About 360 million years ago, our fishy ancestors moved from water to land. Along the way, their fins turned into feet, with toes. And hundreds of millions of years later, the front pair evolved into hands.
To understand this profound evolutionary transformation, scientists have spent decades studying the fossils of extinct fish that sported limb-like fins. They have also compared the embryos of modern-day fish and land vertebrates to understand how their fins and limbs develop.
Now the precise DNA-editing technology known as CRISPR is letting scientists reconstruct this ancient evolutionary change in molecular detail. It turns out that hands and feet were not the products of new genes doing new things. Rather, through natural selection, pieces of old genetic recipes for ancient body parts were cobbled together into new combinations.
“It’s much easier than if you had to build from scratch,” said Aurélie Hintermann, a postdoctoral researcher at the Stowers Institute for Medical Research, in Kansas City, Mo.
On Wednesday, Dr. Hintermann and her colleagues showed just how old some of those pieces were: The recipe for building hands was borrowed in part from the one for our nether regions.
Dr. Hintermann and her colleagues carried out their study by tracing the activity of genes in developing embryos. An embryo begins as a fertilized egg with a single set of genes; it then divides into new cells, each of which inherits those same genes. But along the way, the cells turn these genes on and off in different patterns, enabling them to become particular tissues and organs. The cells also send out molecules that trigger neighbors to change their own genetic melody.
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