Science of how fins morphed to fingers found in new evolution study

Despite Charles Darwin’s revolutionary, “On the Origin of Species,” evolutionary biologists still don’t have a rationale for how the physical transformations occurred. But in a new study published yesterday, researchers sourcing technology that didn’t exist in the mid-nineteenth century have potentially discovered a mysterious link, a “cellular and genetic connection between the fin rays of fish and the digits of tetrapods,” the classification of all four-limbed vertebrates.

The elusive explanation follows Darwins observations in which he said: “The bones of a limb might be shortened and flattened to any extent, becoming at the same time enveloped in thick membrane, so as to serve as a fin; or a webbed hand might have all its bones or certain bones, lengthened to any extent, with the membrane connecting them increased, so as to serve as a wing; yet all these would not tend to alter the framework of the bones or the relative connection of the parts.”

In the study, featured in the journal Nature, scientists from the University of Chicago described through three years of experiments how they used “novel gene-editing techniques and sensitive fate mapping to label and track developing cells in fish.” The research paper’s contents detail  “. . . how the small flexible bones found at the ends of fins are related to fingers and toes, which are more suitable for life on land.”

Co-author, Neil Shubin, in a released statement said, “For years, scientists have thought that fin rays were completely unrelated to fingers and toes, utterly dissimilar because one kind of bone is initially formed out of cartilage and the other is formed in simple connective tissue. Our results change that whole idea. We now have a lot of things to rethink.”

Tetsuya Nakamura, fellow co-author of the study, used the novel CRISPR/Cas9 gene editing technology “to delete important genes linked to limb-building” in the zebrafish used for the study “and then selectively bred zebrafish with multiple targeted deletions.” High energy scans revealed “that fish lacking certain genes lost fin rays,” which are the bones in a fish fin that are dermal contrary to human fingers, which are made of cartilaginous bones. Nakamura also found, nonetheless, that “the small bones made of cartilage fin increased in number” in the fish.

Another contributing member of the study, Andrew Gherke, observed particular embryonic cells migrate as the animals developed. He said, “It was one of those eureka moments. … We found that the cells that mark the wrists and fingers of mice and people were exclusively in the fin rays of fish.”

Source: International Business Times

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