Evolution: a different view with loss of traits; not Behe (Introduction)

by David Turell , Friday, September 23, 2022, 19:15 (581 days ago) @ David Turell

From Quanta website:

https://www.quantamagazine.org/by-losing-genes-life-often-evolved-more-complexity-20200...

“'And that was the start of my frustration,” said Cañestro,... His team was unable to find certain genes within Oikopleura’s genome that should have been there because they are very conserved across animals. In particular, none of the genes involved in the synthesis, modification or degradation of retinoic acid were present. Nor was the receptor for retinoic acid. Yet retinoic acid signaling was thought to be essential for making a brain, nerve cord and other vital features. Furthermore, Oikopleura also lacks a gene that seemed critical for triggering the development of heart tissue.

"'We found a situation in which the things we thought were essential are not there, even though the structure [they make] is still there. And that makes you rethink the essentiality of some of the genes.”

"Two surprising analyses that appeared in Nature Ecology & Evolution early this year have hammered home just how inessential genes can be, and how creatively evolution can deal with losing them. By analyzing hundreds of genomes from across the animal kingdom, researchers in Spain and the United Kingdom showed that a startling degree of gene loss pervades the tree of life.

"Their results suggest that even early animals had relatively complex genomes because of an unprecedented spurt of gene duplication early in life’s history. Later, as lineages of animals evolved into different phyla with distinct body plans, many of their genes began to disappear, and gene loss continued to be a major factor in evolution thereafter. In fact, the loss of genes seems to have helped many groups of organisms split away from their ancestors and triumph over new environmental challenges.

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"But in reality, the majority of gene losses during evolution are likely to be neutral, with no fitness consequences for the organism, says Michael Hiller, an evolutionary genomicist at the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden, Germany.

"The reason is that evolutionary gene losses often occur after some change in the environment or behaviors makes a gene less necessary.

***

"One of the best examples of adaptive gene loss in animals can be seen in cetaceans (the order of aquatic mammals including whales and dolphins), which have lost 85 protein-coding genes seen in other mammals, as Hiller reported last year. Many of these losses are probably neutral, but some seem linked to diving-related adaptations, like the narrowing of blood vessels during diving. One of the lost genes, KLK8, is interesting because it is involved in the development both of sweat glands in the skin and of the hippocampus in the brain; cetaceans lost it during their transition from land back to water. The loss of this gene is linked to the development of a thicker epidermis and the loss of hair (hair is not adaptive in aquatic environments, where it creates drag and does not preserve body heat as it does in terrestrial animals). (my Bold)

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"Dolphins and whales, Old World fruit bats, and elephants — three lineages with relatively big brains — have all lost a gene, HMGCS2, required for ketogenesis, a metabolic process that scientists had thought was required to support the activity and growth of large, energy-hungry brains. Brain cells consume glucose, but when that is unavailable, they fuel themselves with ketone bodies from fatty acids. HGMCS2, the enzyme that converts fatty acids into ketone bodies, becomes especially important during fasting.

***

"More generally, the pervasiveness of gene loss in the tree of life points to an inversion of a classic theme in evolutionary developmental biology. In the 1970s and ’80s, “the big shock was to find that flies and humans use the same genes,” Cañestro said. Replace the fly Pax6 gene with the human version, and the fly can still make an eye. “Now we are finding that sometimes the structures [that grow] are the same, but the genes responsible for making the structures have many differences,” he said. “How is it possible that there are so many different genes, and still the structures are the same? That’s the inverse paradox of evo-devo.'”

Comment: we here know all this about trait loss. They didn't note Behe's articles and book. Maybe Behe is persona non grata as a renowned ID'er. And note the 85 gene loss to go aquatic