(excerpted from Amy Maxmen, “Evolution: A can of worms” Nature 470, 161-162 (2011), cited in "Evolution Running Backwards", Creation-Evolution Headlines, February 2011), also cited in Creation Matters, a publication of Creation Research Society, Volume 16, Number 1, January/February 2011, to appear at http://www.creationresearch.org/creation_matters/pdf/2010/CM15%2006%20low%20res.pdf)
|A marine worm in the |
But a recent report published in Nature is causing scientists to rethink the storyline. It is titled Acoelomorph flatworms are deuterostomes related to Xenoturbella . The study by an international team of researchers, who used new analytical techniques and data, removes acoel worms from their position near the trunk of animal evolution and instead places them closer to vertebrates.
The rearrangement of the tree of life has triggered protests from evolutionary biologists, who are alarmed that they may lose their key example of that crucial intermediate stage of animal evolution.
If acoels do fit within the deuterostomes, the worms must have evolved from an ancestor with a central nervous system, a body cavity and a through-going gut that connected an anus and mouth. So researchers would need to explain how acoels and Xenoturbella lost those and other characteristics. They would also be left to search for another primitive-looking lineage that represents the evolutionary step between jellyfish-like animals and bilaterians. If one even exists.
"I will say, diplomatically, this is the most politically fraught paper I've ever written," says Max Telford, a zoologist at University College London and last author on the paper. "This means that we have no living representative of this stage of evolution: the missing link has gone missing."
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