Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
UPDATE: I’m informed that the Conference is now sold out. For those of you who got tickets, enjoy!
Atheist Ireland has asked me to note that there are only 20 tickets left to the World Atheist Conference, held in Dublin from June 3-5. (Tickets are €100 and can be bought at this link.) The program (here) is quite diverse, featuring not only the usual suspects, but some new voices as well, and a panel discussion on women activist atheists.
Well, the gene was actually located but not yet identified. Nevertheless, it soon will be.
This story is about what many evolutionists consider our best-documented example of natural selection in real time: the evolution of “industrial melanism” (dark color in response to environmental pollution) in the peppered moth, Biston betularia. The normal appearance of the moth is whitish with black specks (accounting for its name; it’s also called the “typica” form):
Photo by Bob Fredrick from Arkive
In the early nineteenth century, a few all-black variants of this form (called “carbonaria”) had been found by British collectors (the first was described in 1848), but they were in very low frequency: only a few hundredths of one percent. (The Brits are diligent amateur lepidopterists, and so the records are pretty good). Later genetic tests showed that the difference between carbonaria and typica was due to a single gene, with the dark color being dominant.
By 1898, the frequency of the dark form had skyrocketed, reaching 98% in the woods around Manchester. It rose as well in other parts of England, particularly the industrialized parts. In rural areas the frequency of the dark variant was lower. This concerted rise in such a short time surely indicated the operation of natural selection. Although there were several theories about how this operated, the most likely seemed to be based on camouflage: as industrialization darkened the tree trunks with soot, and killed the lichens, the typica form was no longer cryptic on the formerly light-colored trees (especially birches), and now the dark form was camouflaged instead. Here are some photos showing how the dark form is conspicuous on darkened trunks and the light form on normal, non-sooty trees:
Note that there are two moths in each picture.
When Britain passed Clean Air Acts in the 1950s, the pollution began to abate and the trees lost their darkness: the soot washed off, and lichens began to return. Sure enough, the color change reversed itself: the light-colored moths began to increase in frequency, so that now the typica form is present in frequencies of 90% in areas, like Manchester, where it had almost vanished. Here are what the two color morphs look like in a contemporary unpolluted woodland:
As I said, the concerted rise and fall of color genes throughout Britain indicated the action of natural selection, a hypothesis supported by similar changes in the American subspecies of B. betularia, particularly in polluted areas in Michigan and Pennsylvania.
The hypothesis that the selection on color was based on predation—especially by visual predators like birds, who love to eat moths—was tested by British biologists, particularly Bernard Kettlewell at Oxford. He released mixtures of dark and light moths in both polluted and unpolluted woods. As expected, in each type of wood he recaptured more of the moths that matched the trees, suggesting that the conspicuous moths had been eaten more often. His estimate of selection against conspicuous moths was quite strong: they appeared to have had only half the reproductive output of the camouflaged moths.
I had been a severe critic of Kettlewell’s experiments, which were cited in all the textbooks as proving natural selection in real time. His experimental design had several fatal flaws. But more recent work has shown that dead moths of different colors pinned to trees of different colors do show the expected differences in attack by birds, and that in nature moths indeed rest on tree trunks and limbs. Even more recently, Michael Majerus of Cambridge University repeated Kettlewell’s release experiments, but did them correctly. Sure enough, he found the expected differential recapture of light and dark forms. Sadly, Majerus died of mesothelioma before his data could be published, and so the results of the strongest test of selection in this system still reside, as far as I know, on websites rather than the pages of reviewed scientific journals.
At any rate, the Biston betularia story stands, next to the Grants’ work on medium ground finches in the Galápagos, as one of the best-understood instances of selection occurring in “real time.” (“Industrial melanism” is not limited to Biston betularia, by the way: around 70 species of Lepidoptera also showed similar changes.) Only one piece of the story was missing: the genetic basis of differences between light and dark forms. It was, as I have said, known to result from a single gene, with the dark “allele” being dominant, but the nature of that gene wasn’t known.
