Caterpillar Controversy Discloses Deep Evolutionary Disagreement
by Brian Thomas, M.S. *
In August 2009, retired University of Liverpool marine biologist Donald Williamson officially challenged the standard Darwinian interpretation of caterpillar origins. His paper was fast-tracked to publication by a “high-placed advocate,”1 but shortly afterward his ideas were rebutted in the very same journal. While this back-and-forth exchange has sparked intense criticism over the submission and review processes that were used, the situation also reveals core problems with broad-scale evolution.
Williamson’s paper, “Caterpillars evolved from onychophorans by hybridogenesis,” circumvented part of the standard peer-review process when it was published in the Proceedings of the National Academy of Sciences.2 The rebuttal, “Caterpillars did not evolve from onychophorans by hybridogenesis,” followed the more typical and rigorous pathway to publication.3
Williamson’s hypothesis was that insects which undergo metamorphosis evolved when an ancestral form of the “velvet worm” serendipitously cross-bred with an adult of a totally different creature. He named this process “hybridogenesis.” Williamson believes that insects “did not originate solely by accumulation of random mutations followed by natural selection.”2
Williamson offered a similar proposal in a January issue of New Scientist to explain why so many marine invertebrates that look the same in their larval stage have such radically different adult forms.4 What would cause such an experienced biologist to doubt the standard evolutionary story so strongly as to propose that new kinds formed “by the random fusion of two separate species, with one of the partners assuming the role of the larva and the other that of the adult?”5
One reason is that 150 years of searching for evidence of Darwinian gradual changes has yielded no fruit. Darwin’s idea would predict that if a species slowly morphed a fraction of an attribute at a time from one form to something entirely different, then there should be a continuum of transitional forms, each slightly different than the next.
Instead, creatures appear in either-or forms, often composed of entire mosaics of fully-formed features that are shared among different animal groups. In particular, Williamson studied the Luidia starfish, which “seems to be two species at once, one forming the larva, the other the adult.”5
Williamson acknowledged ten other people who contributed to his PNAS publication, including Lynn Margulis, who is reportedly responsible for ushering his paper past the normal front door review process. These contributors must have known about, and perhaps may share, Williamson’s reservations over the standard neo-Darwinian story of selection of mutants.
Williamson’s doubts are also shared by five additional researchers, who recently wrote in the Proceedings of the Royal Society, “Frustratingly, relevant fossils are still comparatively rare, most transitions have yet to be documented in detail and the mechanisms that underpin such events, typified by rapid large scale changes and for which microevolutionary processes [responsible for certain specific, slight variations] seem insufficient, are still unclear.”6
Williamson’s ideas would predict that those creatures that came from hybridogenesis ought to have larger genomes today, since they would represent the combination of separate genomes. The rebuttal paper by Hart and Grosberg stated that Williamson’s thesis was “astonishing and unfounded.” They pointed out, for example, that some of the largest insect genomes are found among those that Williamson would not attribute to hybridization. Thus, they concluded that “there is so far no evidence” supporting hybridogenesis. They also re-asserted the existence of “abundant empirical evidence for the evolution and loss of larval forms by natural selection.”3
Beneath the veneer of a controversial peer-review process is a substantial debate over the very basics of evolution. Some scientists have pointed out that neo-Darwinism is inadequate to explain why life forms appear fully-equipped, unique, and discrete. One of these bravely offered hybridogenesis as an alternative evolutionary mechanism. Others cogently demonstrated some scientific deal-breakers for hybridogenesis. Perhaps both sides are correct in their assessments of the opposing evolutionary ideas—neither explanation is sufficient. And if life could not have evolved, it must have been created.
- Matson, J. 2009. Controversial caterpillar-evolution study formally rebutted. Scientific American. Posted on scientificamerican.com October 29, 2009, accessed October 29, 2009.
- Williamson, D. I. Caterpillars evolved from onychophorans by hybridogenesis. Proceedings of the National Academy of Sciences. Published online before print August 28, 2009.
- Hart, M. W. and R. K. Grosberg. Caterpillars did not evolve from onychophorans by hybridogenesis. Proceedings of the National Academy of Sciences. Published online before print October 30, 2009.
- See Thomas, B. Darwin’s Evolutionary Tree ‘Annihilated.’ ICR News. Posted on icr.org February 3, 2009, accessed October 29, 2009.
- Lawton, G. 2009. Why Darwin Was Wrong About the Tree of Life. New Scientist. 2692: 34-39.
- Lü, J. et al. Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proceedings of the Royal Society B: Biological Sciences. Published online before print October 14, 2009.
* Mr. Thomas is Science Writer at the Institute for Creation Research.
Article posted on November 5, 2009.