Evolution: more genomic evidence of pre-planning (Evolution)

by David Turell , Thursday, February 11, 2021, 15:58 (1163 days ago) @ David Turell
edited by David Turell, Thursday, February 11, 2021, 16:10

Fish had genes leading to land life:

https://www.sciencemag.org/news/2021/02/fish-had-genes-adapt-life-land-while-they-were-...

"Together, the studies suggest that in terms of genes, the aquatic precursors of four-limbed land animals, or tetrapods, were well-prepared. They were pre-equipped with genes that could be turned to making limbs, efficient air-breathing lungs, and nervous systems tuned to the challenges of life on land.

“'All these studies tell us that the origin of tetrapods was something waiting to happen,” says Borja Esteve-Altava, an evolutionary biologist at Pompeu Fabra University in Barcelona, Spain. Genetically, “Everything necessary was already there” before vertebrates came ashore, nearly 400 million years ago. (my bold)

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"In the trio of studies published last week in Cell, genes in living fish took the place of fossils as a way to peer back in time. One set of clues came from studies of mutagenized zebrafish, a favorite model for studying development. M. Brent Hawkins, then a Harvard University graduate student and now a postdoc, was shocked to discover zebrafish mutants with two bones resembling the forelimb bones of land animals in their front fins, complete with muscles, joints, and blood vessels. The finding is “quite spectacular,” says Marie-Andrée Akimenko, a developmental biologist at the University of Ottawa.

"Two mutated genes, vav2 and waslb, were responsible for the transformation. Both genes code for proteins that are part of a pathway controlling the activity of Hox11 proteins, regulatory molecules that guide the formation of the two forearm bones in mammals, among other functions.

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"Other genetic clues come from living representatives of ancient fish lineages. Only two groups of the lobe-finned fish are alive today: lungfish and coelacanths. About 400 million years ago, they diverged from the line of lobe-finned fish that gave rise to tetrapods 30 million years later.

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"The groundwork for terrestrial traits like limbs and lungs was laid deep in the fish family tree. Genes for such traits found in both lobe-finned and ray-finned fishes must also have been present in their common ancestor.

"None of the sequenced fish is on the precise branch that led to tetrapods. Yet all have much of the genetic equipment needed for life on land, including most of the genes and regulatory DNA needed to build limbs. For example, all the fish sequenced have a regulatory element that helps form synovial joints, which make fins and limbs flexible and are essential for terrestrial locomotion. The fish also have 11 genes that are needed to build lungs and that work the same way in the bichir’s lungs as they do in humans. One is for a pulmonary surfactant, a lubricating secretion that helps lungs expand and contract. Both the ray-finned fishes and the lobe-finned lungfish also apparently have a regulatory element that helps shape the right ventricle of the heart to deliver oxygen more efficiently.

"The findings show that “a lot of things we think are just in land animals are also in fish,” says Gage Crump, a developmental biologist at the University of Southern California. Finding all those genes in both lobe-finned and ray-finned fish means those genetic pathways must have been present in their common ancestor, some 425 million years ago. “It is surprising that some of these elements are so conserved for such a long evolutionary time,” Zhang says.

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"The genome of the lungfish offers a glimpse of later adaptations along the path to terrestrial life. It includes additional pulmonary surfactant genes that the ray-finned fishes lack, as well as DNA for specifying five toes, connecting nerves to limb muscles, and for sensitizing the brain to react fast. All those genes were previously thought to be unique to tetrapods.

"Putting it all together, Wang and Zhang think the transition to land involved three key steps. The ability to breathe air occasionally appeared in the common ancestor to ray-and lobe-finned fish, about 425 million years ago. Then surfactant genes, new nervous system genes, and other innovations enabled lobe-finned fish to leave the water temporarily. Finally, after the African lungfish split off from the lobe fins, the common ancestor of land vertebrates acquired other respiratory and locomotive refinements needed to live out of water.

"Rather than building new structures and genetic pathways just when vertebrates moved onto land, evolution apparently was thrifty, using existing genes to adapt to the opportunities offered by terrestrial habitats. “[The studies] show the extent to which the fish-tetrapod transition was achieved by modifying existing molecular systems, rather than creating new ones,” says Per Ahlberg, a paleontologist at Uppsala University."

Comment: note my bold, as science validates my theory that DNA is prepared for major advances. dhw sneers at my proposal that DNA has built-in planning for future major advances such as fish climbing into terrestrial life. This article is proof-positive the DNA setup for rapid advances is present. It explains the fossil gaps Gould tried to explain.