Finished reading Darwin’s Radio by Greg Bear, and did some more research on the net, to find out what part of that science fiction novel is actually science. Not much.
But…
the theory of gradual minute variations in the genome producing new species over time has always been at odds with the evidence of punctuated equilibrium by which most species seem to evolve.
Fruit fly adaptation is eerie. Under laboratory conditions, fruit flys can adapt to cold environments in a single generation!
Hormones can effect gene expression, and the commonly accepted theory is that all fruit flies have the gene for cold-weather survival. A new generation will only express it if it’s needed. the parents experience codes for cold weather adaptation if it’s needed, and it’s expressed in the genome of their offspring (kind of, I don’t really understand so maybe somebody’ll help me out. I’m a finance guy not a geneticist, Dammit!)
In an article in Evolution Magazine in 1998, a new theory was offered.
In circumstances where adaptation is needed by a population of fruit flies, we do not see gradual minute changes, but rather an explosion of minute changes throughout the population, seemingly seeking a favorable adaptation, or combination of adaptions for the environmental changes. Meanwhile a control population in a stable environment exhibits little or no changes.
SOmething in the genome seems to “know” when change is needed, and supplies it. This meshes exceedingly well with punctuated equilibrium.
The vast functions and mechanisms of the genome are little understood. No purpose or utility can be ascribed to up to 70% of the human genome. Are these traits being preserved for no reason? Or, are they waiting? Are they myriad tiny little adaptations waiting to be expressed when called upon by environmental conditions?
Lamarck was an idiot, I bet he just spent his childhood sitting in the corner of his room, eating away at those paint chips, and mumbling to himself.
Anyway, just thought I’d share a true story, that may be of some interest. Way back when, before the Industrial Revolution, there was a species of white moth that thrived in large numbers somewhere in Massachusettes (I can’t spell, forgive me). This moth lived quite a happy life since it was white and its environment consisted of white birch trees. Blending perfectly with these trees is how the moth survived. Well, with the introduction of factories and machines that emitted smoke, the trees turned a shade of grey. Now, the moth, white as it was, did not blend well with the trees, leaving it as easy prey for other creatures. The species dwindled, but, over a span of many years, something magical (ya right) happened. While there were still a few white moths, grey moths showed up. Blending in perfectly with the soot stained trees. Well, this species thrived just as well as the white moths did. But sadly after again, many years, lots of factories were shut down, lessening the amount of smoke emitted into the air. After a time, the trees returned to their normal white color. This time leaving the grey moths un-protected against predators. Well, suffice to say, the number of white moths increased over time and are thrived as they did once before.
Actually, I read a paper a couple of years ago that presented evidence of directed mutations in bacteria, a la Lamarck, though no one would ever use his name anymore. I know I still have the paper somewhere, but it’s not in my stash at work. I’ll look in my stash at home later tonight. The theory proposed is nowhere near as strong as Lamarck’s ideas and poses no real threat to evolution as we know and love it. If anything, it’s just another mechanism.
um, it was the Peppered Moth in England. The melanism is caused by a single point mutation and is thus at a minimal level in each generation. When the environment changed radically in a short while (the blackening of the trees by Industrial Revolution soot) the melanistic form enjoyed a selective advantage against predation by birds. Relative numbers of the black moths went from (IIRC) less than .2% of the population to over 35%.
A fine example of how environmental pressure can change the allele frequency of a population.
sk8rixtx, you’re thinking of the English moth, Biston betularia. A good background intro to evolutionary bio can be found here, as part of the http://www.talkorigins.org website.
And I’d guess Scylla knows the story pretty well, right Scyl?
I’ll need to pursue it a bit, but I find this to be very appealing. Do you know if any followup to the Evolution Magazine article has been published yet?
Yes, I know about the moths. I’m hoping somebody can set me straight as far as mutation frequency goes. It seems to increase when needed, as if some mechanism says “Oh shit, we got problems, better mutate!”
Vaguely Lamarckian, no?
I still don’t understand the mechanism of the fruit fly single generation cold adaptation. Maybe somebody could explain it in English.
I had always thought the Industrial-Revolution moth situation was due to “survival of the fittest” (I know, that phrase wasn’t coined by Darwin) and not just genetic mutation. Since the gray moths blended in better with the sooty surfaces, they weren’t devoured as much as their lighter cousins. Thus, the majority of the moths that were breeding were gray, creating generations of gray-colored moths. This trend reversed as factories shut down and pollution decreased.
