Modern Genetics Confirms Evolutionary Relationship Between Fins and Hands

spotted gar

The spotted gar, an ancient freshwater fish species, provides genetic evidence for the evolutionary relationship between fins and hands. (Photo credit: blickwinkel/Hartl Alamy)

The news that hands evolved from fins is not a new one. In fact, fossil evidence in the form of Tiktaalik roseae, an ancient creature with characteristics of both fish and amphibians, confirms the connection.

“Fossils show that the wrists and digits clearly have an aquatic origin,” Dr. Neil Shubin, professor of organismal biology and anatomy at the University of Chicago, said in a press release. “But fins and limbs have different purposes. They have evolved in different directions since they diverged. We wanted to explore, and better understand, their connections by adding genetic and molecular data to what we already know from the fossil record.”

Shubin should know about the fossil evidence – he was the leader of the team that discovered Tiktaalik in 2004. Until recently, evolutionary biologists were having a hard time finding the structural equivalent to an autopod—that is, the structure that makes up a wrist and fingers or ankles and toes—in modern fish. Turns out, the scientists were studying the wrong kind of fish. While teleost fish (bony, ray-finned fish species) – which account for the majority of sport and commercial fish species – are well-studied, scientists found that they lack the genetic switches necessary to build wrists and fingers.

However, in research reported in the December 22, 2014 issue of the Proceedings of the National Academy of Sciences, scientists found that the spotted gar, an ancient (and still living) fish species, contained the genetic machinery necessary for the development of autopods. This species of freshwater fish, which is native to North America, split off from teleost fishes over 300 million years ago. When three gar gene switches related to fin development were inserted into developing mice, researchers noted that the resulting activity was almost exactly the same as the mice’s hand gene switches. In essence, the spotted gar provides genetic evidence for the evolutionary relationship between fins and hands.

“The genetic program to make wrists and digits is really, really ancient,” Andrew Gehrke, a graduate student at the University of Chicago and lead study author, said in a Washington Post article. “There are hypotheses that maybe some of these genetic switches evolved later on to create digits and wrists and what we know as hands. But our work shows these genetic switches are very, very old and present in ancient fish, and functioned in a really similar way [in all four-limbed creatures].”

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