In 1940 Thomas Wolfe’s posthumous novel, You Can’t Go Back Home, explored how brutally unfair the passage of time can be. In the finale, George Webber (the story’s protagonist) concedes, “you can’t go back home” to family, childhood, familiar places, dreams, and old ways of life.
In other words, there’s an irreversible quality to life. Most evolutionary biologists believe there is an irreversibility to the evolutionary process as well. In fact this idea is codified in what is called Dollo’s law, which states that an organism cannot return, even partially, to a previous evolutionary stage occupied by one of its ancestors. Yet, a number of recent studies, including one examining the reappearance of mandibular teeth in frogs, have uncovered what appears to be evidence for the violation of Dollo’s law.1 These violations raise questions about the validity of the evolutionary paradigm and at the same time add support for a creation model.
As a consequence of this principle, formulated in 1893 by the French paleontologist Louis Dollo, once an organ or structure is lost, it cannot reevolve in that particular evolutionary lineage.
Evolutionary biologist Richard Dawkins explains Dollo’s law this way:
Dollo’s Law is really just a statement about the statistical improbability of following exactly the same evolutionary trajectory twice…in either direction. A single mutational step can easily be reversed. But for larger numbers of mutational steps…mathematical space of all possible trajectories is so vast that the chance of two trajectories ever arriving at the same point becomes vanishingly small.2
If a biological trait is lost during the evolutionary process, then the genes and developmental pathways responsible for that biological system will eventually degrade, because they are no longer under selective pressure. In 1994, researchers from Indiana University determined that once a biological trait was lost, the dollo’s law at home with a creation model corresponding genes could be “reactivated” with reasonable probability over timescales of five hundred thousand to six million years. But once a time span of ten million years has transpired, unexpressed genes and dormant developmental pathways are permanently lost.3
In other words, the very nature of the evolutionary mechanism and the constraints of genetic mutations make it extremely unlikely that evolutionary processes would cause an organism to revert to an ancestral state or to recover a lost biological trait. You can’t go home again.
Violations of Dollo’s Law
Researchers have uncovered a number of recent instances in which it looks as if Dollo’s law has been violated. (It is beyond the space limitations of this article to describe these examples.) One such discovery includes the “reevolution” of mandibular teeth in the frog genus Gastrotheca.. When examined from an evolutionary framework, it is clear that mandibular teeth were present in ancient frogs and were then lost in the ancestor of all living frogs. It also looks as if teeth have been absent in frogs for 225 million years before they reappeared in Gastrotheca.
The author of this study, John Weins, reexamined eight other examples in which Dollo’s law was violated. In each he determined that the lost trait (which includes larval stages in salamanders and frogs, respectively, forelimb digits in lizards, eggshells in Boid snakes, and shell coiling in snails) reappeared after at least 20 million years and, in some instances, as long as 120 million years had passed. In the face of these surprising results, the author offered only speculation to account for the reevolution of the traits.
Violation of Dollo’s Law and the Theory of Evolution
Given that the evolutionary paradigm predicts that reevolution of traits should not occur, particularly after the trait has been lost for ten million years, the numerous discoveries of Dollo’s law violations provides a basis for skepticism. The problem is more than likely worse than it initially appears. Weins points out that such violations may be more widespread than imagined, but difficult to detect for methodological reasons.
Violation of Dollo’s Law and the Case for Creation
The seeming reappearance of the same biological traits––for example, mandibular teeth in frogs––could be understood as the work of the Creator. It is not unusual for engineers to reuse the same design or to revisit a previously used design feature in a new prototype. While there is an irreversibility to the evolutionary process, designers are not constrained in that way and can freely return to old designs. Such behavior reflects economy, elegance, and intelligence.