Posted on 12/09/2003 7:47:21 AM PST by PatrickHenry
In what has been described as the "perfect experiment," evolutionary biologists at the University of Chicago replaced a single gene in fruit flies and discovered a mechanism by which two different "races" begin to become different species, with one group adapted to life in the tropics and the other suited to cooler climates. The tropical group was more tolerant of starvation but less tolerant of cold. The temperate group was less able to resist starvation but better adapted to cool weather.
The altered gene also changed the flies' pheromones, chemical signals that influence mating behavior. As a result, the researchers show in the Dec. 5 issue of Science, the two groups of flies are not only fit for different environments but may also be on their way to sexual isolation, a crucial divide in the emergence of a new species.
"This study directly connects genetics with evolution," said Chung-I Wu, Ph.D., professor and chairman of ecology and evolution at the University of Chicago and director of the study. For the first time, we were able to demonstrate the vast importance in an evolutionary context of a small genetic change that has already occurred in nature."
"We had the luxury," added co-author Tony Greenberg, Ph.D., a postdoctoral student in Wu's laboratory, "of watching the essential event in Darwinian evolution, the first step in the origin of a new species. We were quite impressed, that this simple alteration played such a dramatic role, both adapting flies to a new environment and changing their sex appeal. Once two groups become sexually isolated, there's no turning back."
The scientists used a new technique to knock out one gene from fruit flies and then replace it with one of two slightly different versions of the same gene.
They focused on a gene called desaturase2 that plays a role in fat metabolism. Flies from Africa and the Caribbean, where there is tremendous competition for food but cold temperatures are not a problem, have one version of ds2. Flies from cooler climates, where there is less competition for food but greater temperature variation, have a smaller, inactive version of ds2.
The same gene plays a role in the production of cuticular hydrocarbons -- waxy, aromatic compounds that coat the abdomen of female flies. A male fly, in a romantic mood, strokes the female's abdomen with his feet, which have sensors that recognize specific hydrocarbons, like a perfume.
In a previous report, Wu's laboratory found most males with the temperate version of the ds2 gene preferred females with the same gene; tropical males preferred tropical females.
"Developing increased cold tolerance was an important step for flies that migrated out of Africa to Europe and Asia," Wu said. The change in pheromones, which altered patterns of sexual attraction, "was a by-product of adaptation to colder weather."
Fruit flies have a migratory history similar to humans. They originated in Africa, spread to Europe and Asia and went on to populate the world. As with humans, there is greater diversity within African flies than between flies from Africa and other continents.
Although fruit flies have been a favorite model for the study of genetics since the early 20th century, recognition of consistent differences between tropical and temperate flies came only in 1995. The discovery, however, "has allowed a lot of analysis of the evolution of adaptive traits," Wu said.
"But this was the first time we have been able to study the process from the very beginning," he added, "to watch the first steps as one species begins to split into two, then seals the bargain by increasing sexual isolation. This is the essence of biodiversity."
Additional authors include Jennifer Moran from the Wu lab and Jerry Coyne of the University of Chicago. The National Institutes of Health and the National Science Foundation funded the study.
The hydrogen bomb was a helpful model. Sounds like you give up easily.
Not really: the deuterium/tritium fusion reactions in a H bomb are entirely different from the carbon/nitrogen/oxygen cycle reactions that power solar fusion.
I looked that up. Romans used a wet sponge on a stick. I take back all the favorable things I wrote about them.
No. It's true that the genetic change itself did come from an intelligent source. But we know such a change could come about through random mutation, if we observed nature for long enough (we know random mutations happen, that much is really not up for debate). But the mutation itself is not what is really interesting.
The insects themselves have chosen not to breed with each other (for the most part, at least--the article said they "preferred" their own kind). Once the scientists set the mutation in motion, the flies themselves have separated themselves out. This sexual isolation between the two groups is not the result of scientists keeping half the flies in one cage and half in the other, but is the result of choices made by individual flies.
In other words, evolution does not require top-down management from scientists or a deity. The individual actors themselves will organize into species without top-down interference.
Of course, the actual speciation has not yet happened, and that will probably take a while (it will probably be more than just a few generations before they are physically incapable of mating). Still, this experiment is pretty big news.
Bwahahahahaha! No such thing as random mutations? HAHAHAHA...
Behavioral isolation is actually very important. There are many species of birds that are physically capable of cross-breeding but seldom do, because of behavioral isolation. The most remarkable are red crossbills. Crossbills are finches that have specialized crossed beaks that they use to extract seeds from pine cones. However, a given beak size is typically optimal for only one or two species of pines. So if you have a population of large-beaked crossbills, that feed on one species, and small beaked crossbills that feed on a different species, then if they mate, the beak size will be intermediate, and the poor offspring will be inefficient at extracting seeds from either species.
So what happened is that divergent groups of crossbills adopted different songs, and female crossbills only mate with males that sing songs of the correct type. There are a total of 9 breeding groups in the US, and they seldom crossbreed, even though a birder can't distinguish any of the types by sight. These are in effect nine species.
