From National Geographic:
“It’s a paradox,” said Leonid Moroz, a neurobiologist at the University of Florida in Gainesville and lead author of a paper in today’s Nature about the biology of the comb jelly nervous system. “These are animals with a complex nervous system, but they basically use a completely different chemical language” from every other animal. “You have to explain it one way or another.”
The way Moroz explains it is with an evolutionary scenario—one that’s at odds with traditional accounts of animal evolution.
The earliest animals, according to this new theory, had no nervous system at all. The cells of these early animals could sense their environment directly, and could send signals directly to neighboring cells.
Millions of years later, those signals and receptors became the raw material for the nervous system. But its evolution, according to Moroz, took place in two separate lineages. One led to today’s ctenophores. The other led to all other animals with nervous systems—from jellyfish to us.
Ctenophores have long vexed taxonomists. Their resemblance to jellyfish earned them a spot on the tree of life as a sister group to cnidarians (the phylum that includes jellyfish). On the basis of their nervous systems — which can detect light, sense prey and move musculature — many researchers had them branching off from the common ancestor of other animals after the sponges and flattened multicellular blobs known as placozoans, neither of which have a nervous system. Now armed with data showing that ctenophores lack many common genes, some scientists contend that these are the closest living relatives to the first animals.
Paper. Open access. From Abstract:
Although two distinct nervous systems are well recognized in ctenophores, many bilaterian neuron-specific genes and genes of ‘classical’ neurotransmitter pathways either are absent or, if present, are not expressed in neurons. Our metabolomic and physiological data are consistent with the hypothesis that ctenophore neural systems, and possibly muscle specification, evolved independently from those in other animals.
And here some of us had thought that plants, not animals, would be the death of simple-minded accounts of evolution.
See also: Probably no solution to problems of evolution will work if information is ignored. But that would mean dumping current materialism.
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