From: invalide@invalid.invalid   
      
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   https://archive.is/ffTZ1   
      
   How Did Hands Evolve? The Answer Is Behind You.   
      
   The evolutionary blueprint for hands was   
   borrowed in part from a much older genetic   
   plan for our nether regions, a new study   
   suggests.   
      
   ...   
   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.   
   ...   
   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.   
      
   Scientists have identified some of the locks that enable embryos of   
   humans and other species to grow limbs. In 2011, Denis Duboule, a   
   biologist at the University of Geneva, and his colleagues discovered a   
   half-dozen molecular locks sitting side-by-side along a stretch of DNA   
   called 5DOM. When 5DOM was snipped out of a mouse embryo’s DNA, the   
   embryo grew legs but failed to grow feet.   
      
   Dr. Duboule and his colleagues wondered how this crucial set of locks   
   evolved. Did it arise when our ancestors first came ashore and evolved   
   limbs? Or did it exist earlier, in our finned ancestors?   
      
   To tackle that question, Christopher Bolt, then a graduate student in   
   Dr. Duboule’s lab, searched through the genome of the zebrafish. He   
   discovered that it, too, had 5DOM.   
      
   Zebrafish and mammals share an ancient common ancestor that lived more   
   than 400 million years ago. The Geneva team’s discovery suggested that   
   this primordial ancestor already had 5DOM. And if it was still intact in   
   zebrafish, it must be doing something in their embryos. “It could not be   
   there by chance,” Dr. Hintermann said.   
      
   Dr. Hintermann, who took over the project while working in the Geneva   
   lab, grew zebrafish embryos from which she had removed the 5DOM locks,   
   using CRISPR. If the locks were important in the development of fish   
   fins, then deleting them might reveal how.   
      
   To her surprise, deleting 5DOM had little effect on the developing fins.   
   But it disrupted a region on the underside of the zebrafish’s tail,   
   where there are two openings: the anus, and a hole for the bladder and   
   for sexual organs.   
      
   This surprise prompted the researchers to take a closer look at the same   
   region in mouse embryos. Here they got a second surprise: 5DOM unlocks   
   the genes that built that region in mammals, too.   
      
   These and other experiments led the scientists to a new hypothesis for   
   the evolution of fingers and toes. The story starts a half-billion years   
   ago, with the earliest, simplest fish. Their bodies were little more   
   than heads connected to long-ribbon-like bodies; they swallowed food,   
   which made its way down a long digestive tract until the remnants   
   escaped through the anus. A nearby opening was used for sex, and the   
   release of urine.   
      
   The embryos of this protofish unlocked different genes to create the   
   different parts of its body. At the far end, 5DOM unlocked the genes for   
   the anus as well as the opening for its urethra and sexual organs.   
      
   That genetic recipe hasn’t changed in a half-billion years. That’s why   
   5DOM still controls the development of that region in both zebrafish and   
   mice — and us.   
      
   But about 360 million years ago, the scientists propose, 5DOM underwent   
   an evolutionary change. Now it could build not only our nether regions   
   but our fingers and toes, too.   
      
   Hands and nether parts might seem to have little in common, but there   
   are some key similarities. For one thing, both are extremities: In early   
   fish, 5DOM unlocked genes that determined the anatomy at the far end of   
   the body. In a developing limb, the fingers and toes develop at the far   
   end, too.   
      
   But Neil Shubin, an evolutionary biologist at the University of Chicago   
   and another author of the study, said that the precise evolutionary   
   changes that had given 5DOM its new job remain a mystery.   
      
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