Posted on 06/17/2003 7:05:07 PM PDT by Pharmboy
H. E. Hoekstra
Evolution has allowed some rock pocket mice,
pictured on light and dark rocks, to produce
distinct fur that helps disguise them.
In the deserts of the Southwest, among the towering saguaros and the spiny cholla cactuses, rock pocket mice hop and dash in search of a meal of seeds. But while these mice may seem to scamper haphazardly across the desert floor, their arrangement in nature is strikingly orderly.
Nearly everywhere these mice are sandy-colored, well camouflaged as they scurry across beige-colored outcrops. But in some areas, ancient lava flows have left behind swaths of blackened rock. There the same species of rock pocket mouse has only dark coats, having evolved an entirely distinct and, for their surroundings, equally well-disguised pelage.
Now, in a recent study in The Proceedings of the National Academy of Sciences, researchers report identifying the gene responsible for the evolution of dark coat coloration in these mice, pinpointing the DNA sequence changes that underlie this classic story of evolutionary change, the cute and furry counterpart to the famous case of the peppered moth.
Researchers say the study is the first documentation of the genetic changes underlying an adaptive change where the evolutionary forces were natural. Scientists point out that other well-known cases involve evolution caused by humans; some have suggested that those changes may be atypical of natural evolutionary change, since they have typically involved intense, directed pressures destroying most of a population, like the spraying of pesticides or the application of antibiotics.
"This work is very important," said Dr. Mike Majerus, an evolutionary geneticist at Cambridge University, who was not part of the study. "Here man is just not involved. The sandy and lava flow substrates are entirely natural phenomena."
Other well-studied examples of human-driven adaptive change include the evolution of pesticide resistance in insects after widespread spraying and the increase in the numbers of dark-winged forms compared with light-winged forms of the peppered moth in the United States and England after industrialization turned air sooty and polluted.
Dr. Michael W. Nachman, a population geneticist, along with colleagues at the University of Arizona, Dr. Hopi E. Hoekstra and Susan L. D'Agostino, studied mice living on Arizona's Pinacate lava flow in Arizona and on light-colored rocks nearby. The researchers were able to take advantage of decades of meticulous work in which other scientists identified some 80 genes that affected coat color in laboratory mice.
On close examination, the light-colored rock pocket mice could be seen to have a type of hair coloration similar to standard, sandy-colored laboratory mice. In this pattern, known as agouti, the hair is black at the base, yellow in the middle and black again at the tip. The dark-colored rock pocket mice had completely dark hairs.
Researchers knew that mutations in a few well-known coat coloration genes in laboratory mice could cause such complete darkening of the hair, and they began by looking at two genes known as agouti and Mc1r. When they looked at DNA sequences in light and dark mice, changes in the agouti gene did not appear to be associated with light-colored fur versus dark-colored. Still, the researchers found that a certain cluster of mutations at Mc1r could be found in every dark-colored mouse.
"It's a textbook story," Dr. Nachman said. "Now we have all the pieces of the puzzle together in a natural setting."
Dr. Nachman noted that while the new study points to the Mc1r gene as the key to turning mice dark on the Pinacate lava flow, the team also found that dark mice on another lava flow in New Mexico did not share those mutations.
"So the same dark color has evolved independently in the two different populations," he said, "through different genetic solutions to the same evolutionary problem." Dr. Nachman said changes in another gene, perhaps the agouti gene, could be responsible for dark coloration in the New Mexico's Pedro Armendaris lava flow.
One could easily imagine that coloration would be of no consequence to the rock pocket mice, as they are nocturnal, darting about under the desert night sky. But researchers, working early in the last century, released light and dark mice on light and dark backgrounds in an enclosure at night and found that owls, a major predator of mice, could easily spot a mouse on a mismatched background.
Dr. Nachman noted, however, that these early researchers did not use rock pocket mice in their study, but instead used a species in which the dark and light forms were actually much less distinct.
As a result, he said, "we think the owls are discriminating even more strongly in our species." He said tiny bits of rock pocket mouse were often found in pellets at owl roosts.
Dr. Majerus said many kinds of animals showed light and dark forms, from deer mice to squirrels and chipmunks. There are even black ladybugs.
