Random Interesting, Thoughts

Dinosaurs and Tail Risk

Writing in this morning’s FT, Nassim Nicholas Taleb proposes Ten principles for a Black Swan-proof world:

1. What is fragile should break early while it is still small. Nothing should ever become too big to fail. Evolution in economic life helps those with the maximum amount of hidden risks — and hence the most fragile — become the biggest.
…
Then we will see an economic life closer to our biological environment: smaller companies, richer ecology, no leverage.

A sensible plan, but unfortunately Mr. Taleb’s faith in biology is misplaced.

Why the Dinosaurs got so Large

19th-century palaeontologist Edward Drinker Cope noticed that animal lineages tend to get bigger over evolutionary time, starting out small and leaving ever bigger descendants. This process came to be known as Cope’s rule.

Getting bigger has evolutionary advantages, explains David Hone, an
expert on Cope’s rule at the Institute of Vertebrate Paleontology and
Paleoanthropology in Beijing, China. “You are harder to predate and it
is easier for you to fight off competitors for food or for mates.” But
eventually it catches up with you. “We also know that big animals are
generally more vulnerable to extinction,” he says. Larger animals eat
more and breed more slowly than smaller ones, so their problems are
greater when times are tough and food is scarce. “Many of the very
large mammals, such as Paraceratherium, had a short tenure in the
fossil record, while smaller species often tend to be more
persistent,” says mammal palaeobiologist Christine Janis of Brown
University in Providence, Rhode Island. So on one hand natural
selection encourages animals to grow larger, but on the other it
eventually punishes them for doing so. This equilibrium between
opposing forces has prevented most land animals from exceeding about 10 tonnes.

Dinosaurs had skewed incentives and took on too much tail risk! If even evolution falls into this trap, God help the bank regulators…

  • Two things:

    1) Evolutionary history is chock full of failed strategies. Organisms that couldn’t tolerate oxygen died with the advent of photosynthesis. Countless others were exterminated through competition.

    2) Evolution is an undirected process regulated only by death and reproduction. An intelligently designed and operated system ought to be able to do better in many cases.

    That being said, the analogy is an interesting one. Also, ‘tail risk’ is an amusing concept for dinosaurs.

  • 1) Evolutionary history is chock full of failed strategies.

    2) Evolution is an undirected process regulated only by death and reproduction. An intelligently designed and operated system ought to be able to do better in many cases.

    Right, absolutely. Search is blind, and organisms are littered with local minima – the laryngeal nerve in the giraffe, the inverted retina in mammals, etc, etc. I think, though, we should give evolution a little credit – to some extent it has evolved to avoid its own pitfalls. Take segregation distorter effects:

    Segregation-distorters subvert the mechanisms that usually guarantee fairness of sexual reproduction. For example, there is a segregation-distorter on the male sex chromosome of some mice which causes only male children to be born, all carrying the segregation-distorter. Then these males impregnate females, who give birth to only male children, and so on. You might cry “This is cheating!” but that’s a human perspective; the reproductive fitness of this allele is extremely high, since it produces twice as many copies of itself in the succeeding generation as its nonmutant alternative. Even as females become rarer and rarer, males carrying this gene are no less likely to mate than any other male, and so the segregation-distorter remains twice as fit as its alternative allele. It’s speculated that real-world group selection may have played a role in keeping the frequency of this gene as low as it seems to be. In which case, if mice were to evolve the ability to fly and migrate for the winter, they would probably form a single reproductive population, and would evolve to extinction as the segregation-distorter evolved to fixation.

    I would guess any number of species went extinct through this process until mechanisms evolved to suppress this kind of short-term dead end. The banking equivalent would be a trader who bets the whole bank on a one-way punt on gas prices. Banks that allow that kind of trader to operate go extinct very rapidly.

    So it’s interesting that evolution doesn’t seem to have come up with a way to deal with the tendency towards exposure to risk for very infrequent events. Not surprising really – there haven’t been many instances to learn from, and any mechanism to prevent these risks would have to be mind-bogglingly robust – surviving intact through tens of millions of years of genetic drift, without any reinforcement along the way to keep it intact (indeed, negative reinforcement, due to the short-term payout).
    This strikes me as exactly the same problem we face with the banks – by the time the next crash comes around, whatever mechanisms we put in place now will have been eroded away.
    Maybe our far-seeing regulators can set up protective restrictions that will endure for 100 years, but God help them, the odds are against them.

  • “So it’s interesting that evolution doesn’t seem to have come up with a way to deal with the tendency towards exposure to risk for very infrequent events.”

    I think it has, in the form of extreme diversity: everything from sulphur-eating bacteria to pandas. Of course, that isn’t much help to particualar species faced with a major and immediate threat.

  • I thought you might like to know that I picked up a copy of a book you recommended:

    MacKay, David. Sustainable Energy – Without the Hot Air.

    I will post a review when I finish it.

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