But I want to focus on a couple of things that Pennisi says in her article. There has also been a discussion on Panda's Thunb: Lenski’s experiment: 25 years and 58,000 generations. Pennisi writes ...
Lenski's humble E. coli have shown, among other things, how multiple small mutations can prepare the ground for a major change; how new species can arise and diverge; and that Gould was mistaken when he claimed that, given a second chance, evolution would likely take a completely different course. Most recently, the colonies have demonstrated that, contrary to what many biologists thought, evolution never comes to a stop, even in an unchanging environment.Let's talk about two issues in that paragraph.
Stephen Jay Gould wrote an excellent book on the Burgess shale back in 1989 (Wonderful Life).1 The title refers to a movie with a similar name (It's a Wonderful Life). In the movie, George Bailey, played by James Stewart, is taken back in time and shown how his life has changed so many other lives for the better.
In his book on the Burgess shale, Gould introduces the "tape of life" and defends the position that if we rewind the tape of life and replay it, the results will be entirely different. Gould is referring to evolution over the long term (macroevolution is his schtick) and he specifically mentions things like random extinctions, chance, and asteroid impacts. The history of life, like the history of George Bailey's life, is contingent on everything that went before and small changes can have huge impacts. (Think of the Back to the Future movies.)
Gould was not referring to stepping back just a few generation and seeing if the same one or two mutations could happen again. That's not at all what he meant.
So, Elizabeth Pennisi is not being fair when she says, "Gould was mistaken when he claimed that, given a second chance, evolution would likely take a completely different course." She probably never read Wonderful Life so she doesn't understand what Gould actually said. Evolution seems to be some sort of mysterious dark matter to Elizabeth Pennisi.
In Lenski's long-term experiment, one (and only one) of the cultures evolved the ability to utilize the small amount of citrate in the medium. This gave that culture an enormous advantage. The other eleven cultures failed to evolve in this direction. I'll post a description of what happened but the evidence is clear. In order to evolve the ability to utilize citrate a number of improbable mutations had to arise in the correct order. The end result was contingent on chance events. It's pretty good confirmation of Gould's point about the tape of life [see Lenski's long-term evolution experiment: the evolution of bacteria that can use citrate as a carbon source].
And that conclusion is the exact opposite of what Pennisi says. Isn't that strange?
Biologists thought that evolution could stop
Elizabeth Pennisi says that, "contrary to what many biologists thought, evolution never comes to a stop, even in an unchanging environment." She claims that biologists (some? many?) thought that evolution would come to a stop in an unchanging environment. If they thought that, then they would have to believe two things.
- There's no such thing as random genetic drift or that fixation of deleterious alleles or nearly neutral alleles by random genetic drift doesn't count as evolution.
- Most species are perfectly adapted to their present environment so that further adaptation is no longer possible. You have to believe this because new mutations are happening all the time and if evolution by natural selection has stopped then none of these new mutations can be beneficial.
However, what she says is unfair because that's not what evolutionary biologists think. Surely there aren't many evolutionary biologists who just learned about random genetic drift from reading Lenski's papers? Surely there aren't many evolutionary biologists who thought that E. coli was perfectly adapted to growth in minimal medium?
Once again, Pennisi is conveying false and misleading information to her readers. Lenski is not stupid. When he started his experiment 25 years ago he fully expected to see evolution and when the first papers were published they did not come as a great shock to evolutionary biologists in spite of what Elizabeth Pennisi would have you believe.
Is it true that many biologists don't know enough about evolution to realize that it occurs in an unchanging environment?2 I suspect it might be true. I also suspect it's a common belief among members of the general public because that's the way evolution is usually taught. I suspect it's what Elizabeth Pennisi believed.
What does the future hold?
Richard ("Rich") Lenski has a blog. Here's what he recently wrote [Fifty-Thousand Squared],
Both of these have got me thinking about the long-term fate of this long-term experiment. Should the experiment continue? For how long should it continue? Who will take it over when (or before) I retire? And after that person retires, then what? How will they sustain it? Will they rely on the usual competitive grants? Would an endowment be more suitable? How does one raise an endowmentIf the USA can afford to spend enormous amounts of money on physics experiments and huge sums on NASA, then why not spend a few million on an endowment to make sure Lenski's long-term evolution experiment continues far into the future?
1. I'm not interested in quibbling about things that Gould got wrong in his book or about Conway Morris and his silly ideas about convergence. Save that for another day. The point here is whether Pennisi was fair.
2. Please, let's not get dragged into a lengthy discussion about stasis and punctuated equilibria. What Eldredge and Gould showed was that morphological change could be locked in by speciation (cladogenesis). In most cases, the speciation event occurred in the same environment and both species continued to exist side-by-side for millions of yeas. Neither Eldredge nor Gould ever believed that no evolution was occurring during periods of stasis.