platypus feet considered flippers or paws

But in 2013, he heard about a new gene-editing technique called CRISPR, which could modify and delete genes with unparalleled ease and precision. He had wanted to do that for years, but never had the right tools for the job. To confirm what he was seeing, he needed to do the fish version of that classic French experiment with mice: delete the relevant Hox genes and see what happened. “It ran counter to everything we thought.” So, when Shubin looked at Gehrke’s image, he wasn’t expecting to see that the fin rays were red. Instead, they either evolved from some small bones in the fleshy base of the fin, or were a totally new evolutionary innovation with no predecessors. So scientists, Shubin included, believed that our hands and digits did not evolve from fin rays.

The long, thin, parallel bones in the rest of the fin-the fin rays-look metaphorically like fingers, but they’re made from a different kind of bone, and they grow in a totally different way. But there’s nothing that quite matches your hands and fingers.

The fleshy base contains several bones that are related to those in your arms. Think about a fish’s pectoral fin-the one that sits behind its head. What about a zebrafish? Which part of its fin would turn red? Shubin had some very specific expectations. In mice, this method only paints bone-making cells in the wrist-all of these cells, and only these cells, go on to build the bones of hands and digits. To find out, Gehrke used a technique that automatically adds glowing red molecules to any cell that activates Hoxa13-essentially, painting them for easy identification. What do those fishy genes do? “It ran counter to everything we thought.” He knew that the legs of mice and other four-legged animals evolved from the fins of fish, and he knew that fish have counterparts of Hoxa13 and Hoxd13. No digits.įor Shubin, that discovery was thrilling. When they deleted these genes, rodents would grow up with limbs that ended in stumps. In 1996, French scientists showed that two genes in this group-Hoxa13 and Hoxd13-control the development of hands and feet in mice. And they have counterparts in many different animals: the head-building Hox genes of flies are related to those of mice, which suggests that most animals rely on a common toolkit of body-building genes that we all inherited from a shared ancestor. They line up in orderly rows, so that those that coordinate the building of heads sit ahead of those that dictate the sculpting of tails. They conduct the opera of animal growth, telling other genes when and where to activate, to build the right organs in the right place. To understand Shubin’s confusion and delight, you first need to know about a group of genes called Hox. “I thought I understood what was going on, and I clearly didn’t,” he says. But Gehrke’s picture told him that he had got one aspect of limb evolution drastically wrong. He has discovered groundbreaking fossils, published umpteen scientific papers, written best-selling books, and filmed award-winning documentaries on the subject. He remembers where he was when his student Andrew Gehrke showed him a picture of a fish fin.įor many years, Shubin has studied how ancient fish took their first steps onto land, and how their fins evolved into our arms and legs.

Some people remember where they were when they were told Kennedy had been assassinated, says Neil Shubin.

Platypus feet considered flippers or paws