Convergence: Explanation or Rescue Device?
The news media are telling us that bats and dolphins both hit on the same genetic pathway to evolve echolocation – even though they are on vastly different evolutionary lineages and use echolocation differently (one in air, one in water). Since it is inconceivable that a putative shrew-like common ancestor of these very different animals already had echolocation, the biologists claim that dolphins and bats followed the same evolutionary pathway, even down to the evolution of a single molecule. Is this an explanation of how they came to have these traits, or a rescuing device intended to save evolutionary theory from the evidence?
Science Daily and New Scientist both echoed the conclusions of two papers in Current Biology.1,2 The papers found that phylogenetic trees based on the cochlear gene Prestin include bottlenose dolphins and microbats together. They claim to have ruled out all other hypotheses (such as horizontal gene transfer, DNA contamination, gene paralogy, long-branch attraction, and biased amino acid frequencies) as unlikely, so “convergence” must explain the similarities. In short, natural selection converged on the same genetic set of mutations to the Prestin gene because echolocation was adaptive.3 The first paper concluded, “Regardless, our findings of adaptive sequence convergence between two highly divergent groups that share a complex phenotype is unprecedented, and suggests sequence convergence may be more common than previously suspected.”
But what does convergence mean? Is it a law of nature? Does it convey understanding, or is it a term acting as a placeholder for ignorance? The explanation begs numerous questions. How do they know the extent to which this one protein proves essential for echolocation over other parts of the echolocating organs that are not convergent? If echolocation is such a strong adaptive trait, why did it not evolve in all whales and bats, as well as in beavers, sea lions, and all nocturnal mammals, which could presumably make good use of it? If the answer to that question is contingency, then how does convergence differ from the null hypothesis – i.e., the non-explanation, “stuff happens”?
A review of the two papers in the same issue of Current Biology4 revealed that the convergence explanation is not so straightforward. Gareth Jones (U of Bristol) reminded readers that molecular phylogenies often conflict with morphological phylogenies or with each other. “A key question is whether convergent, adaptive evolution dominates phylogenetic signals, or whether neutral evolution overrides any convergence driven by natural selection when making phylogenetic inferences,” he said. “In reptile mitochondrial genes, although molecular convergence is clearly apparent, the specific selective forces driving such convergence are not obvious.” He noted that the prestin modifications might be due to adaptive needs to hear high frequencies, but noted that other animals, like some mice, communicate with high frequencies but do not have the convergent-prestin signature. He also noted that the new phylogenetic tree of bats based on prestin conflicts with other phylogenetic trees based on large-scale genetic analyses of both nuclear and mitochondrial DNA: “hence,” he said, “phylogenetic signals based on functional gene sequences may be misleading when reconstructing the evolutionary history of bats.”
The prestin study actually creates additional problems. Jones said it “emphasises the necessity of avoiding the use of putative functional genes in estimating evolutionary history.” Researchers will have to incorporate more data sets, and consider the effects of neutral drift, when building phylogenetic trees. Finding the signature of natural selection, therefore, will require human selection: “careful selection of genetic data that are probably neutral (intron sequences, for example).” But how will the researcher select the data sets that produce the inference he wants without circular reasoning? A data set that produces a signature of natural selection might be selected over other data sets that do not. It would not, therefore, be the signature of nature itself. Even so, examples of molecular convergence may be uncommon, Jones said. That means their usefulness for inferring natural selection may be limited, despite the cheerleading of the popular press.
1. Liu, Cotton, Shen, Han, Rossiter and Zhang, “Convergent sequence evolution between echolocating bats and dolphins,” Current Biology, Volume 20, Issue 2, 26 January 2010, Pages R53-R54, doi:10.1016/j.cub.2009.11.058.
2. Li, Liu, Shi, and Zhang, “The hearing gene Prestin unites echolocating bats and whales,” Current Biology, Volume 20, Issue 2, 26 January 2010, Pages R55-R56, doi:10.1016/j.cub.2009.11.042.
3. For information about prestin, a remarkable motor enzyme in the inner ear, see the 07/31/2007 entry and its embedded links.
4. Gareth Jones, “Molecular Evolution: Gene Convergence in Echolocating Mammals,” Current Biology, Volume 20, Issue 2, 26 January 2010, Pages R62-R64, doi:10.1016/j.cub.2009.11.059.
In the land of Jargonwocky, a scientist named Niwrad came up with a theory of everything he called Galumph. With frabjous joy, he investigated all the creatures of the borogoves with his apprentice, Ecallaw. He found that the Jubjub birds had round eyes and the mome raths, though similar, have square eyes. That’s because of Galumph, he explained. The Bandersnatch and Jabberwock, though looking very different, both have round eyes. “Galumph triumphs again!” Niwrad chortled. “But how can that be?” burbled Ecallaw with uffish look. “They are so very different in other respects.” “Callooh! Callay!” exclaimed Niwrad frumiously. “’Tis only to demonstrate the power of Galumph. The former is a case of Parallel Galumph. This one, a case of Convergent Galumph. Do you see? Galumph explains all. We must away and tell Yelxuh, our mimsy publicist, to announce our scientific triumph to the townspeople! We have slain the mystery of Jabberwock with Galumph. Galumph has wiped the brillig from our slithy toves, and given us Enlightenment!”
Convergence is about as meaningful and convincing an explanation as this. If God exists, and if it were his intent to show the impossibility of evolution, he could hardly have done a better job than to show both unity and diversity of plants and animals, but with cross-branches linking unrelated lineages with similar traits. It would simultaneously show a single Creator (instead of polytheism) and the impossibility these complex species and traits had emerged naturally from common ancestry. As far as the differences between bat species, it is also much more plausible to explain by trait loss rather than by innovative gain of new complex systems. Yet the Darwinists, intent on their naturalistic world view, have come up with a term like Galumph, called Convergence, to rescue their beliefs from the evidence. To see the extent of their use of this rescuing device, look at Brett Miller’s partial list of incredible similarities between unrelated creatures in his essay, The Convergence Concoction. Like his final cartoon shows, it’s so much easier for lazy scientists to say “It evolved!” than to consider the implications of the evidence. Another resource on the explanatory flimflam being sold as Convergent Evolution can be found in this article on the Explore Evolution website, section II D.
It can look impressive to see in scientific papers the amount of detailed work researchers perform to arrive at their Galumph explanations. How could all these analytical tools like Bayesian analysis, software that generates phylogenetic trees out of genetic inputs, mathematical manipulations, inscrutable jargon, tables, charts and piles of supplemental data be misguided? How can it be wrong when it feels so right? But if the conclusion of this bridge over troubled water is “Galumph! Stuff happens,” it doesn’t matter. That’s a non-starter as an explanation. And busy work is not science. Undoubtedly one could find similar amounts of complex procedures and data manipulation in the textbooks on alchemy and astrology. Couching the Stuff Happens Law (09/15/2008 commentary) in euphemisms does not produce understanding.
By failing to include the top-down theories in their roster, they have failed to address the pool of possible explanations. Regardless, this jabber about Convergence is not an explanation; it’s Jargonwocky masquerading as meaning.