Evolutionary Cul-de-Sacs: Ferns Debunk Another Evolutionary Principle
“The principle of the evolutionary cul-de-sac is commonly invoked to explain the apparent lingering existence of once-diverse groups of organisms,” writes Torsten Eriksson in the April 1 issue of Nature.1 “Maybe that principle itself has had its day.”
The case in point are ferns, which long had been thought to have been pushed into an evolutionary dead end by flowering plants (angiosperms). Eriksson’s comments are in response to a research paper on fern diversity in the same issue by Schneider et al.2:
Some biological concepts keep popping up, even when they have been shown, time and again, not to be generally true. One well-known example is the ‘biological species concept’, the idea that only those organisms that can cross and produce fertile offspring belong to the same species. This can’t generally be true for many reasons, the most obvious perhaps being that some organisms are not even sexual (such as bacteria and dandelions) and yet have species.
Schneider et al. (page 553 of this issue) touch on another of these favourite concepts, the ‘evolutionary cul-de-sac”. This is a common explanation for why some groups that show great diversity in the fossil record still exist but are greatly diminished in diversity, remaining largely unchanged – and supposedly unable to change. The new findings tell us that ferns, at least, do not belong in this category. Schneider et al. conclude that ferns (Fig. 1) have attained their current diversity much more recently than had been thought, and they probably did so as a response to the diversification of flowering plants.
So rather than getting pushed aside, ferns actually flourished within the ecosystem invaded by the “newer” flowering plants. Schneider’s international team based their conclusions on molecular data and a re-evaluation of the fossil record, because “a full understanding of trends in fern diversification and evolution using only palaeobotanical evidence is hindered by the poor taxonomic resolution of the fern fossil record in the Cretaceous.”
So instead of being squeezed out by competition, Eriksson imagines that the rapidly-diversifying angiosperms caused ferns to undergo “an evolutionary reawakening”, making “a variety of habitats that could be explored by opportunistic organisms.” This seems the opposite of earlier Darwinian and Malthusian assumptions. “Perhaps the whole idea of the evolutionary cul-de-sac is basically flawed,” he concludes.
1Torsten Eriksson, “Evolutionary biology: Ferns reawakened,” Nature 428, 480 – 481 (01 April 2004); doi:10.1038/428480a.
2Schneider et al., “Ferns diversified in the shadow of angiosperms,” Nature 428, 553 – 557 (01 April 2004); doi:10.1038/nature02361.
So another evolutionary principle has been debunked by evolutionists. Wonderful. Keep up the good work.