Discussion of everything related to the Theory of Evolution.
It is admirable that the authors showed restraint and did not immediately declare the Cit+ population to be a "distinct" species. But it probably is a new species. Since E. coli reproduces asexually, the two populations are effectively isolated. (Even if they weren't, the Cit+ population is isolated from the other 11 cultures.) Unless the entire Cit+ population reverts back to the Cit- genotype, it is a new species. In other words, we now have two kinds of bacteria that differ in both genotype and phenotype and descended from a common ancestor.
I'm not sure what point you are trying to make here. Historical contingency is a proposed mechanism of Darwinian evolution. The LTEE study supports the hypothesis that historical contingency was important in this particular evolutionary change. It does not, however, establish that historical contingency plays an important role in evolution generally. But even if the importance of historical contingency does become established, that would not falsify Darwinian theory; it would reveal in greater detail how Darwinian evolution works.
I would not use the term "proven." Darwinian theory (or more precisely, neo-Darwinian theory) is one of the most well-confirmed theories in science and thus ought ot be taught in science classes. Evolution, on the other hand, is a fact. Even before Darwin, scientists recognized that organisms change over time. They just didn't know how it occurred.
My take on these numbers is just the opposite of yours. The first bacteria on Earth that could exploit an abundant energy source would have undergone explosive growth, since there would have been no competitors. Within a short time, the numbers of these bacteria would have dwarfed the number in the LTEE's 12 small cultures. If the LTEE shows evolutionary change in 30,000 or 50,000 generations, I would expect such changes to have occurred much more rapidly in the much larger population that probably existed billions of years ago -- or for that matter in the larger natural populations that exist today.
It is also a mistake to generalize from the mutation rate in the LTEE, because mutation rates vary greatly. My evolution textbook has a table showing various mutation rates per 100,000 cells or gametes. These range from 0.00004 for streptomycin resistence in E. coli to 12 for yellow body in fruit flies and 4.2-14.3 for achondroplasia in humans. (Source: Evolution by Douglas J. Futuyma, 2005, Sinauer Associates, p. 171)
Last edited by StevePush on Thu Oct 21, 2010 6:21 pm, edited 4 times in total.
I wouldn't argue with you regarding the exchange of genetic information in real life. You have the real life experience, I don't.
I can only refer to the papers by biologists themselves.
Why Lenski has not sought out a real life environment, only he can answer. I expect it has to do with control of the process.
My experience has shown me that peoples' views are most often sincerely held. So although they may not be in accord with the facts I feel that the people holding them should be treated with respect. It can sometimes be very frustrating though.
The main objective of the cited article is indeed an investigation of hybrid sterility among subspecies of Drosophila paulistorum. This topic is interesting because it elucidates an important aspect of speciation: Sexually reproducing species must be reproductively isolated.
The evidence you seek is mentioned only briefly in this paper. On page 152 the investigators wrote, "The Guianan [group of Drosophila paulistorum populations] is the most distinctive, and seems to deserve being regarded a species of its own." A year later the researchers published another paper documenting why the Guianan subspecies had evolved enough to be regarded as a separate species, which they called Drosophila pavlovskiana. I have not been able to find this paper free on the Web, but the first page, including the abstract, is available at http://www.jstor.org/pss/2423385
According to the Encyclopedia of Life (http://www.eol.org), Drosophila pavlovskiana is still recognized as a separate species.
There is quite a lot of data available on Horizontal genetic transfer (HGT), as it is known in bacteria. I encourage you to look at it. The evidence of genetic instability are there.
The main problem is that we know very little of the life of bacteria outside of the lab. take a gram of soils, and you will be able to identify 1000's of bacterial species. But bacteria can acquire DNA from dead cells (whatever they were) or from phages, which are estimated to be 10x more numerous than bacteria. Moreover the ability of bacteria to pick-up foreign DNA and to keep it is directly dependent of the environment. So the LTEE is a reductionistic view of what is happening in real life. Lenski has made the choice to observe what happens to isolated populations of E. coli if left for thousands of generation. It is a good way to estimate the importance of accumulation of point mutations. He is dong his analysis of his strains and point to the things that he finds interesting. As I have mentioned earlier, others have had a look at his strains and have demonstrated some interesting side effects, notably re speciation, something that Lenski seems not to have seen worth pursuing. But it is only a very tiny ray of light in the immensely complex unknown that bacterial communities are representing. Taking this experiment as a benchmark to estimate the rate of evolution in the real world is quite frankly foolish.
Maybe you could have a look at some of the work by (for example) Ivan Matic, François Taddei, Miroslav Radman and Erick Denamur on the mutator phenotype.
Science has proof without any certainty. Creationists have certainty without
any proof. (Ashley Montague)
You raise the real life scenario and quite rightly so, but what is this real life scenario demonstrating.
