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More Troubles in the Tree of Animal Life

In late 2005, three biologists published a study in Science which concluded, “Despite the amount of data and breadth of taxa analyzed, relationships among most [animal] phyla remained unresolved.”

In 2008, the relationships among animals are still controversial. A recent news release at Science Daily highlights a new study, “Tree Of Animal Life Has Branches Rearranged.” The story reports, “The study is the most comprehensive animal phylogenomic research project to date, involving 40 million base pairs of new DNA data taken from 29 animal species.”

According to the article, the study yielded surprising results: “Comb jellyfish — common and extremely fragile jellies with well-developed tissues — appear to have diverged from other animals even before the lowly sponge, which has no tissue to speak of. This finding calls into question the very root of the animal tree of life, which traditionally placed sponges at the base.”

This is the common theme among systematists trying to produce a grand “tree of life”: Similarities between different types of organisms commonly pop up in places they shouldn’t. Such unexpected similarities were found in this study, forcing one of the scientists to conclude “either that comb jellies evolved their complexity independently from other animals, [or] sponges have become greatly simplified through the course of evolution.”

This study has its own conclusions–but are they the final word? In the past decades, the tree of life has been re-arranged innumerable times. If history is to be our guide, it is likely that future studies will contradict the findings of this study.

The fundamental problem for neo-Darwinism is that phylogenetic trees based upon one gene or characteristic will often conflict with trees based upon some other gene or characteristic. This is why I discussed recently how morphology-based trees commonly conflict with DNA-based trees. Many studies (like this one) thus use many genes in hopes to avoid the conflicts between trees based upon individual genes or proteins. They must use this method because some genes are telling the wrong phylogenetic story; by averaging out the genetic signals, the theory says that you’ll find the true phylogenetic history.

But using this many-gene method might be like someone who asked for directions to Atlantis, but failed to find the lost continent after trying to follow the directions. So instead they asked 50 people for directions to Atlantis, expecting that any conflicts and contradictions in their various bits of advice will all average out, and by combining their accounts — pass the river, go 50 stadia — wait no 45 stadia, then left at the canyon — no then right, then paddle for 3 days towards the north star — no you paddle 2 days west — and you’ll somehow find Atlantis. The other possibility is that there is no Atlantis to find and that people are mistaken in their various theories about how to find Atlantis.


Casey Luskin

Associate Director, Center for Science and Culture
Casey Luskin is a geologist and an attorney with graduate degrees in science and law, giving him expertise in both the scientific and legal dimensions of the debate over evolution. He earned his PhD in Geology from the University of Johannesburg, and BS and MS degrees in Earth Sciences from the University of California, San Diego, where he studied evolution extensively at both the graduate and undergraduate levels. His law degree is from the University of San Diego, where he focused his studies on First Amendment law, education law, and environmental law.



Tree of Life