This week, however, a paper in Science by Arjen van’t Hoff et al. took a large step to identifying the “melanism” gene. The authors mapped this single genetic factor to a small chromosome region by crossing light and dark moths that differed by many genetic markers, and noticing which genetic markers were associated with wing color in subsequent generations. The “color gene” resided on a small section of chromosome homologous to chromosome 17 in Bombyx mori, the silkworm moth, whose genome has been mapped. The authors haven’t yet narrowed down this small region to one specific gene, for that is very hard to do, and there are no obvious “candidate genes” in that region that affect color.
What is most interesting, however, is that the genetic analysis of various color forms collected throughout the UK gave information about the evolutionary origin of the black form. It could have originated in two ways: either a single unique dark mutation, in a single carbonaria moth, could have spread throughout Britain, or there could have been multiple origins of the mutation (each, perhaps, kept at low frequency by natural selection against the dark color), all of which began to rise in concert when the environment changed.
Genetic studies showed that the first hypothesis was the most likely. All the carbonaria individuals carried a unique genetic signature around (not in) the “dark” gene, suggesting that that signature was the unique DNA of a single mutant individual that, because the DNA was physically close to the dark gene undergoing selection, “hitchhiked” to high frequency along with the dark allele itself. (Remember that nearby genes reside on a single stretch of DNA, so if one part of that DNA rises in frequency due to selection, it carries with it nearby regions as well. More distant regions, however, lose this association because of genetic recombination between DNA strands.) If the dark coloration in British moths had stemmed from several or many different dark mutations at an initially low frequency, you wouldn’t expect the “dark” region to have a unique genetic signature shared by all currently dark individuals.
So this settles one aspect of the melanism story. The rest of the story will follow soon: the identification of the precise gene distinguishing light and dark forms, and the sequencing of that gene to determine if the color difference is due to a “structural” difference residing in a protein, or to a “regulatory” difference affecting whether or how a protein is expressed. But this molecular-genetic work is just icing on the cake, for regardless of the precise genetic basis of the color difference, the broad outlines of the story—and the validity of B. betularia as a case of natural selection in “real time”—are clear.
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A.E. van’t Hof, N. Edmonds, M. Dalíková, F. Marec, and I. J Saccheri. 2011. Industrial melanism in British peppered moths has a singular and recent mutational origin,” Science 332:958-960.
Here’s our first cat backpacker, or rather backpacked cat.
In 2008, a French couple, Guillaume and Laetitia, left Miami for a hike. Their goal: Tierra del Fuego, on the tip of South America and 15,000 km from Miami. Their restrictions: they had to do it all on foot, and their budget was limited to one Euro per day each! Two months in, in Lousiana, they found a small gray kitten, which they promptly named Kitty. Kitty has become part of the trek, and is toted along in a backpack:
The pair (Laetitia bailed out in September) is now in Colombia, and you can follow the adventures of Guillaume and Kitty on the expedition website (note: you’ll have to be able to read French, but if you can’t there are many videos and photos). There is some dissent about this trek, centering on the advisability of toting a cat along instead of giving it a good home. And, if they’re only in Colombia after three years (the projected length of the entire hike), the enterprise may have hit a snag.
There are many more videos here, with lots showing Kitty.
And, of course, the journey has a Facebook site.
At the beginning of May, four peregrine falcon chicks (Falco peregrinus) hatched at the Evanston Public Library, just north of here. There’s a 24-hour FalconCam that you can watch here, and there’s also a website detailing their activities. The parents, Nona and Squawker, seem to be the same ones who have nested there in previous years.
The chicks will be banded next Tuesday at 11 a.m. Chicago time; this will apparently be broadcast live.
Here’s a recent video of one of the parents feeding them.
by Matthew Cobb
Jerry’s back in town so I really shouldn’t be posting here without his OK, but I couldn’t resist this LOLant that Myrmecos has just posted and tweeted… My guess is Jerry might twitch his lip, too… I note that LOLants (or this one anyway) can spell better than wot our kittehs kan.
Yes, I know a fair number of my readers think that courses on vampires, Batman, and the like are perfectly valid things to have at a good university, and I’m not averse to academic studies of popular culture. But there are limits.
