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Observing Evolution Over 40,000 Generations
Last year we discussed the work of Richard Lenski, who has been breeding E. coli for 21 years in a laboratory in Michigan. Then, the news was that Lenski's lab had caught direct, reproducible evidence of a genetic mutation with functional consequences for an organism. Now Lenski's lab has published in Nature a major study comparing adaptive and random genetic changes in 40,000 generations of E. coli (abstract here). "Early changes in the bacteria appeared to be largely adaptive, helping them be more successful in their environment. 'The genome was evolving along at a surprisingly constant rate, even as the adaptation of the bacteria slowed down,' [Lenski] noted. 'But then suddenly the mutation rate jumped way up, and a new dynamic relationship was established.' By generation 20,000, for example, the group found that some 45 genetic mutations had occurred, but 6,000 generations later a genetic mutation in the metabolism arose and sparked a rapid increase in the number of mutations so that by generation 40,000, some 653 mutations had occurred. Unlike the earlier changes, many of these later mutations appeared to be more random and neutral. The long-awaited findings show that calculating rates and types of evolutionary change may be even more difficult to do without a rich data set."
god did it
653 mutations? 1305 missing gaps! Proof of god! Hallelulja!
I don't think you shouldn't participate in any discussions about evolution until you acquire some elementary biology knowledge.
Analogies don't equal equalities, they are merely somewhat analogous.
Yes. You are missing the fact that this experiment has been running for the last 20+ years. Time is the major factor here. Furthermore, they did a bit more than simply comparing the DNA from the current strain to the original strain. THey kept samples of strains of the bacteria every 500 generations or so and compared them. Even running parallel experiments using these stored strains allowing them to effectively repeat the experiment in order to understand the evolution of the new metabolic pathway allowing for the utilisation of Citrate.
Sigs are too short to say anything truly profound so read the above post instead.
A main purpose of the study is to investigate evolution of phenotypes, not just genomes--- i.e. how the functions and capabilities of bacteria change over generations due to evolution. Just showing there was a change in the genetic sequence doesn't do that, since it might be a change that isn't expressed.
10 PRINT CHR$(205.5+RND(1)); : GOTO 10
They already demonstrated the E.Coli bacterium evolving the ability to metabolize citric acid... that makes it a new kid of bacterium (the inability of E.Coli to metabolize citric acid is one of its defining characteristics).
-Bill
This is the same Richard Lenski whom Conservapedia (the right-wing Christian alternative to Wikipedia because Wikipedia is evil) repeatedly attacked. Apparently his work is such strong evidence of evolution, that Conservapedia's response was to more or less accuse him of faking the data. See http://scienceblogs.com/pharyngula/2008/06/lenski_gives_conservapdia_a_le.php.
ALL mutations are random. If they are advantageous, great, than it is likely that they will be passed along.
"Look, I believe in evolution, but never has there been found a parent species to something alive today. In other words, scientists can not point at any two distinct species, living or extinct, plant or animal, and say that this species evolved directly from that one."
Of course not. That's kind of like pointing to two leaves on a tree and saying one leaf came from the other. It doesn't work that way. They are both on the terminations of the branches, and the node where they branched into two is in the past. Ordinarily, the common ancestor is long dead. The nice thing with these E. coli is that the researchers kept a portion of the ancestral population intact, and the specimens are clones, so while not the actual ancestor of the lineage that kept going, they are genetically identical.
There are plenty of fossils that are close to branch points, and as more fossils are found there are still plenty of gaps left, as there always will be, but the changes necessary to span those gaps get smaller and smaller as the sampling improves. For example, Anchiornis was just discovered in the last couple of years, and a new specimen described a few weeks ago. Dinosaur? Bird? It's rather arbitrary to decide. It's either a wing-clawed, long-tailed, toothed bird like no modern bird, or it is a flight-feathered, gliding dinosaur. As if they were the leaves on a tree, birds and reptiles look distinct now, but follow the branches back far enough and they get mighty blurred together. This is hardly an isolated example.
There are fish that look so tetrapod-like that when the skull was initially found separately they thought it was a tetrapod. Then workers found the rest of the body and realized it was a fish. There are other tetrapod-like fish, such as Tiktaalik . But go back 100 years and these species weren't known at all.
I really don't know what more skeptics are expecting. Perfection? It won't happen. It's not like we'll ever have every twig on the tree. Good fossils are rare. But the statistical pattern with increased sampling is quite robust.
Congratulations! You've just described the process of evolution.
This is not entirely true, E. Coli is known to be able to metabolise glucose. The bacteria were "grown" in a solution that included glucose as it's main component. There were also many populations of the bacteria that were being evolved seperately (they NEVER mixed). Suddenly, in one population, a bacteria emerged that could metabolise citrate. This gave that bacteria a massive advantage, because it could now consume two types of food and it had no competition for the citrate (unlike glucose, which all the other bacteria could consume as well).
This also allowed the total population in that group to explode (there's now more food in total, glucose + citrate).
Another cool thing is that this smashes the "Irreducible Complexity" argument. The ability to metabolise citrate is developed by two separate mutations, which, on their own achieve nothing. Some of the populations developed the first mutation and some developed the second one, but none of them had previously developed both. This shows that the "preliminary" mutations were not harmful to the bacteria, so they just "hung around" until one of them was lucky enough to get the second mutation too.
Anyway, look up Lenski's work, I'm sure his papers (and those of his students/colleagues) are better at explaining it all than me...
1178161 is prime...
Sorry, they're saving the next Nobel Prize in Medicine for Obama...
Lawrence Person (lawrencepersonh@gmailh.com (remove all "h"s to mail)
http://www.lawrenceperson.com/
The standard method of identification of bacterial species is to determine what compounds they can eat. E. coli is defined as not being able to eat citrate. They evolved something from E. coli which can eat citrate. The new bacteria is not E. coli by the standard method of identification.
But I guess you're right... it's still just some random nigh-invisible animalcule that nobody really cares about. I mean it didn't turn into a dolphin, did it?
Explain crocodiles. According to the fossil record they have hardly changed from their ancestors millions of years ago. But they *have* changed. And we don't "only find the dead end". There is no dead end if there are descendants. What you're forgetting is that fossilisation only happens in relatively rare circumstances, so the vast majority of the record is not preserved at all. That unfortunately is where the step by step evolution would be easily recognised. But you can still fill in the gaps with insight and close examination. After all, the current generation came from somewhere, and it's pretty unlikely it started from scratch as is.
Regarding crocodiles, the current species get to between 20 and 30 feet in length. Crocs in the Cretaceous period were around 40 feet in length. But back then they were dealing with prey much larger than is available today. Overall, most species on earth are smaller than their ancestors, except of course humans, who have no real predators and are able to take advantage of a wider range of foods.
We have played our part in the destruction of the chain of evidence too. If you buy fish, you may have seen a halibut on the counter. Maybe it's a couple of feet long, probably less. But specimens have been caught that are 7.5 feet long and weigh over 621 pounds. They only get that big through long life, and these days we are catching them before they ever get that big. Future paleontologists will wonder why the "giant halibut" died out relatively suddenly, but there will be no missing link fossils because we ate them.