Monday, March 23, 2015
In an essay titled "The
Rise and Fall of the Living Fossil", Ferris Jabr argues that, "The
idea that some species are relics that have stopped evolving is
finally going extinct." Jabr focuses on the crocodile for most of the
piece, noting some of the errors that have resulted from the idea:
Intrigued by this puzzle, a post-doctoral research fellow at the University of Washington named Jamie Oaks began collecting DNA samples from all 23 living crocodilian species, comparing sections of the genome where mutations were most likely to have appeared. Although the fossil record had confirmed that ancient crocodilians were more diverse than previously realized, it also demonstrated that, on the whole, crocodilians were not particularly swift evolvers compared to mammals and other vertebrates. Even accounting for this slower-than-average evolution, Oaks did not find nearly as many differences between the modern crocodilian genomes as one would expect had those species diverged all the way back in the Cretaceous. He concluded that modern crocodilian species split from their last common ancestor between 8 and 13 million years ago, not long before ancient hominins split from their last common ancestor with chimpanzees. The living fossil theory of crocodiles had overestimated their evolutionary age by about a factor of 10.Jabr's piece relays fascinating details as to how this idea was shown to be false in the case of crocodiles, and it provides interesting historical background on both how the idea arose from Darwin's "fanciful" phrase and how it and other notions shape popular conceptions of evolution.