"A lot of the dark forms show an association with a particular type of substrate they're on, or the frequency of burning and charring of the trees in the woodlands," he said, noting that it would be interesting to do genetic studies in other animals, to see how many genetic solutions these other animals have come up with to turn dark.
But while many dark forms are abundant and can be studied at scientists' leisure, Dr. Majerus said that of the peppered moth was slowly disappearing.
So while there is nearly unanimous praise for the increasingly clean air in industrialized regions of the United States and Britain, there may be, at least for some scientists, a downside. "We've got about 15 or 16 years," Dr. Majerus said, "before those black forms, if they continue to disappear at the current rate, disappear completely."
I hereby abandon thread.
BTW, PH, I just finished a late 19th century bio of your namesake. A great man for sure -- a liberal mind, a devout Christian, and a man of action.
Careful, somewhere some creationist quote-miner is yelling, "Score!"
But without a foil, ALS and bondserv wouldn't be posting and showing the lurkers what the Real Science has to offer for next year's biology class. OK, the bad news is that the thread gets polluted with reams of utter drivel.
The "surprise" to me, if any, is that fact that you are yet comfortable enough with roust-a-bout Debate to still tolerate the current atmosphere of Free Republic. As I said, I don't spend as much time here as I used to. The intellectual... atmosphere... has declined, in my elitist and insufferably-arrogant opinion.
I think your opinions are idiotic. You think the same of mine. I'm prepared to say so, and so are you... So be it!! But these days, it seems to me as if the simpering sycophants infesting this Forum have an obnoxious tendency to take things personally... especially if one questions the Dagon-God of modern "compassionate conservatism". This place just isn't as smart as it used to be. And it's a lot more hyper-sensitive.
You're a throw-back to the old days, Vade. A Dinosaur in your own time. "Sticks and Stones may break your bones, but Words will never hurt you." Ahh, for times gone by. It's not the same anymore (JMHO).
This is not particular to rats becoming bats, which is just as well since rats and bats are not particularly related. (Rodents are not postulated as ancestral to bats.) Doc is making an argument that you can't get from A to C because B in between is neither fully A nor fully C and thus useless. However, "useless" does not follow from "being between A and C."
For the record, Confusiornis is even rather less related to the entire Class Mammalia, given that this species belongs to Class Aves.
So what your Kentucky Fried Hoatzin has to do with Bats, is still beyond me.
Gee! Somehow you missed that what a dinosaur can do, a tree-dwelling insectivore mammal can do.
Well, other than the fact that you are hop-scotching across entire Phylogenetic Class Boundaries and an (alleged) 100 Million years of evolutionary time...
The Confusiornis is still a Bird. Still a second-cousin-twice-removed of the South American Hoatzin, NOT AN IGUANA. Just as the Duck-Billed Platypus is phylogenetically closer to an Otter than it is to a Duck.
So what the Confusiornis has to do with Bats is not only beyond my Ken, its relation to the development of Flight and Sonar among Bats remains more the province of a creative writing class, than anything remotely related to Science.
And being lightweight is already useful in an arboreal species which may have to crawl far out on the ends of branches, and maybe leap or glide from there. Here, for instance is a gliding lemur which has independently evolved a lot of bat-like characteristics without being a bat.
You'll forgive me if I explain to you that Flying Squirrels are not, in fact, Bats. Shocking, isn't it. And as to "independently evolved" -- show me, don't tell me.
At the point that you have a BAT on the one hand, and a FLYING SQUIRREL (etc.) on the other... you have a Bat and a Flying Squirrel (or Lemur). Have you any evidence whatsoever for Evolution? No, you have merely assumed evolution.
That which could just as well be the Intelligent Design of two different mechanisms (Flying and Gliding), and which shows up in the fossil record as two different mechanisms (Flying and Gliding), does not prove Macro-Evolutionary progression. You have only assumed as much.
I also notice you've ignored the rest of my post, a considerable body of material refuting the very essence of your spastically flailing arguments. This of course allows you to reappear dumb as a stump tomorrow, trolling for suckers.
I thought the latter half of your Post was burdened by the same assumptions as the former half. Lots of Assertions, little Argument.
