Apparently, Michael Behe just doesn’t know when to pack it in. In reply to Travis’s essay in Science, “On the Origin of The Immune System” (see previous PT posts: 1, 2), Behe has posted a letter he sent to Science. Instead of just sucking it up and admitting that his statements in Darwin’s Black Box that
“As scientists we yearn to understand how this magnificent mechanism came to be, but the complexity of the system dooms all Darwinian explanations to frustration.” (Darwin’s Black Box, p. 139)
We can look high or we can look low, in books or in journals, but the result is the same. The scientific literature has no answers to the question of the origin of the immune system. (Darwin’s Black Box, p. 138)
…were wrong, or at the very least became wrong in the time between 1996 and 2005, Behe is still expressing proud, Kierkagaardian-esque defiance. In this (rejected) letter to the editor of Science, Behe reiterates his proud stand that the work of an entire field, the life’s achievements of hundreds of immunologists, complete with surprising experimental support for a surprising hypothesis (the transposon hypothesis), still has “no answers” to the question of how it evolved, and that Darwinian explanations are “doom[ed].”
Well, actually, he doesn’t quite say that, because somewhere along the line Behe retreated from his bold rhetoric, without ever admitting that he made an error (this is, I think, the key to understanding Behe: he will never, ever, admit a significant error). What Behe does now, as in his letter, is nitpick on subsidiary points, and conclude that because scientists don’t agree on everything, he is still justified in ignoring everything they have all come to agree on.
In the courtroom scenario Travis recounts, I was testifying that science has not shown that a Darwinian mechanism could account for the immune system. Travis’s article itself confirms that is still true. He cites some biologists who think the adaptive immune system arose in a “big bang”; he quotes other scientists who assert, “There was never a big bang of immunology.”
But just how significant is this debate in the grand scheme of things? The “big bang” idea essentially was based on the idea that the transposon insertion event kicked off a rapid diversification of the machinery of adaptive immunity. If you restrict your view of adaptive immunity to RAG (Recombination-Activating Genes) and VDJ recombination, it does appear that they appeared “suddenly” in jawed vertebrates (with “suddenly” meaning 50 million years). The “simple” transposon hypothesis provided an explanation – a rare mutational event in just the right place made things possible that were not possible before.
The questioning of the big bang model (which IDists/creationists would love to keep, actually, because they love anything “sudden” sounding, except that in this case they’d have to accept the transposon hypothesis) came when additional data showed that various “parts” of adaptive immunity, more broadly considered, are indeed distributed amongst the relatives of jawed vertebrates. Also, homologs of the RAG genes have been found in other deuterostomes, which makes it plausible that the transposon ancestral to RAG was already bouncing around in genomes before it took a key role in adaptive immunity. We won’t know which hypothesis is more likely correct until we get a bunch more genomes and biochemistry on the RAG homologs in them (I’m betting on the second hypothesis, based on my principle that Claimed Big Bangs in Biology Always Go Poof When You Look at Them Up Close; but we’ll see).
But in the grand scheme of things, this sort of thing is small potatoes. Both sides of this “argument” (I doubt anyone is very emotional about it) acknowledge that key remarkable features of the VDJ recombination system are ultimately derived from a transposon, and that the this very surprising, very evolutionary hypothesis received dramatic confirmation in recent decades. Both sides would agree that this is One Of The Friggin’ Answers about the origin of adaptive immunity that a guy like Behe should accept if he was actually fairly assessing the science and not just blindly trying to avoid admitting error.
To sum up, the “big bang” question is a subtle thing that depends on all kinds of subtle points – what does/should one mean by “big bang”, how are we going to delineate the borders of “adaptive immunity” such that it may or may not have banged, what does “sudden” mean anyway when “sudden” can mean 50 million years, etc. To pretend that splitting hairs over these points constitutes a serious challenge to widely-accepted discoveries in the field is silly.
[Travis] discusses vertebrate immunologists who think they know what the selective advantage of the system is; he quotes invertebrate immunologists who feel otherwise. So are we to think that its history is uncertain and even its selective advantage is unknown, yet the mechanism by which the adaptive immune system arose is settled?
Let’s back up. Does Behe seriously think that it is possible there is no selective advantage for adaptive immunity? That’s not what he said at trial (1, 2). Neither he nor anyone thinks that. So actually, he’s just dissembling here . The debate Travis mentions is, again, subtle. Organisms without adaptive immunity still have all other sorts of immune system defenses, and they seem to get by, so in that context what was the specific sub-category of extra advantage that adaptive immunity gave? This is a subtle and complex question. The basic answer is probably that diversity in immune receptors is good (there is massive evidence for this in almost every immune system, adaptive or not), and RAGs allowed for increased diversity, and that’s basically it. It may be that adaptive immune systems are more economical (the organism can get by with fewer immune cells in total; although, it is still the case that something like 1% of our cells are immune cells), or make it easier to be longer-lived and slower-reproducing (like many vertebrates, compared to invertebrates), or be social animals with lower costs in terms of the spread of disease, or (as Travis mentions) improve the ability to distinguish friendly from unfriendly bacteria (although, if Crohn’s disease is any guide, it appears that our sophisticated immune system has way too much of a propensity to misfire and attack helpful bugs and even our own cells). But again, these are all subtle sub-hypotheses of the basic idea that receptor diversity and memory are useful for fighting off invaders, which is something not in dispute – not even by Behe, if he were being forthright and paying attention to his own testimony and what he said in Darwin’s Black Box.
One can take any broad scientific question, ignore the basic conclusions a field has reached, and push out to the more detailed points where active debate occurs – indeed, this is made easy by the fact that scientists work and publish most actively at exactly those points, that’s what doing science is about. But citing such debates in a cheap attempt to discredit the basic points those experts agree on is an exceedingly weak argument. Behe is free to do it, but it is completely legitimate to keep bringing up embarrassing topics like evolutionary immunology as long as he does.
1. Behe also sometimes argues that the evolutionary immunology literature only relies on common ancestry, and doesn’t cover mutation or selection. But as I showed, Behe himself admitted selective advangtage for the immune system here and here, and furthermore he admitted transpositions are mutations here and here. So he’s sunk even on the narrow point, unless he retracts some of his testimony.