I have an idea. (No, it was not beginner’s luck.) The idea came to me while listening to University of Chicago evolutionary geneticist Jerry A. Coyne give a talk on a cruise ship in early March. If you remember last month’s column, you already know about the hardships of science lectures on the high seas, where “buffeted” refers not to the effects of winds and waves but to the feeling you get after one too many trips to the smorgasbord. But I digest. I mean, digress.
Creationists argue that speciation has never been seen. Here’s part of a December 31, 2008, posting by Jonathan Wells on the Web site of the antithetically named Discovery Institute: “Darwinism depends on the splitting of one species into two, which then diverge and split and diverge and split, over and over again, to produce the branching-tree pattern required by Darwin’s theory. And this sort of speciation has never been observed.”
The claim makes me think of the trial where a man was charged with biting off another man’s ear in a bar fight. (Incredibly, Mike Tyson was not involved.) An eyewitness to the fracas took the stand. The defense attorney asked, “Did you actually see with your own eyes my client bite off the ear in question?” The witness said, “No.” The attorney pounced: “So how can you be so sure that the defendant actually bit off the ear?” To which the witness replied, “I saw him spit it out.” We have the fossils, the intermediate forms, the comparative anatomy, the genomic homologies—we’ve seen what evolution spits out.
Back to the ship. Coyne’s address was on the vast amounts of incontrovertible scientific evidence available for evolution. (To recapitulate the cruise experience, you can simply read Coyne’s new book, Why Evolution Is True, while overeating.) As Darwin did before him, Coyne noted that the development of new breeds through artificial selection is a good model for the evolution of new species by natural selection. He then offered a comment about dog breeds, also found in his book: “If somehow the recognized breeds existed only as fossils, paleontologists would consider them not one species but many—certainly more than the thirty-six species of wild dogs that live in nature today.”
Even incredibly closely related populations of organisms are typically considered different species if there is some kind of reproductive barrier between them. And it doesn’t have to be mismatched chromosomes. Could be a mountain if you’re not a goat. Could be a molehill if you’re not a mole.
Duke University’s Mohamed Noor, who was also lecturing onboard the ship, studies such barriers. His accomplishments include winning the Linnean Society’s Darwin-Wallace Medal, given out every 50 years for evolutionary research. If Jonathan Wells studied the right 49-year period, he might argue that it’s impossible for anyone to win the award because that kind of recognition has never been observed.
Noor looked at the fruit flies Drosophila pseudoobscura and D. persimilis. In the lab, he can get a female D. pseudoobscura to mate and produce some fertile offspring with a male D. persimilis. Out in the world, however, it doesn’t happen—she hates his smell, his song, his mating dance.
So here’s the idea you’ve been patiently waiting for: let’s simply say that dog breeds are different species. Take two that Coyne highlights for their differences—the 180-pound English Mastiff and the two-pound Chihuahua. They’re both considered members of Canis lupus familiaris, and in principle artificial insemination could produce some sort of mix or possibly an exploding Chihuahua. But face it, the only shot a male Chihuahua has with a female Mastiff involves rock climbing or spelunking equipment.