A sweeping new study tells a long genetic tale
If there’s a factory where birds are built, the workers were clearly smoking something the day they designed the hummingbird. And the ostrich. And the toucan. Imagine, too, the pitch meeting for the parrot, (“Let’s make this one talk!”), or the peacock (“So we got this crate of feathers…”).
Of course, that’s not how it really happened. Birds came along without our help, evolving from the Aves class into 23 orders, 142 families, 2,057 genera and finally 9,702 species—the most prolific speciation of all four-limbed vertebrates. The problem with such prodigious divergence is that it makes it hard to determine how the great bird explosion began in the first place. Now, however, in a pair of papers in Science, scientists report that they have an answer. Modern birds, they have learned, got their start like the universe itself—with something of a Big Bang, a burst of specialization that began 65 million years ago with the same asteroid hit that wiped out the dinosaurs and made room for mammals and other land animals.
This finding results from the work of hundreds of scientists at 80 labs and universities across 20 countries, done with the help of bird tissue collected from labs and museums around the world. Those specimens were sent to the Genome Tissue Institute in Beijing, where the basic sequencing was conducted. The first and most basic conclusion the investigators reached was a big one. “This confirms that there was a very rapid radiation and that major lineages of birds were in existence 5 to 6 million years after the extinction event,” says Joel Cracraft, an avian systemicist at the American Museum of Natural History in New York and a contributor to the papers. “They were very widely distributed as well.”
But there was much more to be learned, and that required the hundreds of others scientists to get busy parsing the genomes. A lot of their results live down in the technical weeds, where geneticists speak of such things as total evidence nucleotide trees and GTR+GAMMA models. Among the plain-English findings, however, there were some important top-line results. The investigators identified a sort of progenitor bird, for example, a so-called apex predator that came along shortly after the asteroid hit and was the great-great-great granddaddy of all extant land birds. The descendants that that founding father left can be connected in unexpected ways.
The gaudy flamingo and the proletariat pigeon turn out to belong to sister clades—or groups descending from one common ancestor. Similarly, there is a three-way kinship among the cuckoos; the bustards (medium-size game birds that include the paauw and its larger cousin, the straightforwardly named great paauw); and the turacos. The last group is a brilliantly colored and plumed family of birds that include the African banana eaters and the go-away birds, species that got their names because one of them, well, eats bananas and the other issues a warning call that sounds like it’s saying “go away,” which it sort of is.
Among the more granular discoveries, the investigators report that so-called vocal learners—birds with flexible repertoires of songs and mimicked speech—actually share some of their molecular brain structures with humans. And the very act of singing appears to change the birds’ epigenomes—the regulatory system that sits atop the genes and determines which ones are expressed—meaning that the more frequent the song the more specialized the bird’s genetic wiring will become.
But just in case the big, fun, colorful Aves class gets above itself, the papers do stress that every extant bird can trace its line back even further than the apex predator, all the way to a small and rather vulgar group of ancestors that are actually alive today; the saltwater crocodile, the American alligator and the Indian gharial—which is sort of an alligator with an absurdly skinny snout. For birds as much as for humans, it seems, no matter how high you climb, there are always a few embarrassing family members to keep you humble.