Evolution: comb jelly neurons different from all others (Evolution)

by David Turell , Saturday, April 10, 2021, 21:02 (1321 days ago) @ David Turell

Not convergent, totally different:

https://www.quantamagazine.org/comb-jelly-neurons-spark-evolution-debate-20150325

"According to traditional evolutionary biology, neurons evolved just once, hundreds of millions of years ago, likely after sea sponges branched off the evolutionary tree. But Moroz thinks it happened twice — once in ancestors of comb jellies, which split off at around the same time as sea sponges, and once in the animals that gave rise to jellyfish and all subsequent animals, including us. He cites as evidence the fact that comb jellies have a relatively alien neural system, employing different chemicals and architecture from our own. “When we look at the genome and other information, we see not only different grammar but a different alphabet,” Moroz said.

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"But new support for Moroz’s idea comes from recent genetic work suggesting that comb jellies are ancient — the first group to branch off the animal family tree. If true, that would bolster the chance that they evolved neurons on their own.

"The debate has generated intense interest among evolutionary biologists. Moroz’s work does not only call into question the origins of the brain and the evolutionary history of animals. It also challenges the deeply entrenched idea that evolution progresses steadily forward, building up complexity over time.

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"To make up for our inability to see into the past, scientists use the morphology (structure) and genetics of living animals to try to reconstruct the relationships of ancient ones. But in the case of comb jellies, the study of living animals presents serious challenges.

"Little is known about comb jellies’ basic biology. The animals are incredibly fragile, often falling to pieces once they’re caught in a net. And it’s difficult to raise them in captivity, making it nearly impossible to do the routine experiments that scientists might perform on other animals.

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"Scientists hope that more data — including genomes of additional ctenophore species — will help resolve the deepest branches of the animal tree. And that, in turn, could have profound implications for our understanding of neurons and where they came from. “The branching order has a major influence on how we interpret the evolution of the nervous system,” said Gáspár Jékely, a biologist at the Max Planck Institute for Developmental Biology in Germany."

Comment: I've skipped all the confused discussion. This is an odd branch, not really c compatible with common descent.