Evolution: only genetics can design a bush of life (Introduction)

by Balance_Maintained , U.S.A., Tuesday, September 25, 2018, 21:10 (2250 days ago) @ David Turell

A new study on a very simple group of animals can sort out relationships only by use of genetics. Phenotype cannot work and must be discarded:

https://www.quantamagazine.org/worlds-simplest-animal-reveals-hidden-diversity-20180912/

"The world’s simplest known animal is so poorly understood that it doesn’t even have a common name. Formally called Trichoplax adhaerens for the way it adheres to glassware, the amorphous blob isn’t much to look at. At just a few millimeters across, the creature resembles a squashed sandwich in which the top layer protects, the bottom layer crawls, and the slimy stuffing sticks it all together. With no organs and just a handful of cell types, the most interesting thing about T. adhaerens might just be how stunningly boring it is.

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"But after spending four years painstakingly reconstructing the blob’s genome, Eitel might know more about the organism than anyone else on the planet. In particular, he has looked closely enough at its genetic code to learn what visual inspections failed to reveal. The variety of creature that biologists have long called T. adhaerens is really at least two, and perhaps as many as a dozen, anatomically identical but genetically distinct “cryptic species” of animals. The discovery sets a precedent for taxonomy, the science of naming organisms, as the first time a new animal genus has been defined not by appearance, but by pure genetics.

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"Ever since its discovery in the late 1800s, T. adhaerens has been recognized as having a highly unusual body plan, and it has formally had the phylum of Placozoa (“flat animals”) to itself for almost half a century. Just one level more specific than kingdom, a phylum is a cavernous space to occupy alone: Our phylum, Chordata, overflows with more than 65,000 living species ranging from peacocks to whales to eels. Biologists have long suspected that Placozoa hid more diversity, and mitochondrial evidence strengthened that suspicion in 2004, when researchers found that short sequences from different individuals looked about as different as those of organisms from different families (one level more general than genus).

'But that observation about the two Placozoa didn’t meet the accepted international standards for putting them in new taxonomic categories, which have historically been based on animals’ forms. “At the time we had just uncovered the genetic differences,” said Allen G. Collins, a co-author of the 2004 paper.

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" When the team finally had a full genome ready for comparison, the payoff turned out to be worth the wait. “We expected to find differences, but when I first saw the results of our analyses, I was really overwhelmed,” Eitel said.

"A quarter of the genes were in the wrong spot or written backward. Instructions for similar proteins were spelled nearly 30 percent differently on average, and in some cases as much as 80 percent. The Hong Kong variety was missing 4 percent of its distant cousin’s genes and had its own share of genes unique to itself. Overall, the Hong Kong placozoan genome was about as different from that of T. adhaerens as human DNA is from mouse DNA. “It was really striking,” Eitel said. “They look the same, and we look completely different from mice.”

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"By comparing the Placozoa variation with the average genetic differences between groups in other phyla, the German team concluded that the Hong Kong Placozoa qualified as not only a new species, but also a new genus.

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"The team gave their specimen the genus name Hoilungia, for a shapeshifting dragon king from Chinese mythology, and they named the species hongkongensis, for where it was collected. Similar genome-based classifications are common in the protist and bacterial worlds, and a relative handful of cryptic animal species have been named based on genetics. Namings (and renamings) that blend morphological characters with genetic ones, which recently re-classified a common houseplant, are also growing more common. But this was the first time genetic characters alone, unsupported by features like beak size or fin number, had been used to define an animal genus. “These people did the whole thing from the sexy molecular biology all the way to the proper naming,” said Susanne Renner, a botanist at the Ludwig Maximilian University. “It’s just great.”

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"Renner says this work is the latest step in an ongoing shift toward genetic taxonomy. “It took a long time to take off and now it’s taking off,” she said. She points out that in contrast with the pages of text that can go into a formal description of a species, specifying an organism with just four letters as the German team has done lends itself to snappy efficiency. “Linnaeus would be happy to do it. He was envisioning very brief and sharp diagnoses.'”

David: Comment: It occurs to me that this revolution in classification might help better define the whale series and perhaps explain the the pattern of change, by using fossil DNA, as has been dome in researching human origins. But what I can predict is the branches of the bush will be changed.

Personally, I think they will have a long, hard haul trying to make any sense out of the results unless they let go of common descent.

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What is the purpose of living? How about, 'to reduce needless suffering. It seems to me to be a worthy purpose.