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.
As an agnostic on macro-evolution (lizards changing into bunny rabbits) I'm not too impressed. However, as one who recognizes the existence of small changes (one type of fly becoming another type of fly), it was a well-done experiment. Kudos to the experimenters.
I'm a scientist who believes that God created the universe. If He chose to use evolution then that's fine by me. I know the Who and Why behind the universe but agree that it takes science to discover the How. Evolution neither proves nor disproves the existence of God, and vice versa.
Other responses which are anticipated from the denial crowd:
- It's a designed experiment. That proves ID!
- It's a lie!
- It hasn't speciated yet!
- Blasphemy!
- They're interpreting it through their naturalistic worldview.
- How dare you use the screen name "Patrick Henry"?
- Yeah, but "get your own dirt!"
Let me know if you wish to be added or removed from this list.
I don't get offended if you want to be removed.
Techniclly, I dont think this is true. From the text:
...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 proved that a small genetic change (somehow occurring, either by direct intervenion or perhaps by random mutation) will change the characteristics within a species. As far as I can tell, they may still interbreed. Even the scientists hedge by saying they have seen the first step in the proces of speciation only. Progress indeed. But for it to lead somewhere, they need to prove that eventually they can create different species altogether (i.e. unable to interbreed).
Exactly right! Well said.
I don't remember Darwin mentioning a gene splicing machine in his theory.
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