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Once there was a final shortlist of 87 DNA differences between the black and pale lab moths, he and his colleagues tested whether each variation, one by one, was present in the wider variety of white moths found in the wild.
"After a long time we eventually managed to get down to a single one, which then had to be the causal mutation. To our surprise, it also turned out to be a rather unusual type of mutation."
The carbonaria mutation was in fact a "jumping" piece of DNA, called a transposon, which had inserted itself into a gene called cortex.
These odd sequences more often have a damaging effect when they disrupt an existing gene. But for one embryonic moth in the early 19th Century, when these extra 9,000 bases landed in its cortex gene, they were in fact the secret to success.
"You can take a sample of chromosomes in the present population, identify all the sequence variance around the mutation, and infer… the number of generations that it would take for that amount of scrambling to occur in the flanking sequence," explained Dr Sacchieri.
Specifically, they estimate the DNA jump happened in a 10-year window centred on 1819 - a date that fits perfectly with a gradual spread of the mutation through the population, until black moths were first spotted in 1848.
The evolution of the peppered moth is an evolutionary instance of directional colour change in the moth population as a consequence of air pollution during the Industrial Revolution. The frequency of dark-coloured moths increased at that time, an example of industrial melanism. Later, when pollution was reduced, the light-coloured form again predominated. Industrial melanism in the peppered moth was an early test of Charles Darwin's natural selection in action, and remains as a classic example in the teaching of evolution. Sewall Wright described it as "the clearest case in which a conspicuous evolutionary process has actually been observed."
Colour variation in the peppered moth Biston betularia was long accepted to be under strong natural selection. Melanics were believed to be fitter than pale morphs because of lower predation at daytime resting sites on dark, sooty bark. Melanics became common during the industrial revolution, but since 1970 there has been a rapid reversal, assumed to have been caused by predators selecting against melanics resting on today's less sooty bark. Recently, these classical explanations of melanism were attacked, and there has been general scepticism about birds as selective agents. Experiments and observations were accordingly carried out by Michael Majerus to address perceived weaknesses of earlier work. Unfortunately, he did not live to publish the results, which are analysed and presented here by the authors. Majerus released 4864 moths in his six-year experiment, the largest ever attempted for any similar study. There was strong differential bird predation against melanic peppered moths. Daily selection against melanics (s ≃ 0.1) was sufficient in magnitude and direction to explain the recent rapid decline of melanism in post-industrial Britain. These data provide the most direct evidence yet to implicate camouflage and bird predation as the overriding explanation for the rise and fall of melanism in moths.
originally posted by: Barcs
a reply to: chr0naut
I will concede the claim about 1 generation per year. It's irrelevant and isn't getting us anywhere in the conversation. I still don't agree that 200 generations is too fast for evolution.
This is pure deception. Do you even know what is being said there? Macroevolution happens on a scale that transcends the boundries of a single species. That precisely means that it is the accumulation of numerous small changes. THAT'S what it is. You keep suggesting that macro evolution is a separate mechanism, when it's the same mechanism over more time. This is now the 3rd time you've completely ignored the mechanism part of it, and it seems you are doing it on purpose because that is the primary factor in my argument and that's the only way you can continue to exploit semantics. Evolution is evolution. Macro is just the description of the accumulation of tons of small changes. It's pretty simple.
From the Berkley page: "Microevolution happens on a small scale (within a single population), while macroevolution happens on a scale that transcends the boundaries of a single species."
Nothing to do with elapsed time, see, your definition was just plain wrong.
Again. One couple not being able to conceive is not speciation. If a couple can't reproduce, their genetic line dies, so they are irrelevant to speciation of the POPULATION. Please stop using this completely flawed and illogical argument. Speciation is about changes spreading to an entire population group, not just one couple or one individual having genetic defects. It's apples to oranges. Yes single genetic changes can cause defects like that because no particular gene is off limits to mutation. That's not speciation.
I was referring to the mechanisms of genetic bio-incomatibilities that, taken together, we would describe as speciating factors. The fact that you conceive of speciation as something separate to the underlying genetic and biologic mechanisms shows a limitation to your understanding and flawed reasoning.
originally posted by: Barcs
Well, it's too late to edit my above posts, but it seems Chronaut also made the fatal error of assuming that the dark peppered moths are a different species from the lighter ones, so he's been misleading me this whole time, talking about 200 generations for speciation and "conflicting with gradualism." They are actually sub species, which means they are more like different "races" of Biston betularia and can breed. It turns out there are actually 5 sub species of peppered moth, not just 2. That's what I deserve for taking somebody's word for something instead of going straight to the data. As you can see there are no missing evolutionary mechanisms here.
I still need to do further research on this, so by all means, correct me if I'm wrong. All this talk about speciation and genetic isolation, when the variety we observe in the peppered moth is simply a result of natural selection due to better blending in with the environment. I apologize for being a bit lackluster in the beginning, I should have just went straight to the sources and research in the first place instead of endless back and forths over irrelevant red herrings and semantics.
Thanks for motivating me to solve the mystery, Chronaut. Sometimes debating you is like pulling teeth, but it annoyed me just enough to go hard in the paint and figure this thing out. It helped me learn some cool new things, so I appreciate it. It would be nice if Raggedy had a response to those studies that prove natural selection beyond the shadow of a doubt, but I'm not counting on it.
originally posted by: chr0naut
Yet there is a difficulty with the specifics of speciational change, especially with observed instances, where the gradualism and the isolation of the mutating population is absent from the picture.
I am not saying that evolution does not happen as theorised. Just that we have instances where it doesn't and therefore either we need to figure out new processes within evolutionary theory, or to acknowledge that it isn't the only way to achieve the biodiversity we observe, and to rigorously define those alternate processes.
By ignoring that populations consist of individuals and that the genetic changes are expressed fully in individuals before they can spread into populations, you are missing the point that changes that are speciating, no matter how gradually they accrue or how isolated the population, are genetic end of line because the carrier of the accumulated change has no mate. It is a monumental hole in the theory and only by ignoring the actuality of the process of genetic change, can it even be vaguely conceived.
Put simply, the accumulated genetic changes are always expressed in an individual before becoming the basis for a population. Speciating changes are, therefore, always expressed in an individual and that individual can find no mate. It is checkmate for speciation via evolutionary process as it is currently codified.
A few of these 'controversial' things are: ongoing chemical abiogenesis, horizontal gene transfer, catastophism, epigenetics, panspermia and mixes of these things also with evolutionary processes, too.