If one were to push the rewind button, erase life’s history and let the tape run again, the results would be completely different. So goes evolutionary biologist Stephen Jay Gould’s metaphor for the evolutionary process.1 Biological evolution should not repeat itself. And yet scientific advance, including a new study of salamanders, continues to demonstrate that evolution does “repeat” itself.
Chance superimposed onto history—that is, historical contingency—governs biological evolution. Evolution should not be repeatable, since every evolutionary pathway consists of thousands of unlikely events, each one funneling the process down a unique avenue.
Detecting contingency in the biological realm stands as a key test for the evolutionary paradigm. If scientific investigation finds chance at work in biological systems, the theory of evolution gains powerful support. On the other hand, the evolutionary paradigm receives a significant challenge if evolution seems to generate recurring (“repeatable”) results. The application of new techniques, based on advances in molecular biology, has provided just such a challenge to the evolutionary paradigm. Researchers have uncovered several examples of “repeatable evolution.”2
Relying on DNA sequence information rather than physical characteristics for comparisons, evolutionary biologists have discovered repeatable evolution for Anolis lizards, ranid frogs, cichlid and stickleback fish, river dolphins, mangabey monkeys, and island plants. And now scientists from UC Berkeley studying tropical salamanders have just discovered another example of repeatable evolution.3 This new discovery shows that the phenomenon of repeatable evolution can be properly viewed as a characteristic feature of the biological realm.
Four genera of lungless salamanders (members of the family Plethodontidae), suited for an underground lifestyle (fossorial), live in the lowland tropical region of southern Mexico and northern South America. These salamanders possess an elongated body and dramatically shortened limbs. One genus of lungless salamanders, Lineatriton, is comprised of a single species, Lineatriton lineolus. Based on external morphological features, biologists classified L. lineolus as a member of the genus Oedipina. However, detailed studies of internal anatomy later revealed fundamental differences, placing L. lineolus in a separate genus. Recent mitochondrial (mt) DNA analysis conducted by the UC Berkeley students supports this classification of L. lineolus.
In addition to supporting the reclassification of L. lineolus, the recent mt DNA analysis uncovered an unexpected result. L. lineolus is not a single species, but actually two separate species thought to have evolved independently to produce a unique combination of traits that serve as an extreme specialization for a fossorial lifestyle¾at least according to the evolutionary paradigm. Mitochondrial DNA analyses indicate that specimens from different regions of L. lineolus’ geographical range are more closely related to separate species belonging to the lungless salamander genus Pseudoeurycea than to each other. For L. lineolus, repeatable evolution seems to have occurred at two levels: 1) convergence with Oedipina; and 2) parallel evolution to produce two morphologically indistinguishable species.
The widespread occurrence of “repeatable evolution” strikes a blow at chance––the essence of the evolutionary process. However, the same data fits beautifully into a creation model. The repeated occurrence of unrelated organisms possessing trait combinations needed for survival in a particular ecological niche points to “repeated creation” rather than to evolution. It’s not surprising that a single Creator would reuse the same good design more than once to bring into existence organisms perfectly suited for their environment.
- Stephen J. Gould, Wonderful Life: The Burgess Shale and the Nature of History (New York: W. W. Norton, 1989), 48-51.
- Fazale R. Rana, “Repeatable Evolution or Repeated Creation?” Facts for Faith 4 (Q4 2000), 13-21.
- Gabriela Parra-Olea and David B. Wake, “Extreme Morphological Homoplasy in Tropical Salamanders,” Proceedings of the National Academy of Sciences, USA 98 (2001): 7888-91.