Bats and predictability

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ScienceDaily reported a few days ago on an interesting story (actually, a journal article in the April PLOS Biology) about how bats track insects they want to catch in a way that is very different from that of humans and some other animals. Essentially, humans, fish, dogs, and others use a strategy the article calls "constant bearing" to follow things -- basically, they just head straight for their target. Bats, on the other hand, actually take into account the target's velocity and direction and flies partially parallel to the target. In other words, bats work out in advance where they think their targets will be, and head there, rather than directly towards the target, which saves time.

This is pretty interesting. Even further, the article points out that this is a strategy similar to that developed by engineers for guided missiles.

But here's the part I find the most interesting:

This study also demonstrates, for the first time, that bats work out ahead of time how they will catch an insect. Evolutionary pressure to catch flying insects as fast as possible, the researchers speculate, may have pushed the bat to adopt this technique to catch a meal on the go as quickly as possible. Their paper appears in the May issue of PLoS Biology.

There is no mention of evolution in the journal article, so I assume ScienceDaily must have talked to the researchers. But the article also points this out:

The pursuit strategy is different from that reported in earlier studies of target pursuit in humans and other animals.

Now, my gripe is this:

Evolution is invoked as an explanation of why bats fly this way -- they need to catch their prey as quickly as possible. Does that mean that humans and other animals don't need to catch their prey as quickly as possible? It really seems like a useless remark to me. As far as I can tell, it is completely impossible to predict based on the theory of evolution whether a particular kind of animal will follow use one search strategy or another. It's purely a subjective opinion of the researcher -- these researchers think it fits with evolution (indeed, it must fit with evolution if bats evolved!), but I suppose another researcher could disagree. In other words, evolution really has no explanatory power in this case. Essentially, it just amounts to saying, "Well, bats which track their prey that way survive better, so of course they fly that way!"

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Essentially what Abednego has stumbled upon is that evolution is useless for predicting things. This is why there are many researchers who don't think the theory of evolution is important for their research. Just as in this article it was not whether t... Read More

5 Comments

Isn't it sort of shorthand for saying that mere chance produced a mutation that ended up being conducive to survival and reproduction, and thus the trait survived rather than the simple structures that didn't have this nice effect? It's an explanation of how the trait would survive if it could occur, without actually saying anything about what brought it about in the first place. I think that does count as a sort of explanation, but I think you're right that they're misstating what the explanation is, and they're misstating how much it's actually explaining.

I agree that it is an explanation in some sense -- but what I'm trying to point out is that one could apply the same argument to humans and other animals, and come to the same conclusion. That is, if we say, "Evolutionary pressure means that animals and humans should catch their prey as quickly as possible," we would predict that both bats, dogs, and humans will use the targeting strategy used by bats. Yet dogs and humans don't, but this doesn't particularly seem to bother anyone. Apparently, evolution is flexible enough that it can explain why bats use this strategy, but it also doesn't have any problem with the fact that dogs and humans don't.

I guess what I'm saying is that it's apparently only useful as a post factum explanation, rather than a prediction, which is less than ideal, from a scientific perspective. For example, I spend a lot of time in my research making predictions for experimentalists to test (I do theoretical research). People would think my research was pretty lame if I could only explain observations and never predict them -- they would argue that I don't really understand the theory, otherwise I would be able to predict the observations rather than just explaining them.

I suspect that the point was that bats need to catch flying insects as quickly as possible -- i.e., an unusually erratic target. Constant bearing, on the other hand, is only the time-optimal solution for achieving a target that is not moving erratically. As far as prediction and checking the speculation goes, I suppose one would have to look at other animals that catch flying insects in flight.

Brandon...an erratically flying insect would mean that prediction based on velocity and direction would be less useful.

The article's evolutionary explanation sounds rather Lamarckian to me. It's like saying giraffes grew long necks in order to eat leaves from tall trees.

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