I can remember the first time I saw a Cerulean Warbler.
When I moved to the city of Chicago many, many years ago, it was the heart of winter. I spent a number of hours a month in the conservatories of Chicago, and the Lincoln Park Conservatory convinced me to train as a docent in the spring. Instead of training for the Conservatory, however, I trained to be a docent at the Alfred Caldwell Lily Pool, an absolute jewel of historic landmark near the lake in Lincoln Park. It was a great fit for me, a young man excited about science communication who loved talking about plants, animals, and ecology, with a bit of history, architecture, and sociology to boot. It was a near perfect fit.
Being a park on the lakeshore, we attracted more than just local runners or lost tourists looking to enter the zoo. As soon as we opened in the spring, we started to be visited by birders. Birders are some of the best people on the planet at encouraging curiosity. If you see a person in a Chicago Park near the lake with a pair of binoculars, you can probably ask them what they’ve seen, and they’ll tell you as much as you’re willing to hear. These birdwatchers explained to me that Chicago is on a migratory bird pathway, a trail that leads birds who summer and nest in the Northern United States and Canada to and from their winter homes in the tropics and around the Gulf of Mexico.
As I mentioned, the Cerulean Warbler was a treat for me. It’s a bright blue fellow that, to me, seemed to embody the concept of the blue-bird of happiness. But there are a lot of birds to get excited about. The relatively common American Redstart is a nice burst of orange and black when we’re just getting used to the new color of green in the spring. Ruby Crowned Kinglets and Golden Crowned Kinglets teach us about appreciating the beauty of subtle differences in tiny birds. Seeing an American Kestrel is a treat as well as a lesson that just because something is adorable doesn’t mean that it’s not a stone-cold killer. If you follow our Twitter, you know my love of ducks. Seeing a hooded merganser, goldeneye, and teal all in the same day is a hat trick I’ve only pulled off once. And some of my favorites aren’t rare, but still exciting to see; we might not be Capistrano, but seeing the lake full of Barn Swallows in the spring fills my heart with joy.
It wasn’t well into my graduate studies in genetics that I started to appreciate how impressive these birds are at helping us understand human development. One of our best model organisms (organisms that we study often because they tell us a lot of information and are easy to take care of with established protocols) for developmental biology is the chicken, an organism that has been raised by humans for millennia for food. During early development, the chicken embryo is incredibly similar to the human embryo. Chickens develop gills during an early stage of development, reflecting a period in their evolutionary history where their ancestors were not yet terrestrial. This happens in human development, too. At some point, you had gills. And a tail. Let that bit of information blow your mind.
One of the most fascinating parts of the development of chickens is that the intricacies of development are controlled by a handful of genes called hox genes. Hox genes are genes (regions of DNA that encode for a molecule that has a specific function like a protein or a reactive nucleic acid) that encode for a protein in the homeobox family. Homeobox genes bind to a region of DNA upstream of genes needed for the development of multicellular organisms as they develop. Thus, homeobox genes are a set of genes that control the expression of a series of other genes. That control other genes. That sometimes control even further genes. The initial switches that are hox genes work in a particular order, with some genes only active in what will be the feet, some only active in what will be the lower back, some only in the abdomen, some only in the arms/wings, and so on and so forth. And to make things even crazier, they are kept in the same order in the genome. The genes line up like a map of the body, with one end of the genes defining a chicken’s tip, one end defining a chicken’s tail.
We use model organisms to help learn about ourselves. And it turns out, the order of these genes in a chicken that determine the uppermost controls of development is not unique to the chicken, but nearly universal in all animals. These genes are also in the right order and doing the same high level of control in each of us humans as we develop. And in mice. And in fruit flies. They’re in almost every animal we look at, and all in the same order in our genomes (total of all DNA in each cell) defining tops from our bottoms.
Birdwatching is fun because of how diverse the bird species that fly through Chicagoland are. We have warblers, larks, towhees, tanagers, orioles, swallows, swifts, herons, cranes, egrets, creepers, nightjars, hummingbirds, gulls, terns, ducks, geese, owls, hawks, sparrows, and even the ridiculously cute house wren. It’s migratory bird season right now, so rush out to our lakeshore parks and keep an eye out for a migrating olive warbler or a piping plover. When you see them, remember that all of these birds start looking almost identical, and the first steps of them going from egg to fully form bird are using almost the same genes that lead from us going from zygote to adorable baby. Hox genes in a bird turn on genes that can lead to wings, feathers, and delicate legs and bones, while in people those genes turn on genes that lead to fingers, toes, and our opposable thumbs. It’s in these details, in the cascade that these same switches initiate, that allow us to differentiate into the vast diversity that we here in Chicago are uniquely able to see. Happy birdwatching, Chicago!