Patrick O'Brian Discussion Forum


Re: I wrote sloppily

Kate Bunting


On Sat Aug 26, Bob Bridges wrote
--------------------------------
>I was thinking that everyone had the same experience in school that I did, so I encapsulated briefly and sloppily, expecting everyone to know what I meant.  Sorry, my bad.  Here's the same thing written out in longhand:

>When I was in high school, say in the late '60s, I was taught that pollution in London had gotten so bad that soot and other particulates had darkened the tree trunks, and that moths with light-colored wings were more visible to their predators.  But after a while, moths with darker wings started showing up, more difficult to see.  It's been a lot of years but as I recall this was explained to me, or at least I understood it at the time, as a minor example of evolution in action: The light-winged moths were dying off, but as a species evolved darker wings to survive.  At the time I accepted it.

>I later heard the pollution had been somewhat cleared up, the tree trunks began to show lighter in color, and the same process of evolution worked in reverse, that is, moths began to have light wings again.

>Later still, when I was in my 20s or 30s I suppose, I read that this is not to be considered an example of a species of moth evolving to survive changing circumstances; there were simply two species or perhaps subspecies of moth.  As the tree trunks darkened, the [sub]species with lighter wings became rarer and the [sub]species with darker wings began to do better.  The reverse happened as the pollution was cleared up.  I accepted this explanation as more likely than evolution by mutation.

>For akatow: I don't recall anyone telling me it had happened a century before.  (If 150 years ago now, then about 100 years ago when I was in high school.  Boy, time flies.)  I always thought of it as reasonably current, say during the '40s and '50s.  Placing it toward the end of the Industrial Revolution makes more sense.

>For YA: As I said, I wrote sloppily.  The above may have made it clear, but when I said the moth species didn't adapt, I meant that a species didn't change their genes to start producing darker wings, but that one species of moth started to do better than the other under the changing circumstances.

>Now that I'm required to think about this whole thing, I realize that I don't really know what was happening.  Were the observers at the time mistaking the light- and dark-winged moths for members of the same species?  Were they the same species?  depression at not being able to affect color change by force of will, I missed it, and it's moot to my point.  

They were sub-species of moths such as the peppered moth, Biston betularia. See https://en.wikipedia.org/wiki/Industrial_melanism

Kate (who hasn't posted on this forum for ages!)


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