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Humans’ most distant animal relative found

Researchers distinguished DNA of the comb jellyfish as the most distinct from humans’ in a recent study

The comb jelly — a shapeless, squishy blob that reflects the colors around it — may be our most distant animal relative, according to a study conducted by an international team of researchers that included Assistant Professor of Biology Casey Dunn. The study was published last month in the journal Science.

The study suggests the ctenophora, or comb jelly, is the animal most evolutionarily different from humans, rather than the sponge, which was previously thought to hold this title. Dunn said comb jellies “are like a distant cousin.”

Dunn and his team determined this relationship by extracting and analyzing the DNA from comb jellies and other animals, he said.

Though the comb jelly’s DNA is less similar to human DNA than that of sponges is, comb jellies have nervous systems, unlike sponges.

Dunn’s team discovered that comb jellies are missing many genes necessary to produce nervous systems, but interestingly still have them, he said.

“One way to explain this is that the nervous system evolved independently,” said Samuel Church ’15, who conducts research in the Dunn Lab.

“It was thought that (nervous systems) were so complex and could only evolve once,” Dunn said, but this research could show otherwise.

Sponges, which are now known to be more closely related to humans than comb jellies are, don’t have nervous systems, he said. There are two ways to account for this — it is possible that the comb jelly independently evolved a nervous system, but it is also possible that sponges lost their nervous systems over the course of evolution.

One way to resolve this ambiguity would be to see if sponges contain genes associated with developing a nervous system that is present in animals with nervous systems, Church said. “If these are found in sponges then we might think they once had the machinery for a nervous system, but they’re not making a nervous system now.”

This sort of research can be difficult “because it has been more than 550 million years ... since these splits happened,” Church added.

Dunn and his team are continuing their studies by doing more detailed analyses of the genomic data, Dunn said.

“We are also very interested in finding life on other planets to find out how nervous systems can form,” Dunn said. “My lab is very interested in answering the big questions.”

Church has been a member of Dunn’s lab since he was a first-year, and this past summer he did research in Norway with the lead author of the comb jelly study, Church said.

“I love the idea of figuring out the history of life on earth, the history of animals,” Church said. “And it’s really fun now that things like sequencing DNA (are) pretty inexpensive. It is really exciting to see these sorts of open questions get resolved. We get a lot of new answers as to how the world is organized.”



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