You may remember that in September, retired Liverpool professor Donald Williamson published a paper in The Proceedings of the National Academy of Sciences claiming that the caterpillar stage of the butterfly/moth life cycle arose when an ancient lepidopteran mistakenly mated with a velvet wom (onychophoran), producing an inter-taxon hybrid that had an adult butterfly but the larval form of the worm. The whole idea seemed ludicrous for many reasons (I called it “the worst paper of the year“), but of course ultimately Williamson’s view needed a formal appraisal in the scientific literature.
Now, in a new paper in PNAS, Michael W. Hart and Richard K. Grosberg give this appraisal and conclude that, on the basis of data that already exist, Williamson’s idea is full of it. Among their criticisms are these:
1. Contrary to Williamson’s prediction, the genomes of Lepidoptera are generally smaller than those of other orders of insects that lack the larval stage, and are certainly not the large size you’d expect if modern butterflies resulted from hybridization between a purely flying ancestor and a wormy onycophoran.
2. Similarly, contrary to Williamson’s predictions, the genomes of onycophorans are not smaller than those of Lepidoptera or of other “holometabolous” insects that undergo a striking transformation between larval and adult stages.
3. Contrary to Williamson’s prediction, DNA sequencing shows NO close relationship between any lepidopteran genes and any genes in onycophorans.
There is other evidence as well, but the above is sufficient to completely refute Williamson’s claims. I stand by my characterization of his paper as the worst of the year.
You can see Scientific American’s report on the Hart and Grosberg paper here.
Well, that takes care of that. The remaining issue is how did this execrable piece of work get published in the first place? The communicating editor was Lynn Margulis, who is a huge booster of evolutionary processes that involve hybridization, undoubtedly because of her pathbreaking work showing that mitochondria and chloroplasts of eukaryotic cells used to be bacteria. She even wrote a book suggesting that hybridization may be the key to understanding the origin of species. (She’s wrong except for allopolyploidy in plants.) Handling this paper, Margulis appeared to violate journal policy by asking reviewer after reviewer to look at it until she got the positive reviews needed to assure publication. But, as Scientific American reports:
In August, when Williamson’s paper was published, Margulis told Scientific American that she needed “6 or 7” peer reviews to secure the “2 or 3” positive responses needed to present the work for publication. That statement set off a cascade of criticism of PNAS‘s two-tiered submission process and, according to Nature News, led the journal’s editor in chief to write to Margulis demanding “a satisfactory explanation for [her] apparent selective communication of reviews.” Her reply, obtained by Nature News, explained that three researchers had declined for scheduling reasons or lack of expertise, and two were omitted from the official PNAS submission because they lacked formal credentials.
Um. . . “lacked formal credentials”?? Why, then, were these reviewers asked in the first place? Shame on PNAS for publishing Williamson’s paper; it was a complete waste of journal space and required several scientists who are busy with other things to sit down and refute it.
Doesn’t the journal have scientifically-literate people (beyond the editor of each paper) who monitor their submissions for quality?
Fig. 1. Peripatus, an onycophoran but not a direct ancestor of the caterpillar.
Hart, M. W. and R. K. Grosberg. 2009. Caterpillars did not evolve from onychophorans by hybridogenesis. Proc. Nat. Acad. Sci. USA. online. (You can get the PDF file from this link.)