If you read this blog, you probably read about the report in Science describing a claim that scientists had isolated a bacterium from Mono Lake in California that substitutes arsenic for phosphorus to sustain its growth. Our data show evidence for arsenate in macromolecules that normally contain phosphate, most notably nucleic acids and proteins. (from Wolfe-Simon et al.; reference below; click through at the bottom)
In an accompanying news article, Elizabeth Pennisi quotes two scientists commenting on the report:
"This is a very impressive and exciting discovery," says Barry Rosen, a biochemist at Florida International University in Miami. "The implication of this work is that life can be quite different from what we know," agrees [Clara] Chan, [a geomicrobiologist at the University of Delaware.To understand which the discovery would be so impressive, if it turns out to be right, just remember that the backbone of DNA is composed of bonds between phosphorous atoms. The claim that Wolfe-Simon and her collaborators make is that phosphorous can be replaced with arsenic in DNA. In fact, if that claim turns out to be right, it won't be merely "impressive" or "exciting". It will be truly astounding.
So why did I qualify what I wrote? Why did I write "if it turns out to be right" instead of simply writing "to understand why the discovery is so impressive..."? Click through for more of the story.
In fact, my first reaction when I heard about the story was, "Wow! That is truly astonishing." I looked up the paper in Science, read the abstract, and repeated myself. It completely blew my mind. Not being a microbiologist or a biochemist, though, I didn't think much more about it. Since the paper had survived peer review at Science, I figured the results, though completely contrary to anything I could have imagined were sound -- until I ran across some withering critiques of the paper.
Rosie Redfield1 posted a detailed critique on her blog on the Saturday after Wolfe-Simon appeared.2 You should read the whole thing if you're interested in the topic, but here's the bottom line:
But that's not the end of the story. However this turns out, whether it turns out that Wolfe-Simon and her colleagues have found a bacterium that can substitute arsenic for phosphate in biological macromolecules or that the critics are right, this is how science works. One scientist (or a set of scientists) make a claim. They submit that claim to peer review. If the claim is particularly unexpected or exciting, reviewers and editors are likely to be pretty skeptical, but if the reviewers and editors think the evidence presented is strong the reviewers will recommend that the paper be published, and the editors will accept their advice.
And that's not the end of the story either.
Once the paper appears, scientists around the world read it. Sometimes scientists who weren't part of the review process see what they regard as flaws or deficiencies in the paper. If those flaws are egregious enough, they'll write a response to the paper outlining their critique and send it to the editor. Depending on the journal and the type of critique they offer, the editor may decide whether to publish the critique without seeking input from reviewers or (s)he may ask for advice from reviewers on the critique. Either way, there's no guarantee that a critique will be accepted just because it's been submitted. In this case, Rosie submitted a letter to Science. I don't know whether the editors have decided yet whether to publish it.
And even that's not the end of the story. Here's how Carl Zimmer ends his story in Slate:
Compare that lengthy, tortuous process of debate and review among experts to the "debate" that intelligent design creationists want to have in high school textbooks. Which process do you think is most likely to help kids understand their world?
1In the interest of full disclosure, I should mention that Rosie and I overlapped in graduate school at Stanford. I've run into her once or twice at professional meeting since then, but that's been our only contact since then.
2Rosie's blog isn't a typical science blog. She uses it to record her day to day thoughts about research in her lab. As she says at the top of the post as it appears now: "I wrote this post on Saturday Dec. 4, mainly to clarify my own thinking. I didn't expect anyone other than a few researchers to ever read it."
Wolfe-Simon, F., Blum, J., Kulp, T., Gordon, G., Hoeft, S., Pett-Ridge, J., Stolz, J., Webb, S., Weber, P., Davies, P., Anbar, A., & Oremland, R. (2010). A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus Science DOI: 10.1126/science.1197258
Rosie Redfield1 posted a detailed critique on her blog on the Saturday after Wolfe-Simon appeared.2 You should read the whole thing if you're interested in the topic, but here's the bottom line:
Basically, [the paper] doesn't present ANY convincing evidence that arsenic has been incorporated into DNA (or any other biological molecule).Carl Zimmer, the science writer, was smart enough to be a little skeptical when the paper appeared. He saw Rosie's critique and contacted a number of other scientists to ask for their assessment of the paper. He wrote in Slate that "[a]lmost unanimously, they think the NASA scientists have failed to make their case."
But that's not the end of the story. However this turns out, whether it turns out that Wolfe-Simon and her colleagues have found a bacterium that can substitute arsenic for phosphate in biological macromolecules or that the critics are right, this is how science works. One scientist (or a set of scientists) make a claim. They submit that claim to peer review. If the claim is particularly unexpected or exciting, reviewers and editors are likely to be pretty skeptical, but if the reviewers and editors think the evidence presented is strong the reviewers will recommend that the paper be published, and the editors will accept their advice.
And that's not the end of the story either.
Once the paper appears, scientists around the world read it. Sometimes scientists who weren't part of the review process see what they regard as flaws or deficiencies in the paper. If those flaws are egregious enough, they'll write a response to the paper outlining their critique and send it to the editor. Depending on the journal and the type of critique they offer, the editor may decide whether to publish the critique without seeking input from reviewers or (s)he may ask for advice from reviewers on the critique. Either way, there's no guarantee that a critique will be accepted just because it's been submitted. In this case, Rosie submitted a letter to Science. I don't know whether the editors have decided yet whether to publish it.
And even that's not the end of the story. Here's how Carl Zimmer ends his story in Slate:
Critics say that a few straightforward tests on the bacteria would show whether they really do have arsenic-based DNA once and for all. And the NASA scientists say they're ready to hand out GFAJ-1 to researchers who want to study it. This controversy may be burning brightly at the moment, but it probably won't burn for long.Exactly. Wolfe-Simon and her colleagues will give other scientists samples of the bacterium that is claimed to have these extraordinary properties and those scientists will have a chance to verify Wolfe-Simon's claims. If Wolfe-Simon's claims turn out to be right, textbooks will be rewritten, and all of us will have to think differently about the chemistry of life. If her claims turn out to be wrong, only a few specialists will remember that the paper was ever published.
Compare that lengthy, tortuous process of debate and review among experts to the "debate" that intelligent design creationists want to have in high school textbooks. Which process do you think is most likely to help kids understand their world?
1In the interest of full disclosure, I should mention that Rosie and I overlapped in graduate school at Stanford. I've run into her once or twice at professional meeting since then, but that's been our only contact since then.
2Rosie's blog isn't a typical science blog. She uses it to record her day to day thoughts about research in her lab. As she says at the top of the post as it appears now: "I wrote this post on Saturday Dec. 4, mainly to clarify my own thinking. I didn't expect anyone other than a few researchers to ever read it."
Wolfe-Simon, F., Blum, J., Kulp, T., Gordon, G., Hoeft, S., Pett-Ridge, J., Stolz, J., Webb, S., Weber, P., Davies, P., Anbar, A., & Oremland, R. (2010). A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus Science DOI: 10.1126/science.1197258
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