By the way, it appears this speciation only occurred in the last 10,000 years.
This is a commonly held "objection" to the theory of evolution, and it's based on a total misunderstanding of what goes on. There is no "spontaneous speciation" in evolution (unlike in creationism.) Rather than spontaneous speciation, what happens is that one individual member of a species is very slightly mutated.
Suppose it's a long time ago, when the human population is rather small and scattered. You might, for example, be born with longer legs than most, and you might find that advantageous in running. You'd be able, however, to find a mate. Yes, it takes two to tango, Charles Darwin was aware of this, but it's no problem at this point. If you and your long-legged family become separated from the parent stock, by migrating to a new valley, in a great number of generations your whole tribe might be long-legged people who are all great runners.
Repeat this for some new mutation. And repeat again. Do this kind of thing for thousands of generations. Eventually, your tribe (or its very distant descendants) could become speciated, and unable to breed very much with descendants of the original stock, when you might some day meet up with them.
Evolution takes time. Lots of time. Little things add up over the generations.
More accurately, we can speculate that such a change could occur. The word know implies an absolute and, unless the exact mutation that this gene splicing experiment caused is actually observed occuring in nature, we don't know that it could occur. What we know can happen is only that which we have actually observed happening. Anything speculated from lab experimentation about natural processes falls into the "educated guess" category, not the "knowlege" category.
This is where the problem with evolution lies. It's all, basically, speculation. Untill life can be observed coming from non-life (etiher from a laboratory experiment or in a natural setting), evolution wil have to be considered as speculation, not as scientific fact (same with creationism or intelligent design, of course).
If you were provided with information showing exactly this [observed speciation], would it change your mind in the slightest?
You know I can't do that. That is why this recent discovery is so important--because it brings us one step closer to proving this piece of the puzzle.
There is no way with current technology that we could collect enough data on enough living creatures for a long enough time period to watch this process occur completely in the wild. The scientists have merely kickstarted the process.
What you are asking is also unreasonable because one mutation by itself will almost never cause one species to split in two. If you read the article, you'll see that this one important mutation has a trigger effect, causing two distinct subgroups of the species to form and isolate themselves from each other. Over time, as they accumulate more mutations, and the idea is that after numerous mutations they will eventually become incompatible and hence will be considered to be two distinct species.
From what I understand, mutations take place within DNA molecules, which are big, big molecules (as far as molecules go), and no portion of them is much more special than any other portion (i.e. mutations are about as likely to happen anywhere as anywhere else). That would mean a simple mutation like the one in this article would be very possible in nature.
Untill life can be observed coming from non-life
Evolutionary theory holds that creatures will evolve. It has nothing specific to say about the origins of this universe. For all we know, God created the Earth and populated it with bacteria and virii, and they evolved by themselves (with the approval but not direct interference of God). Such a possibility would allow for both evolution and God to coexist.
The idea that life could have evolved from non-life is different from the basic evolutionary theory.
That's just a variation of intelligent design or creationism. It gained a lot of popularity back in the twentieth century, even among the churches. You might add it as a third theory, not truly creationism or evolution. But the truth is that we all choose which one we believe and each choice (perhaps not the theory, but the choice) is equally valid to any other (as a choice).
The thing that strikes me is that only creationism based on a classical Judeo-Christian type of viewpoint would ever be known to be right, by those who believe it, if it is true. All the others (even the reincartionists) would simply know nothing in the end if they turned out to be right. Maybe that's why I choose to believe in creationism: If I'm right, I (and everyone else) will know it for eternity, and if it turns out I'm wrong nobody will ever know it. No downside to that that I can see.
How fast should speciation be happening naturally to account for all the species that exist in the world?
Shouldn't it have been observed at least once in a few thousand years of recorded history?
Yes. And it has:
Observed Instances of Speciation .
Some More Observed Speciation Events .
One of my favorite examples is Nylon-eating bacteria. Of course, it's not the same definition of species as applies to a eukaryote, but you have to admit, it's certainly a new biochemical pathway, and also that it would be a fatal mutation in a nylon-free environment (eg the Earth prior to the 1930s)
I have a question for you: why would you expect *one* mutation to cause speciation? Isn't it a gradual process, as the percentage of viable, fertile offspring decreases? How many mutations separate donkeys from horses? Greate Danes from chihuahuas?
An interesting almost-example involoves the rh blood factor. If the mother is rh-negative and the baby is rh-positive, and any fetal blood mixes with the mother's, she produces antibodies to it. A subsequent pregnancy with an rh-positive baby will very often result in a miscarriage. If this were symmetrical (ie an rh-positive woman carrying an rh-negative baby...) and *always* resulted in a miscarriage, the rh+ and rh- populations would be different species. (The Basques have the highest rh-negative rate in the world. I wonder if this has helped them remain a distinct population?)
Are you seriously implying that it took a miracle to make the mutation!?
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