Evolution, visible on a branch near you
What could be a more ordinary sight than the robin, the red-breasted bird that hops around on the ground, yanking worms out of the dirt? Go out with a bunch of birdwatchers on a cold day near dawn and you’ll hear a sigh of disappointment when a bird in the distance turns out to be a boring old robin.
But Arkhat Abzhanov, associate professor of organismic and evolutionary biology at Harvard University, wonders: Have you ever really looked at a robin? What shape is its beak? What about its head?
Abzhanov, who studies the evolution of birds, sees the 10,000 species that fill our world—including some of the most ordinary ones—as a major opportunity to probe deep questions about both evolution and developmental biology.
“What I think is the most interesting thing about birds is we see them everyday and we’re so used to them,” he said. “ And very few people realize just how unusual these animals are. ... How do we go about studying something like this, that looks normal to us, but is in many ways unusual?”
Start, he suggests, by really giving the robin a close look. Take the beak: it’s easy to think of a beak as a primitive triangular appendage that opens and closes; a standard part that can be pencilled into a child’s drawing. But Abzhanov calls it “the ultimate tool” and a source of amazing diversity and specialization in the bird world, from pelicans to finches. After all, it has to make up for the arms and fingers that ancestors of birds could have used to manipulate objects.
The robin beak, he said, doesn’t have a lot of depth, because it doesn’t need much strength. It is straight, because it’s used to pluck worms out of the dirt. In contrast, he said, finches have a very deep bill, which they can use to crack hard seeds. Other birds need long beaks to allow them to retrieve nectar from flowers. Understanding beaks, and how the different ones came about, can give scientists specific insight into the genetic process that happens as birds develop in the egg.
“The argument is all the birds, including robins, are using the same development program, but they tweak it in different ways to build different beaks,” Abzhanov said.
In the laboratory, Abzhanov uses genetic tricks to make chicken embryos develop different types of beaks. The chicken (which, he adds, is another underappreciated bird) can develop the beak of a bullfinch, Abzhanov said, or a robin simply by simple genetic tweaks. Those, in turn, can provide insight into how birds became so diverse and specialized—with some birds cracking open seeds like a nutcracker and others sticking their strong beaks into a seed and breaking it open.
On a recent bird walk in Mount Auburn Cemetery, I saw white-winged crossbills silhouetted against the sky; birds that were distinguishable to an amateur like me only because of the curious way their bills hook in opposite directions, crossing over one another. I asked Abzhanov about those odd bird beaks, and he delightedly told me it was a question he was interested in probing further—there were a few red crossbills, he said, in his laboratory freezer.
But the basic story, as far as it’s understood today, is already pleasingly weird: crossbills, he said, are born with normal, straight beaks. But before they fledge from their nest, they develop a kind of “handedness” to their beak, based on how they bite their food as chicks. They tend to favor one side of the jaw more than the other, he said, eventually developing a dominant right or left beak. Sometimes, the right upper bill crosses over the left; sometimes the opposite occurs.
Then, they use those beaks to fish nutritious seeds out of round coniferous cones, using their curving beaks to get seeds that would be inaccessible to other birds.
Abzhanov plans to both demystify bird biology more, and conjure a bit of mystery about the ones we take for granted, at a talk called “What art thou, little bird?” at the Harvard Museum of Natural History on Thursday, Jan. 31 at 6 p.m.