13 May 2009

Natural Selection and Strictly Contextual Heirarchy

Ken MacLeod has a post up on Jerry Coyne's "Why Evolution is True"; if one follows along to the blog post about Richard Lewontin's review, one can find a discussion of the criticism that while evolution—change in the type and kinds of living things over geological time—is incontrovertible, the status of natural selection as the explanation is less strong, and the sufficiency of natural selection ought not to be presumed. ("that the evidence for natural selection as the driving force of evolution is of the same inferential strength as the evidence that evolution has occurred", to quote the review.)

Coyne's discussion of the evolutionary issues is much, much better than mine could possibly be, so I'm going to leave it under that third link up there and talk about a meta-issue.

Natural selection is one of those mercilessly simple ideas, like charge or gravity, that can give useful results right away and still have people wrestling wih the fine points a century or more later. It says that there will be statistically significant differences in reproductive success based on the interactions between the variation between organisms in a population and the environment of those organisms, and that this can eventually lead to populations of organisms distinct from the original population.

Which is one of the major problems with getting people to think about natural selection; it's all probabilistic. People are bad at thinking about probability.

But, anyway, that is a well understood problem. One of the problems which does not appear to me to be well understood—I read a lot of this stuff, some of it from the technical literature—is that the notion of "fitness" is not merely contextual, it is dynamic.

Consider a day with a surprise hail storm, one that involves substantial hail that could cause real injury.

If you're at the park, and you happen to have an umbrella, the cost of carrying the umbrella is offset by the benefit of not being struck on the head by the hail and injured. It's even better if you're under a strong roof, and better still if you happen to be somewhere the hail isn't falling, but let's just consider the umbrella/no umbrella case.

Carrying the umbrella is work; it uses up a hand, or space in a bag; you have to remember you've got it and not lose it, you have to manage it in crowds, and it might not rain, never mind hail. People who see you may treat it as a social signal; the content of the signal will vary, both depending on whether or not it is raining and depending on social expectations; some of the social expectations will result in a negative evaluation. (Which is to say, most people seeing you bring an umbrella to the park on a sunny day will decide you're timorous, stuck-up, or silly, rather than careful, prudent, or practical.)

Not having an umbrella if it rains means you get wet; this might not matter (you're going straight home, where you can get warm, dry, and fresh clothes) or it might matter a lot (it's cold rain, it's going to go on for a long time, and you have no where to go; hypothermia and death are real risks). If it's hailing, you might, instead of getting wet, wind up injured or killed. Certainly, looking like someone has thrown five or six buckets of ice cubes in your face won't enhance your reproductive success.

The trade-offs are (I hope) obvious; what is not obvious, what is painfully slippery, is that the evaluation of the trade-offs changes continuously; the weather is always changing. The other people seeing you with your umbrella have different views depending on the weather: you look prudent in the rain, paranoid in the warm sunshine, prescient in the hail. Their own history and expectations alter what the other people see; someone who had a horrible experience being caught in cold rain on their way to an important social function is going to see someone with an umbrella on a sunny day differently than someone who more or less doesn't doesn't care about being rained on.

The real trade-offs are much more complicated than the umbrella case. (What makes you less of a target for one predator might make you more of a target for another, for example.)

In the human case, the failure mode comes from thinking fitness as static; that you can take the media or mean utility of carrying that umbrella and derive a stable hiearchy of fitness from it.

Or, more accurately, you can derive that stable hierarchy—something people certainly do—but err in treating it as meaningful.

Humans gang up on problems; that's the basic human thing. What problem means "what hierarchy?" because different people have different skills, just like "what does today's weather forecast say?" has different implications for how likely you are to carry an umbrella.

It is my suspicion that the people objecting to natural selection as the mechanism for evolution have not made the necessary mental leap to recognize that the hierarchy of selection under natural selection is dynamic and unstable. Natural selection, rather than implying a fixed order of superiority, implies an impossibility of fixed order and a necessary recognition of context in human social organization. (Not to mention recognizing that the purpose of social efforts to produce a fixed hierarchy is necessarily not efficiency or optimal results for anyone other than those located at the pinnacle of that fixed hierarchy.)

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