University of Chicago paleontologist Neil Shubin at the 2015 AAAS Annual Meeting | Atlantic Photography Boston
All humans have an "inner fish" lurking in their wrists and necks and eyes, one that Neil Shubin and his colleagues have discovered through fossils from the Arctic and from genes turning off and on in developing embryos.
In his plenary address at the 2015 AAAS Annual Meeting, the University of Chicago paleontologist and evolutionary biologist described what we know about the transition from finned fish to the first sprawl-legged land walkers. It's a transition, he said, that all humans still carry within their own limbs.
Shubin has shared this message with a broad audience through his popular science books and the PBS series "Your Inner Fish," which won the 2014 AAAS Kavli Science Journalism Award for in-depth television reporting.
"It's not just some esoteric event in the history of life," he said, "Every time you bend your wrist, every time you bend your neck, you can thank these fish living in water in the Devonian."
The late Devonian Period, stretching from about 385 million years ago to 358 million years ago, was the chapter in life's history when fish began to develop a body equipped for life on land. In his career, Shubin has gone from trailing the Pennsylvania Department of Transportation to examine new road cuts, to camping at the snowline in Canadian Arctic islands, in order to find the rocks that hold fossils from this time period.
In 2004, Shubin and his fellow scientists discovered Tiktaalik roseae, a spectacular example of a Devonian fish that still lived in water but showed signs of transitioning to dry land. It had fins and scales, but it also had a neck, eyes on top of its head, and traces of a wrist and arm bones.
All of these features were revealed gradually as Tiktaalik was removed from its rock casing one painstaking grain at a time. But today's paleontologist increasingly relies on "digital dissection," Shubin said. The fossils studied in his lab go through CT scans and other types of advanced image processing to zoom in on features in skulls that are sometimes less than a centimeter long. The researchers can now look deep into the tissue structure of ancient bone, or examine traces of blood vessel flow, or even digitally pry open Tiktaalik's flattened jaws to get a look at the formidable teeth of the predatory fish.
Shubin said that 3D printing is also making it possible to share their discoveries with more people all over the world. His team is in the process of putting the digital blueprints of their fossils online, "so that anyone — a student, a teacher, a researcher — can push a button and print out Tiktaalik," he said. "We're entering an age where you don't have to rely on a gatekeeper to study that fossil, you can use the Internet to study that fossil yourself."
Other researchers are tracing the development of limbs in the embryos of fish, mice, and humans by labeling and watching certain genes that turn on and off during embryonic development. The signs of your inner fish, Shubin said, are plain to see when scientists can look across species and find the genetic signatures of human wrist development inside a fish's fin using these methods.
Shubin has taught human anatomy to first-year medical students, "and it always surprised the students, to say the least, that the doctor teaching their human anatomy was a fish paleontologist," he said.
Eventually the students come to realize that "the basic roadmaps to understanding the biology of our bodies, and to devising applications for bettering our lives lie in other creatures," he said. "And the reason for that is because in every organ, every tissue, in every cell, in every gene in our bodies lies the footprint, the artifacts of three billion years of evolutionary change."