If you think I missed anything Relevant, please bring it to my attention.
Altogether, It seemed pretty irrelevant to me.
Best, OP
Well, I am, unfortunately, a connoisseur of Excess -- probably all too often (I am trying to slow down, for my own good). I always aim to "push the envelope" -- intellectually most of all.
But you mistake my argument. I am not saying that a Life-Span extending mutation is harmful in principle. I am saying that Demographic Burdens must be taken into account.
Since you seem to be misunderstanding my argument, let's apply a good reductio ad absurdum to make the point. Let's say that some sort of "human genetic mutation" vastly extended the period of human physical deterioration after age 60, from an average of 15 or 20 years to an average of 300 years. An average of 360 years of life, but no increase in physical capability after age 60 -- just a vast extension of the "deterioration period" after age 60.
Pretty soon, the Human Race is burdened under a Dependency/Support Ratio of at least 5-to-1. FIVE non-working, non-reproducing indigent dependents for every Productive Worker, even defining "productive work" as ages 0 through 60 (which includes Child Labor).
Soon enough, you have a Race which is so burdened by its support of the elderly indigent, that it can't afford to support Offspring -- not even in terms of Socialism or Capitalism, though Socialism exacerbates the problem, but simply in terms of available work-energy.
In other words, a Race which is marked for Extinction, in terms of its own Replacement Ratio. It's interesting that you bring up the APO-AIM variation in regards to Italy, in particular... you're illustrating my point. Italy has the lowest child-birth rate of any European Nation besides Spain -- and therefore, the deepest Population Deficit in terms of their Replacement Ratio. The Italian birth-rate is in the neighborhood of 1.2, when they need at least 2.1 just to maintain their population.
Any additional increase in Population Life-Span WORSENS the Demographic Dependency-Support Ratio.
Here's the scoop -- even assuming that the APO-AIM variation extends average Life-Span among southern Italians, you are just PRESUMING that this is a "beneficial mutation". BUT IT ISN'T. Not in the Darwinian sense. By exacerbating the Dependency-Support Ratio, by increasing the number of elderly indigents requiring Care and therefore reducing the available work-energy available for new Offspring.
In the Darwinian sense, by exacerbating the Dependency-Support Ratio among Southern Italians (who, in terms of work-energy, need additional Offspring and simply cannot afford elderly indigents), this is not a "beneficial mutation" at all -- you are accelerating their Extinction.
In a strictly-Darwinian sense, there is no possible way to consider such a "mutation" as beneficial in the light of current Demographics.
Glorify God in your Work, and WORK TILL YOU DIE. Retirement? We don't need no steenkin' "retirement".
But aside from Calvinist Populations, the Dependency-Support ratio is a serious demographic consideration in most Human social groupings.
I disagree that a fully capitalist society (one not burdened by today's gov't. style Social Security & Medicare) would not be able to support 300-year old senior citizens. In a fully free market society most 300-year old retirees would be living sustainably off 401K's that have been growing more or less steadily for 270 years!
TTFN
You might rather one or the other (eating salads till age 90, or Big Macs till age 75), but in purely-cynical terms, Europe doesn't need either. It needs old people to Die Off, and rather quickly.
When the Birth Rate falls below the Replacemant Ratio, any addition to the Life-Span (aside from a "Work till you die" Calvinist Ethic) exacerbates the Dependency/Support Ratio.
"Beneficial" Mutations ain't beneficial, in such a case. Life-Span enhancement only accelarates racial extinction.
(BTW, I agree with the concept of working 'till you die. Or at least, being productive 'till you die. :-) I disagree that a fully capitalist society (one not burdened by today's gov't. style Social Security & Medicare) would not be able to support 300-year old senior citizens. In a fully free market society most 300-year old retirees would be living sustainably off 401K's that have been growing more or less steadily for 270 years! TTFN
Well, if you ain't breeding, it's still genetically moot anyways.
But if one permits a momentary intrusion of Realism (Libertarians are permitted to be Organically Realist; hail Rothbard!!) -- every society in human history, rich or poor, requires Parental Work-Energy to provide for children. You can't very well breast-feed an infant on T-Bills, or let the Mutual Funds read Junior a bed-time story. It's just not gonna be the same.
