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Iffy Word Choice Challenges Dollo’s Law

April 4, 2013


Dollo’s Law states that “evolution is not reversible; i.e., structures or functions discarded during the course of evolution do not reappear in a given line of organisms” (Britanica). The law has been questioned for years but each result that “disproved” Dollo’s law was later looked at and understood using more recent technology and understanding of genetics to explain that it too was subject to the law.
Recent work with dust mites may be the first genetically checked evidence against Dollo’s Law. Scientists from the University of Michigan have constructed genetic phylogenies and have nearly conclusively determined that dust mites are from parisitc origin, and the parasites are in turn from free living origin. Dollo’s law would conclude that once the free living ancestors became parasites they would have lost the ability to be free living again, but the mites show that this is not the case.

The previous rebuttals of Dollo’s law has shown that it has two loopholes. The first occurs when complex, profound differences have simple genetic bases. The second, when phylogenetic patterns falsely indicate reversals. I’m not sure if I believe that the Michigan scientists have proved that either of these loopholes are not true, and therefore I believe it’s a bit too soon for the New York Times to publish an observation titled “A Challenge to Dollo’s Law.” While it is an interesting title that is sure to catch reader attention, it doesn’t seem to be very accurate. Even within the article the author mentions Dollo’s law but never allows for the loopholes.

The authors of the original paper “Is Permanent Parasitism Reversible?– Critical Evidence from Early Evolution of House Dust Mites” mention Dollo’s law claiming that they tested for irreversible evolution and found found that the dust mites have abandoned a parasitic lifestyle; however, the scientists don’t claim to have disproved Dollo’s law just that their species violates it. I would be curious to see further research testing the possibilities of the dust mites simply existing in a loophole, not disproving Dollo’s law entirely.

This type of reporting makes me nervous because if someone is to look at the headline, as I did, they might believe that Dollo’s law is being challenged in a way that has never happened before. The authors of the original paper mention that past studies rejecting Dollo’s law have turned up inconclusive. I feel that this challenge to Dollo’s law may be just as inconclusive because it may be difficult to prove that neither of the two loopholes occurred.

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