This is one of them. A student at the University of Chicago has organized a one-day academic conference on (Ceiling Cat help us) the television show “Jersey Shore.” I have watched bits of it in hotel rooms, and it’s about as dire a show as it comes: an MTV “reality documentary” about a pack of drunken, sex-obsessed youngsters who booze, brawl, and bonk their way through various cities. The student, who must have gotten university funding for this venture, explains:
“I think it’s very important for academics not to restrict their work to so-called “high culture,” but to seriously engage with popular culture as well,” Showalter said via email. “The images and sounds of pop culture surround us and entertain us, and for those reasons alone they are deserving of study. With regards to ‘Jersey Shore’ specifically, I believe the show is both a fascinating and innovative example of reality television, as well as a useful lens through which to examine many of the issues that animate contemporary life: problems around gender roles, ethnic identity, celebrity, the influence of mass media, the notion of ‘reality’ itself, and so on.”
The response on campus has been positive overall, according to Showalter, who said the conference part of the “uncommon” tradition U of C prides itself on. So far, the conference will include talks from University of Michigan Professor Candace Moore, University of Western Ontario Professor Alison Hearn and Gawker’s Brian Moylan. . .
. . . “I hope the conference attendees gain a new appreciation for Jersey Shore as a cultural document, realize that even shows that are derided as vulgar or lowbrow have important things to tell us, and learn to be more thoughtful consumers of pop culture themselves. I hope the conference inspires other students to fully pursue their academic interests, no matter how unusual they may seem to others.”
Oh, and for the record, Snooki is Showalter’s favorite cast member, though he said Pauly D. always has the best lines.
Where have we failed? Is this a good way to spend university money (or students’ time) on broadening our academic horizons? I don’t think so.
On the other hand, since I’m already here maybe I can give a paper, too. How about this: “Gym, Tan, and Laplace: How The Situation uses science to attract women.”
The gang. Right to left: Pauly D, Snooki, and The Situation (kneeling).
Every lab worth its salt has its own tee shirt, and I’m wearing mine for the first time. Sporting an endemic fly, it was designed by the mother of one of my undergraduates. The boots and booze are obvious; I haven’t mentioned my penchant for Hawaiian shirts and Cuban cigars.
I’m so glad that Eric’s website, Choice in Dying, has taken off in a big way. He regularly posts thoughtful commentaries, and, unlike most of us, can’t be accused of theological naivité (he was, after all, an Anglican priest). And although his website was originally designed to defend assisted suicide, he’s gone far beyond that, into the ambit of religion in general. (It’s hard for some of us to adhere to our stated missions: I originally intended to limit my posts to new evidence for evolution, and to write only rarely.)
Eric has now started doing what somebody had to do: defending Dawkins’s The God Delusion, which he sees as the most influential of Gnu Atheist books. At the evolution meetings in Banff last week, I heard the book dissed twice by biologists—and for no good reason. When you press fellow atheists for the reason they don’t like it, they either say that they learned nothing from it (of course, they were atheists when they opened the book!), or they hem and haw and mutter something about Dawkins’s failure to engage “sophisticated” theology—a really dumb criticism given the book’s mission and audience.
Eric is defending the book in a series of posts, critic by critic, and will show, I suspect, that their criticisms don’t hold water. He certainly does this in his first post of the series, in which he dissects Alvin Plantinga’s attack on The God Delusion in his book The Dawkins Confusion. (Many attacks on Richard’s book have dire and unfunny titles, demonstrating once again that accommodationists have no sense of humor). It’s a long piece, and I won’t summarize it here except to say that it’s good and you should read it. I particularly like Eric having to instruct Plantinga on how science really works, and why it’s foolish to maintain, as Plantinga does, that god is “maximally probable.” (How does Plantinga, whom Eric describes as perhaps “the foremost Christian philosopher writing in English,” manage to get famous writing such tripe?)
I do want to take issue, though, with two minor points of Eric’s analysis.
1. You can’t prove a negative. This is one of the most common defenses of God, and it’s simply wrong—or at least incomplete. “You can’t prove that God—or anything—doesn‘t exist,” they say. Eric agrees:
And, in any event, as Plantinga already knows, an argument purporting to demonstrate the non-existence of something is bound to fail.
