Sunday, June 16, 2013

Evolutionary traps

In this post, Carl Zimmer writes:
We have altered the environment in a vast number of ways, both small and large. And when animals try to read the cues from our human environment, they can get tricked. They can end up doing something that kills them, loses them the opportunity to reproduce, or simply wastes their time. Scientists call these situations evolutionary traps.
This reminded me of an evolutionary trap that Richard Dawkins described in The Extended Phenotype:
Moths fly into candle flames, and this does nothing to help their inclusive fitness. In the world before candles were invented, small sources of bright light in darkness would either have been celestial bodies at optical infinity, or they might have been escape holes from caves or other enclosed spaces. The latter case immediately suggests a survival value for approaching light sources. The former case also suggests one, but in an indirect sense...Many insects use celestial bodies as compasses.Since these are at optical infinity, rays from them are parallel, and an insect that maintains a fixed orientation of, say,30 degrees to them will go in a straight line. But if the rays do not come from infinity they will not be parallel, and an insect that behaves in this way will spiral into the light source (if steering an acute angled course) or spiral away (if steering an obtuse-angled course) or orbit the source (if steering a course of exactly 90 degrees to the rays). Self-immolation by insects in candle flames, then, has no survival value in itself: is a byproduct of the useful habit of steering by means of sources of light which are 'assumed' to be at infinity. That assumption was once safe. It now is safe no longer, and it may be that selection is even now working to modify the insects' behaviour. (Not necessarily, however. The overhead costs of making the necessary improvements may outweigh the benefits they might bring: moths that pay the costs of discriminating candles from stars may be less successful, on average, than moths that do not attempt the costly discrimination and accept the low risk of self-immolation...)
As for using language like moths 'assuming' something or overhead costs outweighing benefits, which may sound as if moths are doing such calculations, see Dawkins' reply to Mary Midgely's criticisms of The Selfish Gene (pdf). 

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