My first creationism-bashing post. Yippee.
On my “About” page, there is a link to Google’s search results for “heliconius speciation”. Several butterfly species in the genus Heliconius have been extensively studied as a possible case of hybrid speciation: individuals of two species, H. cydno and H. melpomene, are thought to have hybridized often enough that a whole new species, H. heurippa, resulted. This is pretty cool for several reasons. First, there are few good examples of hybrid species in animals; it’s much more common in plants. Second, H. heurippa does not benefit from the mimicry systems that other species of Heliconius are involved in. Third, the traditional definition of a species (for sexually reproducing organisms), the biological species concept, holds that different species are (more or less completely) reproductively isolated from each other–that is, they can’t or don’t hybridize–so hybrid species might be an exception that proves the rule. Finally, researchers have been able to re-create butterflies with wing patterns similar to those of H. heurippa from a series of H. cydno x H. melpomene crosses (and backcrosses), and these “reconstructed” butterflies seem to mate with each other more often than with members of either parent species.
Now, about those Google search results. You’ll notice among the numerous research articles this (I hesitate to actually link to it) link. This is a response from an evangelical Christian site to a study that came out a number of years ago; the study in which the H. heurippa wing pattern was originally reconstructed. The article’s title is “The Heliconius hybrid butterfly: speciation yes, evolution no”.
Now, I’ve talked to a number of creationists of various stripes. What I tend to find is that, if one sets out the argument for natural selection without getting too angry, the creationist will often agree that microevolution–changes in allele frequencies within a population–is entirely possible (well, duh, given that it’s been repeatedly demonstrated in a number of organisms in real time) and entirely within God’s plan. But they will generally say that it’s macroevolution–speciation and the generation of patterns at larger taxonomic scales than species–that they can’t believe in. And until rather recently, there were not well-proven links between micro- and macroevolution. However, there is now a strong body of evidence for the role of natural selection (i.e. a microevolutionary process) in the origin of species. Regardless, microevolution is often okay with creationists, but macro, not so much. So when I saw “speciation yes, evolution no” I got really confused.
This gem of a quote from the article explains it a bit more: “This is a fantastic example of rapid speciation—no surprise to creationists. However, it is not evolution, as no new genetic information has been produced.” The article links to another one (I refuse to give it more traffic) that explains why rapid speciation is “no surprise to creationists”; apparently it’s something to do with repopulating the earth after the Flood, though that article seems to confound rapid adaptation with rapid speciation.
So far, we have microevolution okay, speciation okay (not even surprising!), but evolution not okay. Why is that? Because “no new genetic information has been produced.” I take this to mean that no new gene or allele has appeared, and this is (probably) true. But that’s not necessarily what we mean by evolution.
Evolution as biologists understand it is the changes in patterns of (genetic) variation in populations of organisms. This includes the rise of new variation through mutation, random changes in frequencies of different variants due to demographic processes and chance events, and, perhaps most interestingly, the consequences for different variations due to their impact on an organism’s phenotype (i.e. natural selection). In the case of Heliconius heurippa, variation that was originally held in two separate gene pools (the parent species, H. cydno and H. melpomene) has been mixed in a novel way through hybridization. There may or may not be selection at play directly. But the fact that two gene pools that mingled in a limited way gave rise to a third gene pool which, at present, does not interact with the original gene pools, is an evolutionary change. The variation is now partitioned in a different way. New variation doesn’t have to be, and frequently isn’t, part of the story.
Now, to be fair, this might sound a lot like I’m the one moving the goalpost–someone points out no new information has been generated; I retreat by saying this was never necessary for evolution in the first place. But I’m not, in fact, retreating from a point; no biologist would ever have claimed that evolution meant the origin of new genetic information. This argument–the claim that there is no new genetic information–is a straw man.
And as for moving the goalposts, here’s what the creationist article says next: “The butterflies are still butterflies, with the hybrid species simply having an assortment of genes inherited from the two parent species.” And in the caption to one of the images (incidentally, not a Heliconius): “Changes in butterflies do not demonstrate bog sludge-to-butterfly evolution”. What do they expect? The change from bog sludge to butterfly has to start somewhere, and while adaptation can be rapid, it’s rarely (never?) rapid enough to generate a whole new phylum within a few generations.
This has been a rather aggravating post to write. It’s taken a week to cool off enough to get to the actual argument part and stop simply ranting. For the record, creationism-bashing posts are likely to be few and far-between on this blog.