But that’s wrong. If there should be empirical evidence for the existence of something, and thorough investigation finds no such evidence, one can reasonably conclude that it doesn’t exist. We can prove that Santa Claus doesn’t exist, and we can prove that the Loch Ness Monster doesn’t exist. Both apparitions should leave detectable evidence, but there is none. (I use “proof” here to mean “evidence of nonexistence so strong that any reasonable person would accept it”. Science, of course, doesn’t really “prove” anything—even positives—in the sense of proof as “existence beyond doubt.”) If you claim that Jerry Coyne doesn’t have a Ferrari, you can prove that, too, for there are no records of Ferraris being sold to me, no evidence that I’ve ever withdrawn money to pay for one, and no observations that I’ve ever driven one.
And, like the Loch Ness Monster, a theistic god should have left traces of its existence. But we don’t have any. Prayer doesn’t work, there’s no evidence for true miracles or an afterlife, and the world doesn’t look like it was organized by a loving and omnipotent god. Of course we can’t prove that a deistic god, one who does nothing, doesn’t exist. But that’s true of anything that doesn’t affect the world in empirically observable ways, so assertions about those entities become uninteresting.
2. Supernatural explanations aren’t part of science. I may be misunderstanding Eric here when he talks about how the hypothesis of god is unnecessary in the scientific theory of Darwinian evolution.
No, people like the pope and Plantinga are doubtless entitled to go on thinking that, despite everything, the process is attended by a designing intelligence, but the effects are just the same whether you assume this or not, and if you do assume it you’re no longer doing science. In other words, things will remain as they are; the religious believer simply adds an irrelevant explanatory hypothesis which is not a part of science.
Well, divine intervention is irrelevant to our understanding of evolution, but one can’t say that the hypothesis of a god or designer in general is “not a part of science.” For it’s possible that there could be certain empirically detectable phenomena that would require us to provisionally invoke a deity. If prayers to Jesus worked, but not prayers to Allah, that would raise the spectre of a Christian god. I believe Eric aligns with P. Z. Myers, Anthony Grayling and others in thinking that there can be no evidence for a god, but I disagree, and I believe Dawkins does too. As always, I maintain that if the god hypothesis predicts certain phenomena that can be measured and studied, then it’s a hypothesis that can be tested. (Accommodationists, too, claim that one can’t test the supernatural, for they have a vested interest in keeping believers happy.)
Eric may be referring here only to the theory of evolution, in which case my comment is irrelevant. I suspect he’ll clarify it below.
And I hope that, in future installments, Eric deals with my ex-student Allen Orr’s review of The God Delusion, a misguided attack that appeared in The New York Review of Books. Orr, sadly, got entangled in The Courtier’s Reply:
The most disappointing feature of The God Delusion is Dawkins’s failure to engage religious thought in any serious way. This is, obviously, an odd thing to say about a book-length investigation into God. But the problem reflects Dawkins’s cavalier attitude about the quality of religious thinking. Dawkins tends to dismiss simple expressions of belief as base superstition. Having no patience with the faith of fundamentalists, he also tends to dismiss more sophisticated expressions of belief as sophistry (he cannot, for instance, tolerate the meticulous reasoning of theologians). But if simple religion is barbaric (and thus unworthy of serious thought) and sophisticated religion is logic-chopping (and thus equally unworthy of serious thought), the ineluctable conclusion is that all religion is unworthy of serious thought.
The result is The God Delusion, a book that never squarely faces its opponents. You will find no serious examination of Christian or Jewish theology in Dawkins’s book (does he know Augustine rejected biblical literalism in the early fifth century?), no attempt to follow philosophical debates about the nature of religious propositions (are they like ordinary claims about everyday matters?), no effort to appreciate the complex history of interaction between the Church and science (does he know the Church had an important part in the rise of non-Aristotelian science?), and no attempt to understand even the simplest of religious attitudes (does Dawkins really believe, as he says, that Christians should be thrilled to learn they’re terminally ill?). Instead, Dawkins has written a book that’s distinctly, even defiantly, middlebrow.