Dollo's law of irreversibility

Dollo's law of irreversibility (also known as Dollo's law and Dollo's principle) is a hypothesis proposed in 1893^[1] by French-born Belgian paleontologist Louis Dollo which states that evolution is not reversible. This hypothesis was first stated by Dollo in this way: "An organism is unable to return, even partially, to a previous stage already realized in the ranks of its ancestors."^[2] According to this hypothesis a structure or organ that has been lost or discarded through the process of evolution will not reappear in exactly the same form in that line of organisms.^[3][4] According to Richard Dawkins, the law is "really just a statement about the statistical improbability of following exactly the same evolutionary trajectory twice (or, indeed, any particular trajectory), in either direction."^[5] Stephen Gould viewed the idea less strictly, suggesting that "irreversibility" forecloses certain evolutionary pathways once broad forms have emerged: "[For example], once you adopt the ordinary body plan of a reptile, hundreds of options are forever closed, and future possibilities must unfold within the limits of inherited design."^[6]

Proposed mechanism

A recent study on the evolution of protein structure proposed a new mechanism for this effect. It examined a hormone receptor that had evolved from an ancestral protein that was able to bind two hormones to a new protein that was specific for a single hormone. This change was produced by two amino acid substitutions, which prevent binding of the second hormone. However, several other changes subsequently occurred, which were selectively neutral as they did not affect hormone binding. When the authors tried to revert the protein back to its ancestral state by mutating the two "binding residues", they found the other changes had destabilised the ancestral state of the protein. They concluded that in order for this protein to evolve in reverse and regain its ability to bind two hormones, several independent neutral mutations would have to occur purely by chance with no selection pressure. As this is extremely unlikely, it may explain why evolution tends to run in one direction.^[7]

Proposed exceptions to Dollo's law

It is readily observed that many taxa of gastropods have reduced shells, and some gastropods have even lost the coiling of their shell during the evolutionary process.^[8] According to Gould's interpretation of Dollo's law, it would not be possible to re-gain a coiled shell after the coiling has been lost. Nevertheless, a few genera in the family Calyptraeidae may have changed their developmental timing (heterochrony) and gained back (re-evolution) a coiled shell from an uncoiled limpet-like shell.^[8][9] Other exceptions to this law include the wings of stick insects,^[10] the larval stages of salamanders,^[10][11] lost toes in lizards,^[12][13] and clavicles in non-avian theropod dinosaurs.^[14]

Also, a recent study on the evolution of the mandibular teeth of the frog Gastrotheca guentheri proposed its teeth have re-evolved using genetic structures already present, instead of re-evolving a whole new tooth blueprint.^[15][16] Dr. John Wiens, who teaches in the Department of Ecology and Evolution at Stony Brook University, N.Y., studied the jaws of modern tree frogs for several years and compared them to fossils and DNA of over 170 amphibian species. He found that Gastrotheca guentheri, a species of tree frog native to Colombia and Ecuador, grew back teeth that had been “evolved away” millions of years ago.^[17]

The evolution of the peppered moth over the past 250 years also gives one pause when considering Dollo's Law.

See also

• Entropy and life
• Irreversibility
• Fitness landscape
• Devolution (biological fallacy)

References

1. ^ Dollo, L (1893). Les lois de l'évolution. Bull. Soc. Belge Geol. Pal. Hydr, VII:164-166.
2. ^ Dollo, quoted in "Evolution: Ammonites Indicate Reversal," in Nature, March 21, 1970
3. ^ Goldberg, Emma E; Boris Igić (2008). "On phylogenetic tests of irreversible evolution". Evolution 62 (11): 2727–2741. doi:10.1111/j.1558-5646.2008.00505.x. PMID 18764918. 
4. ^ Collin, Rachel; Maria Pia Miglietta (2008). "Reversing opinions on Dollo's Law". Trends in Ecology & Evolution 23 (11): 602–609. doi:10.1016/j.tree.2008.06.013. PMID 18814933. 
5. ^ Dawkins, Richard (1996) [1986]. The Blind Watchmaker. New York: W. W. Norton & Company, Inc.. ISBN 0-393-31570-3. 
6. ^ Gould, Stephen J. [1993] (2007) "Eight little piggies," Vintage Books. ISBN 978-0-099-50744-4
7. ^ Bridgham, Jamie T.; Eric A. Ortlund, Joseph W. Thornton (2009). "An epistatic ratchet constrains the direction of glucocorticoid receptor evolution". Nature 461 (7263): 515–519. doi:10.1038/nature08249. ISSN 0028-0836. PMID 19779450. 
8. ^ ^{a b} Collin, R.; Cipriani, R. (2003). "Dollo's law and the re-evolution of shell coiling". Proceedings. Biological sciences / the Royal Society 270 (1533): 2551–2555. doi:10.1098/rspb.2003.2517. PMC 1691546. PMID 14728776. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1691546.  edit
9. ^ Pagel, M. (2004). "Limpets break Dollo's Law". Trends in Ecology & Evolution 19: 278. doi:10.1016/j.tree.2004.03.020.  edit
10. ^ ^{a b} Chippindale, P. T. and J. J. Wiens. (2005). Re-evolution of the larval stage in the Plethodontid salamander genus Desmognathus. Herpetological Review 36(2) 113.
11. ^ Marshall, C. R., et al. (1994). Dollo's law and the death and resurrection of genes. Proc Natl Acad Sci USA 91 12283.
12. ^ Galis, F., et al. (2010). Dollo's law and the irreversibility of digit loss in Bachia. Evolution 64(8) 2466.
13. ^ Davies, E. Frogs re-evolved lost lower teeth. BBC News. January 31, 2011. Retrieved February 9, 2011.
14. ^ Paul, Gregory S (2002). Dinosaurs of the Air: the evolution and loss of flight in dinosaurs and birds. CJHU Press. p. 10. ISBN 0801867630. 
15. ^ Wiens, J. J. (2011). "Re-Evolution of Lost Mandibular Teeth in Frogs After More Than 200 Million Years, and Re-Evaluating Dollo's Law". Evolution 65 (5): no. doi:10.1111/j.1558-5646.2011.01221.x.  edit
16. ^ Bhanoo, S. A. Marsupial tree frog evolved to regain the teeth its ancestors jettisoned. New York Times February 8, 2011. Retrieved February 9, 2011.
17. ^ By Andy Polhamus. "Stony Brook Professor Discovers 'Re-Evolution' in Frogs". Stony Brook Independent. [1]

External links

• The Loom: Recoil From Dollo's Law
• Dollo's Law and the Death and Resurrection of Genes