HGT is a major factor here. However what does it say about one of the central doctrines of Darwinism, Common Descent.
It took Carl Woese decades to have his views of a separate domain of Archaea accepted.
Why such resistance?
One of the reasons was that it contradicted the Darwinian view of common descent, a single tree of life, the simple illustration so often depicted in textbooks. This was one of the early things I was taught in biology class at college.
Ofcourse there is no single TOL. It’s now beginning to be regarded as more of a bush - I would argue as more of a forest. And you rightly point to the importance of HGT that is so prominent in this regard.
Also you quite rightly point out that the Lenski experiment is a good way to estimate the importance of accumulation of point mutations. But what has he discovered about these point mutations?
Well let him answer. ( Please note carefully)
“..each population tried every typical one-step mutation many times.”
So even in this most highly selective environment point mutations with or without historical contingency, the simple variation in a trait requires literally hundreds of thousands of generations. So as I asked previously how many generations would be required for a full digestive tract to be produced.
Now you rightly say to use this experiment, as a benchmark to estimate the rate of evolution is frankly foolish. I would say it is frankly ridiculous. There is no way to use this as a benchmark for something that isn’t happening.
Please bear in mind why this even modest change is so difficult - because of the rigid control the cell exercises during division. Clearly the cell legislates against random changes or biological noise as a communications engineer would describe it.
So in the wild we see the role of HGT (at the very least) compromising the idea of common descent.
In the lab we are getting direct evidence on the very weakness of point mutations to drive speciation.
That leaves natural selection, and Darwin himself acknowledged that NS is not the only mechanism to speciation. Natural selection can eliminate a species that is not adapted to it’s environment but it has no power to modify it’s form. It can only work on what is already there.
So of the three fundamental pillars of Darwinism , random variation/mutation, natural selection and common descent, I see only, possibly one third of one pillar that has potential.
In 1999 Ernst Mayr (one of the founding fathers of the modern synthesis) received the Crafoord Prize from the Royal Swedish Academy of Science and gave a lecture, and which in part he said
He goes on
I am arguing against a philosophy, not science and I have no less an authority than Ernst Mayr himself promoting that view and with pride.
All I ask is not to confuse philosophy with empirical science. This confusion is all too apparent in, for instance Jerry Coyne’s book “Why evolution is true” that Steve referred to and I would be only too happy to discuss it, to demonstrate my point.
It says that in addition to the genes of their immediate ancestors, organisms sometimes carry genes form other branches of the tree of life. Recent genetic analysis suggests that all life descended from a single ancestral gene pool.
It took more than a century for the Copernican model of the universe to be accepted. New discoveries sometimes take awhile to gain widespread acceptance. Usually this is for good reasons (e.g., not enough data yet).
Woese didn't challenge the tree; he rearranged it.
None of those metaphors is perfect.
What digestive tract? Human? Probably on the order of tens to hundreds of millions of generations. Along the way, more primitive digestive tracts evolved in fewer generations.
If you believe evolution does not occur, what alternative do you support?
Yes, cells repair DNA damage, deactivate viral genes, etc. Despite these mechanisms, genetic variation is an empirical fact.
You have misinterpreted the Mayr quote. He was speaking of the "philosophy of biology," that is the branch of phiosophy that studies how biology is done. He was not saying that biology is unscientific. It is, in fact, as rigorous as any other field of science.
I'm unaware of an experiment that provides empirical support for macro-evolution above the species level. However, there are claims of new species produced from existing ones. With much debate over the meaning of the word "species" and over methods of species identification, its difficult to find consensus on the matter. Its possible that some of these "new species" may simply be variations within the species itself. In other cases, it appears the new species are a type of hybrid limited by reproductive postzygotic barriers.
i think that it is very informative for you and you also find the your answers in this paragraph..
Sperm competition, when sperm from different males compete to fertilize a female's ova, is a widespread and fundamental force in the evolution of animal reproduction. The earliest prediction of sperm competition theory was that sperm competition selected for the evolution of numerous, tiny sperm, and that this force maintained anisogamy . Here, we empirically test this prediction directly by using selective breeding to generate controlled and independent variance in sperm size and number traits in the cricket Gryllus bimaculatus. We find that sperm size and number are male specific and vary independently and significantly. We can therefore noninvasively screen individuals and then run sperm competition experiments between males that differ specifically in sperm size and number traits. Paternity success across 77 two-male sperm competitions (each running over 30-day oviposition periods) shows that males producing both relatively small sperm and relatively numerous sperm win competitions for fertilization. Decreased sperm size and increased sperm number both independently predicted sperm precedence. Our findings provide direct experimental support for the theory that sperm competition selects for maximal numbers of miniaturized sperm. However, our study does not explain why G. bimaculatus sperm length persists naturally at ∼1 mm; we discuss possibilities for this sperm size maintenance.
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