Dollo's Law

Origins and meaning

In a short paper, Les lois de l'évolution (1893), Dollo argued that an organism cannot return to a former state and does not exactly repeat a state already realized. Gould (1970) interpreted Dollo's original intention not as a claim that evolution can never reverse direction but as a statistical claim that the chance of a complex state recurring identically by chance is vanishingly small. From a genetic standpoint, Muller (1939) held that traits involving many genes are difficult to reverse, and Simpson (1953) also accepted the principle as a general feature of macroevolution.

Genetic basis and counterexamples

Marshall, Raff and Raff (1994) calculated the rate at which unused genes are degraded by mutation and estimated that after about ten million years almost none of the genetic information needed to restore a lost trait remains. A series of counterexamples has since been reported, however. Whiting, Bradler and Maxwell (2003) argued that wings were lost and regained several times in stick insects, and Collin and Cipriani (2003) reported that coiled shells reappeared in a snail lineage with uncoiled shells. Wiens (2011) concluded that teeth in the lower jaw of frogs re-evolved in one lineage after being absent for more than 200 million years, and Lynch and Wagner (2010) argued that egg-laying re-evolved in a lineage of live-bearing boas.

Methodological debate and molecular irreversibility

Goldberg and Igić (2008) pointed out that such counterexamples can depend on the statistical methods used to infer trait changes on phylogenies and that tests of irreversibility must be handled carefully. Reviewing the counterexamples, Collin and Miglietta (2008) concluded that re-evolution is possible when the developmental pathway of a lost trait has been preserved for other functions. Teotónio and Rose (2001) discussed reverse evolution, in which traits return to ancestral states in laboratory populations. Bridgham, Ortlund and Thornton (2009) showed an epistatic ratchet in the evolution of a hormone receptor protein, in which later mutations block the path back to an earlier state, offering a mechanism for irreversibility at the molecular level. These ideas connect to the concept of path dependence.

FAQ

What is Dollo's law in simple terms?

Once a complex structure such as wings or teeth is lost during evolution, it is very unlikely to be regained in exactly the same form.

Has Dollo's law ever been broken?

Counterexamples such as stick insect wings, frog teeth and egg-laying boas have been reported, but conclusions can depend on the methods of analysis, so the debate continues.

Sources reviewed: 2026-10-26

References

1. Dollo, L. (1893). Les lois de l'évolution. Bulletin de la Société Belge de Géologie, de Paléontologie et d'Hydrologie, 7, 164–166.
2. Gould, S. J. (1970). Dollo on Dollo's law: Irreversibility and the status of evolutionary laws. Journal of the History of Biology, 3(2), 189–212.
3. Muller, H. J. (1939). Reversibility in evolution considered from the standpoint of genetics. Biological Reviews, 14(3), 261–280.
4. Simpson, G. G. (1953). The Major Features of Evolution. New York: Columbia University Press.
5. Marshall, C. R., Raff, E. C., & Raff, R. A. (1994). Dollo's law and the death and resurrection of genes. Proceedings of the National Academy of Sciences, 91(25), 12283–12287.
6. Whiting, M. F., Bradler, S., & Maxwell, T. (2003). Loss and recovery of wings in stick insects. Nature, 421(6920), 264–267.
7. Collin, R., & Cipriani, R. (2003). Dollo's law and the re-evolution of shell coiling. Proceedings of the Royal Society B, 270(1533), 2551–2555.
8. 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), 1283–1296.
9. Goldberg, E. E., & Igić, B. (2008). On phylogenetic tests of irreversible evolution. Evolution, 62(11), 2727–2741.
10. Bridgham, J. T., Ortlund, E. A., & Thornton, J. W. (2009). An epistatic ratchet constrains the direction of glucocorticoid receptor evolution. Nature, 461(7263), 515–519.
11. Collin, R., & Miglietta, M. P. (2008). Reversing opinions on Dollo's law. Trends in Ecology & Evolution, 23(11), 602–609.
12. Lynch, V. J., & Wagner, G. P. (2010). Did egg-laying boas break Dollo's law? Phylogenetic evidence for reversal to oviparity in sand boas. Evolution, 64(1), 207–216.
13. Teotónio, H., & Rose, M. R. (2001). Perspective: Reverse evolution. Evolution, 55(4), 653–660.