Stephen Jay Gould wrote Wonderful Life, a book in which he imagined the possibility of going back in time and replaying the evolution of life to see how closely it would resemble the original. Genetic changes are thought of as containing a stochastic element sifted by natural selection. The effects of natural selection would be influenced by environmental conditions. If the tape were run again with altered environmental conditions different results would be expected. A different set of random genetic events would change the tape. The logic is readily apparent.
Re-running scenes could be fun so if the tape of life were rerun what might we expect to see and is there anything we can do to in some small way simulate a forward/backward tape replay? Perhaps Henrique Teotnio and colleagues did replays of something much less gradiose but nevertheless useful as revealed in a Nature Genetics paper. But this is a contemporary movie and cites changes in the fruit fly (Drosophila melanogaster). The study was discussed in a blog entry titled Reverse evolution in real-time. Incidentally, this is an excellent blog IMO. Quoting from the linked piece:
The scientists used laboratory-grown populations of fruit fly (Drosophila melanogaster), derived from an original group of flies, harvested from the wild back in 1975. These ancestral flies were grown in the laboratory, for two decades, under different environmental conditions, (such as starvation and longer life-cycles) so that each population was selected for specific characteristics. Henrique Teotnio and colleagues placed these populations back in the ancestral environment, for 50 generations, to impose reverse evolution on the flies, and then looked at the genetic changes in certain areas of chromosome 3 of these flies.
Says Henrique, 'In 2001 we showed that evolution is reversible in as far as phenotypes are concerned, but even then, only to a point. Indeed, not all the characteristics evolved back to the ancestral state. Furthermore, some characteristics reverse-evolved rapidly, while others took longer. Reverse evolution seems to stop when the populations of flies achieve adaptation to the ancestral environment, which may not coincide with the ancestral state. In this study, we have shown that underlying these phenomena is the fact that, at the genetic level, convergence to the ancestral state is on the order of 50%, that is, on average, only half of the gene frequencies revert to the ancestral gene frequencies evolution is contingent upon history at the genetic level too'.
These findings provide further insights into the basic understanding of how evolution and diversity are generated and maintained. On the one hand, it provides evidence for evolution happening through changes in the distribution of alleles in a population (so-called standing genetic variation), from generation to generation, rather than the appearance of mutations, from one generation to the next. Conversely, as Henrique notes, 'It has implications for the definition of biodiversity: some of the 'reversed' flies appears to be phenotypically identical to the ancestral flies, but they are genetically different. How then do we define biodiversity?'.
Good question. Perhaps forward and reverse evolution can be engineered through adjustments of regulatory mechanisms. Constructing complex physical structures implies a logical sequence to the placement of physical components. For example, one would think a regulatory element would be preceeded by that which is regulated.
TP asked some questions recently in a comment.
Assuming scientists will be able to successfully reverse evolution in chickens, could the same techniques be used to fast-forward evolution?
Could such an effort provide evidence of front-loaded traits?
Fast-forwarding would be more problematic but rich in possibilities. My answer to TP's second question is yes. Genes that are indispensible in different pathways would be candidates.