It's not even a question of Wealth, it's a question of available Work-Energy.
And if you are proposing that the indigent elderly shall become economically-independent of worker-support... show me, don't tell me. As I said, Libertarians are permitted to be Organically Realist; hail Rothbard. Just give me one example, anywhere in history.
Or just say, "I'm less realistic than the Creationists!! I'm basically a Utopian!! Anyone gotta Brooklyn Bridge to sell me??"
Gee! Imagine that! You still don't understand, even though I told you exactly what it has to do with bat evolution. It demolishes the particular eyes-jammed-shut thought-experiment that you can't have a wing that's only halfway a wing and halfway something else. The_doc clearly and unambiguously made exactly that argument. It's a perfectly ridiculous example of creationist science in action and I demolished it with one picture of one fossil.
Granted, bats have a lousy fossil record. This may mean no more than that much of their evolution took place in an upland forested environment which is very unlikely to have left any fossils at all. When you look at the fossil record, you see mainly lowland/tidal swamps, sea bottoms, lake bottoms, and maybe a lowland river floodplain. Other topographies, especially the more raised ones, tend to wash away over time. They have essentially no fossil record. The mountains where I live have been eroding since before the Permian-Triassic extinction. That's what mountains do. They wear down.
That's a big gap in the fossil record between the topsoil layer and the first solid rock. There is no fossil-record proof that anything lived here between the time when salamanders ruled the earth and the Indians dropped a few stone arrowheads, but it's ridiculous to suppose that nothing did.
The absence of early bats only means something if you buy the creo nonsense that all absence of evidence is evidence of absence. (Especially when you consider that the fossil record of practically everything else is so much better. You're basically like the old High School bully at the 20th class reunion picking on the only guy left who hasn't bulked up bigger than he is.) If you were going to be consistent about that, the finding of a new fossil to fill a gap would prove something to the gap-gamers. Presence of evidence should be evidence of presence (or the absence of absence, whatever).
But the finding of a new fossil never proves anything to the gap-gamers. What does that tell us? For them, it's clearly not about the actual content of the fossil record at all.
When Darwin first wondered where all the missing links were (and skeptics took up the mocking chant), he was boldly predicting that the very sketchy evidence of his day would be fleshed out further. He said that some kind of Precambrian life would turn up, some kind of link from land animals to whales would surface, some kind of link from apes to man would be found in the fossil record, some kind of link from dinosaurs to birds was likely ...
So was he the luckiest charlatan of the 19th century or what? The actual track record is better than what I outline above. Compare this link to the teats-on-boar-hog "God could have done that" one-answer-fits-everything retrodiction of creation "science."
Note the difference between saying that bats have no fossil record and that bats cannot have evolved. Note the difference between rejecting something on an intellectually honest basis and bludgeoning with how many different ways you can misunderstand and mischaracterize it.
I think your opinions are idiotic. You think the same of mine.
Your opinions are understandable to me, but only in psychological and historical senses. You're stuck in the cultural heritage of an oogedy-boogedy magical past, a 21st-century witch-doctor shaking his rattle at devils and denying both science and logic. The cognitive dissonance of all the evidence against what you believe has driven you nuts. I'm fascinated by the pathology, can hardly look away.
I thought the latter half of your Post was burdened by the same assumptions as the former half. Lots of Assertions, little Argument.
I'm not going to repeat everything in every post, but I have, since your reappearance on this thread, posted to you links to a library worth of evidence that transitional fossils exist and that independent lines of evidence converge to point to evolution. You have only your ability to ignore, wish away, and mischaracterize.
Let me make sure this one is thread-level and not buried in some sub-link somewhere: 29+ Evidences for Macroevolution.
It's not even a question of Wealth, it's a question of available Work-Energy.Wait, are you trying to say that a society of near-immortals would eventually run out of people of working age (over many generations)?And if you are proposing that the indigent elderly shall become economically-independent of worker-support... show me, don't tell me. As I said, Libertarians are permitted to be Organically Realist; hail Rothbard. Just give me one example, anywhere in history.
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