The Country Bird and the City Bird, Redux

In this post, I asked what economic principle would illuminate the change in bird behavior shown between country birds and city birds. In class, I used this to illustrate marginalism: in any population, their will be individuals living at different margins of the species range, whether that is a geographical range or a range of behaviors. In this case, there must always have been some birds who lived close to the margin where a human would snatch them if they were any more daring: after all, there is food to be had at that margin! If their offspring were just a little more daring... lunch!

But as humans settled in cities and hunting became less important too them, the safe distance would move a little closer. Now those supra-marginal birds survive, and get the pickings available just a bit closer to humans. And so on.

Evolution is driven at the margin.


  1. That's a pretty neat illustration. But it treats the birds purely as objects, rather than also as subjects (i.e., it makes their behavior a purely a function of genetics and dismisses the possibility of free-will).

    I suspect there is a subjective element to it as well -- the birds can, to a degree, choose to adjust their own behavior, depending on the circumstance. Maybe a worm couldn't choose, but I'll bet a bird can.

    (To take it further, there might also be epigenetic phenomena -- maybe the experience of living in city vs. country alters gene expression. If you grew up way up in the Andes, you'd probably be a stocky little guy with enormous lungs and a lot of iron in your blood -- independent of natural selection or your own freely chosen attempts to acquire such traits. Maybe the lower stress environment of the city causes changes in gene expression that let the birds relax and experiment with risky behaviors they otherwise wouldn't try.)

    I'm probably taking this analogy way too far...

    1. "But it treats the birds purely as objects, rather than also as subjects (i.e., it makes their behavior a purely a function of genetics and dismisses the possibility of free-will)."

      Absolutely not, Scott. I specifically told my class I was making no behavioral assumptions about the birds. The behavior could be completely freely chosen: nonetheless it is the birds at the edge of the range of choices who will push that range out further as human behavior changes. Marginalism seems to apply to life, whatever cognitive assumptions we make about various forms of it.

    2. Hmmm... I was thinking that if the birds could change themselves, then there would be no definable 'distribution' to talk about. But I suppose I was making the error of the Greek philosophers about the natural sciences -- actually, we can change our own minds, too, but that doesn't obliterate the science of economics. At any given moment, there does exist some concrete distribution for which there is a margin, even though supply and demand schedules are changing all the time.

      You're right, it does seem to apply more broadly than just to evolution.

  2. Anonymous10:48 PM

    Just out of curiosity, what exactly does bird activity have to do with economics? I'm serious.

    I understand your thinking here, and it is interesting (as is the correlation), but it isn't economics. Maybe an "economics ... of such and something or other", but not economics in terms of human thought (which is the realm of economics).

    If you want to get even more involved, take a look at specific birds, such as pigeons. Or, for 4-legged land creatures, raccoons are a good study. But I wouldn't call that economics.

    1. Well, I didn't call it economics, but *much* of economics can be applied to non-human critters in a very straightforward fashion. The history of back and forth between economics and biology is extensive.

    2. BTW, I used to flip through a journal called Proceedings of the National Academy of the Sciences (or something like that -- we always referred to it as PNAS) looking for other stuff, and every now and then I would see an article on these kinds of things.

      I do not know how big this journal is in economics circles, but you might want to check it out. (Or maybe you already know a bunch of better sources for this stuff...)

    3. Indeed. Game theory. Game theory works better in biology IMO despite starting in Econ. And evolutionary stability in GT started in biology.

      I like the marginal ism point btw.


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