DOLLOS LAW AND THE DEATH AND RESURRECTION OF GENES

Dollo's law, the concept that evolution is not substantively reversibl e, implies that the degradation of genetic information is sufficiently fast that genes or developmental pathways released from selective pre ssure will rapidly become nonfunctional, Using empirical data to asses s the rate of loss of coding information in genes for proteins with va rying degrees of tolerance to mutational change, we show that, in fact , there is a significant probability over evolutionary time scales of 0.5-6 million years for successful reactivation of silenced genes or ' 'lost'' developmental programs. Conversely, the reactivation of long ( >10 million years)-unexpressed genes and dormant developmental pathway s is not possible unless function is maintained by other selective con straints; the classic example of the resurrection of ''hen's teeth'' i s most likely an experimental artifact, and the experimental reactivat ion of the Archaeopteryx limb developmental program has been shown to be a misinterpretation. For groups undergoing adaptive radiations, los t features may ''flicker'' on and off, resulting in a distribution of character states that does not reflect the phylogeny of the group,