias.com RobinHanson

        The fact that in the very long run growth must slow gives only a very weak prediction about how the next mode compares to the current mode. The more total modes there were and will be, the weaker this indication is.

      • http://juridicalcoherence.blogspot.com/ Stephen Diamond

        And how strong a prediction is provided by a short string of prior (as far as we know, unrelated) transformations?

        How, pray tell, do you compare the predictive power of these opposed (very weak) clues?

      • IMASBA

        I’m not sure you can apply statistics to this, not until somebody offers a clear definition of a “mode switch” (right now we could interpret the term so that there were more than three mode switches).

      • http://juridicalcoherence.blogspot.com/ Stephen Diamond

        If not statistics, what kind of reasoning?

      • Mark Bahner

        1. We know that even current growth rates are not sustainable in the long run (maybe a few thousand years). So, we know growth is going to basically 0.

        I don’t know that. I think the growth in per-capita gross world product will continue to accelerate, barring global thermonuclear war or takeover by Terminators. This will continue until money is basically meaningless. (If everyone in the world has the wealth of Bill Gates, I don’t see any meaning to money.)

        “2. The Fermi paradox. One plausible candidate for the great filter is just that the universe doesn’t cooperate with sci-fi scenarios and we are closer to the end of innovation than the beginning.”

        The “universe” stopping global economic growth seems like a mystical proposition to me.

        “3. The fact that growth rates have noticeably slowed for developed economies also argues for deceleration rather than acceleration.”
        The trillion dollar questions are why this has happened, and whether its likely to continue. My personal guesses are that: 1) population growth has slowed in these countries (they’ve aged), and 2) this is not likely to continue, because computer brains will replace (and vastly exceed) human brains.

  • IMASBA

    “So it remains possible that growth will slow down now, or after the next transition”

    Uhm, yeah, but we already knew that. Natural resources are limited and at some point we will have exhausted all the low hanging and even most of the high technological-breakthrough fruit…

  • http://www.stafforini.com/ Pablo Stafforini

    Robin, how evidentially significant should we regard a trend of the sort you describe in the absence of an obvious underlying mechanism? What is the track-record of extrapolations from such trends? Are there other considerations that we can rely upon to estimate more precisely the degree to which that trend supports your predictions?

    • IMASBA

      The underlying mechanism is formed by breakthrough technologies: fire, complicated language, domestication of anmials, boats, agriculture, pottery, metal working, writing, mathematics, aquaducts/irrigation, the steam engine, hygiene, electricity, radio, the transistor, etc… and we know there are more to come (advanced bioengineering, clean energy sources, artificial intelligence).

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  • Stuart

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