Sunday, February 26, 2012

The Ugliness of the Leaf-Nosed Bat

 
Here's a photo of the head of a leaf-nosed bat. I was posted on Jerry Coyne's blog website today [A new leaf-nosed bat]. Jerry is discussing an article in National Geographic: Strange New Leaf-Nosed Bat Found in Vietnam. You'll probably be curious about the strange appearance of this bat's face. How did that happen?

Well, there are several possibilities that account for the evolution of ugly bats. I wonder what Coyne says ....?
Leaf-nosed bats are found in both the New and Old World, and the New World ones are the most numerous group in the order Chiroptera (bats), which itself is one of the most diverse order of mammals, second only to rodents (40% of mammal species are rodents; 20% are bats). A probably aprocryphal story relates evolutionist J. B. S. Haldane’s answer when asked what one could infer about the Creator from surveying his creation. ”An inordinate fondness for beetles,” Haldane supposedly said. (Of the roughly 1.7 million described species on Earth, 300,000-400,000 are in the order Coleoptera—beetles.) If that question were asked about mammals, one could reply that God showed an inordinate fondness for rodents and bats, and a notable distaste for primates.

The function of the “leaf” isn’t fully known, but it’s suspected to be important in receiving the echolocation signals emitted by bats.

You may find this beast ugly, but that’s speciesism! I find all animals beautiful because they’re products of evolution, embodying all the mechanisms that drive the process. The ugliness, in this case, is probably a byproduct of natural selection.
Why should we assume that the ugliness is a byproduct of natural selection? Lot's of humans are ugly, is that also a byproduct of natural selection? :-)

Seriously, we don't know why these bats have such faces. Why couldn't it just be an accident of evolution? I'm not saying that this is necessarily true. What I AM saying is that it's wrong to just ASSUME, without evidence, that such an appearance is probably due to natural selection. I bet I would get lots of flak if I said that it was probably due to random genetic drift.


9 comments :

  1. ... it’s suspected to be important in receiving the echolocation signals emitted by bats.

    The ears of the bat are used for receiving the signals. The mouth transmits the signal. It may be important in transmitting the echolocation signals.

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    1. You beat me to it! But, I thought that some bats, like the leaf nosed bats, use their nose to transmit the echolocation calls.

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  2. Can something interesting be said about the relation between 'naturally selected for' and 'accident of evolution' generally? Can f.e. large comparative studies across species be done such that one can say with confidence "this was not selected for" about some trait/ability/etc.?

    (I know very little about biology, so sorry if this is a offensively stupid question).

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  3. Scientists have studied leaf-nosed bats before, and they've found that the structure of the leaf affects the sounds they produce for echolocation. They've concluded that differences in leaf shape probably have to do with their ecological niches.

    Here's an open access paper from 2010: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0011893

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  4. Is ugliness a property of the bat's face or is it a property of our own sense of aesthetics?

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  5. I'm sure Leaf-nosed bats of the opposite sex find that face quite attractive so the designation of ugly is anthropomorphic.

    As to whether it's wrong to assume natural selection versus genetic drift, would that not be a function of how useful and successful an a priori assumption of one or the other has been in the past ?

    And finally, there are other species, such as owls, where the shape of the face helps in focusing the audio signal.

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  6. Seriously, we don't know why these bats have such faces.

    What you mean to say is that you don't know. It's an argument from ignorance. As Carl Zimmer indicates above, some people actually know something about animals and try to test their hypotheses instead of just opining.

    Why couldn't it just be an accident of evolution?

    It could, but mitigating against that hypothesis are the fact that the trait characterizes an entire clade of bats, with several species, in each of which it has been exposed to natural selection over millions of generations. It's still here, in all of them, and therefore very likely has a function.
    Plus the direct tests mentioned.

    I bet I would get lots of flak if I said that it was probably due to random genetic drift.

    No, just the usual rolled eyeballs at you and your hobbyhorse.

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  7. Of course it's a property of our own aesthetics.

    Beauty and ugliness are human concepts.

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  8. AL, Jerry wasn't arguing that ugliness was an adaptation, he was arguing that the complex nose structure was an adaptation.

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