But my EGBOMUOTWOE (‘Educated Guess Based On My Understanding of the Workings of Evolution’) is that the gene required to adapt to cold is already present within the fruit fly genome. The cold-resistant phenotype is triggered by external events, e.g., the temperature turns colder. When the genome is triggered, the mechanism is most likely through hormonal action, as indicated by the OP. That is, during development, or perhaps even during adulthood (I don’t know much about fly hormones…sorry), the change in temperature triggers the release of one or more hormones which will have the physiological effect of making the fly ‘cold-resistant’. Thus, within the short span of a single generation, you get a seemingly cold-resistant variant.
One possible test for this would be to take the cold-resistant variety, subject it to warmer temperatures, and see if the next generation winds up ‘normal’ again.
To be truly Lamarckian (a misnomer, by the way, since the idea was not first proposed by Lamarck, nor was it the cornerstone of his evolutionary ideas), the current generation would have to become cold-resistant, then pass that trait on to its offspring. This does not appear to be the case (I’m unfamiliar with the studies involved, so I really can’t be certain about this).
Of course, it’s also entirely possible that I have no idea what I’m talking about
Jeep’s Phoenix, its the same thing. You just have to ask yourself, “What makes an individual fit?” In the case of the moth, a trait for darker colored wings existed within the population. The trait difference was caused by a mutation. The environmental change caused the grey moths to be less likely to be eaten than white moths. More survived to reproduce, so they appeared in larger numbers. The change caused them to be fitter (I understand that the term ‘fit’ isn’t used in evolutionary biology, but it is useful here to make the comparison between the popular phrase ‘survial of the fittest’ and genetic mutations). This is likely the case with the fruit flies.
In the generation of flies raised in normal conditions, a few individual fruit flies possess the cold weather gene. When the fruit flies are put into the cold the flies that lack the gene die while the cold gene flies reproduce like crazy. The result: the next generation is resistant to the cold because they are the offspring of the flies that possessed the gene. Its not really possible to say when the mutated gene entered the population. It may have happened years before your fruit fly experiment. But somehow some the specialized genes made it into your fly sample. The exposure to cold did not cause the mutation to occur nor was it always there in every fruit fly waiting to emerge.
What Mauve Dog said sounds reasonable, but this would not be evolution. The flies that change in this way are already adapted to the cold before they are put into the environment. They genes are the same just which genes are expressed are different (from the first generation to the second). Organisms employ this stratagy as well, but I don’t think it qualifies as evolution.
As for what is really going on here, I don’t know. I am not familiar with this ‘cold weather fruit fly’ experiment.
I recently exchanged e-mails with someone who turned out to be a True Believer in the Institute for Creation Research (the most infamous of the so-called “Creation Science” organizations.) I coulda argued with him in the detail the topic deserved, but … I was just too tired. I gave up. And that same weekend, a friend of mine started getting on my case about how I don’t have an “open mind” for Traditional Chinese Medicine. And this was just a day after my brother’s roommates called me to tell me that he was getting evicted, and that they went through his stuff to find my number because they couldn’t get in touch with him directly, and they were all uptight about it as though the eviction were going to happen in the next 10 frickin’ minutes, and my assignment at work requires me to implement something in 3 weeks even though nobody knows what they want in it, and I’m still slogging through my attempt to debunk Wilhelm Reich and every time I get close to completing an article I discover I’ll have to write a whole nother article about some obscure thing of his that he made wild claims about, and the Red Sox still haven’t won a world series since they sold Babe Ruth to the Yankees in 1918, and sob!
As Dr. Lao indicated, the scenario I described would not be evolution as such. My heavily-veiled, disguised-so-well-as-to-seemingly-not-be-present point was just that: this appears to be an adaptation on the part of the flies, but the effect you see from one generation to the next is not evolution; certainly, no new species would be produced. At best, the second-gen flies were minor genetic variants; at worst, they were the same flies with any differences a result of development.
In not-so-subtle terms:
This is, in my possibly worthless opinion, an example of adaptation to be certain, but not evolution (beyond, of course, the fact that evolution produced the adaptation).
Or maybe white and grey moths were reproduced the same regardless of the situation but only the grey moths survived and were seen, but when it switched back the grey moths stopped surviving as well.
It’s become clear to cutting-edge evolutionary theorists that the tendency toward adaptations permitting the survival of species and individuals is merely a byproduct of the real force behind evolution; survival of genes.
I found the paper I was referring to. It’s entitled “Adaptive Mutation: The Uses of Adversity.” You can find it in Annual Reviews of Microbiology 1993, 47:467-504. As you can see, it’s quite long, but the gist of it is that some species of bacteria seem to have the ability to not only increase the overall mutation rate in response to stresses, but specifically the mutation rates of genes that will help them respond to the specific stress they’re encountering.
