Serenely incubating eggs in the inner city, this bird had little in common with its shy, reclusive ancestors that nested in Europe’s forests. Early in the 19th century, probably in Germany, blackbirds began settling in cities. By the mid-20th century, they were hopping around on stoops all over Europe.The rapid evolution of animals living in cities is a hot topic in biology these days. In North America, studies have shown that urban raccoons are measurably smarter than their wild cousins, since they live in an environment where food is plentiful but danger comes in hundreds of forms. (My sons are fascinated by this news and like to imagine raccoons evolving into clever goblins living around and among us, stealing our stuff.) There are moths that have evolved to avoid street lights and plants specialized to grow in cracks in the pavement. I wonder what is happening to North American robins, which now nest almost entirely in suburbs.
Many “wild” bird species — like the peregrine falcons, red-tailed hawks and laughing gulls of New York — have set up camp in cities. But the thing about Europe’s urban blackbirds (a relative of the American robin, not to be confused with North American blackbirds, which belong to a different family) is that they are very different from their forest-dwelling relatives. They have stockier bills, sing at a higher pitch (high enough to be heard over the din of traffic), are less likely to migrate (in cities there’s food and warmth year-round), and have less nervous personalities.
For many of these differences, genes are responsible. The birds’ DNA, after 200 years or less of adaptation, has diverged from that of their rural ancestors.
And, for that matter, to us.
"My sons are fascinated by this news and like to imagine raccoons evolving into clever goblins living around and among us, stealing our stuff."
ReplyDeleteI'm not quite certain that's the stuff of imagination rather than the present reality.
"I wonder what is happening to North American robins, which now nest almost entirely in suburbs.
And, for that matter, to us."
In the past two centuries or so of modern cities? Well for one thing, we've gotten taller, for a variety of reasons.
For another thing, we've developed sanitation, which has radically changed both the microbes we live among (and which live within us), and changed our own genetic spectrum by allowing a greater variety of individuals survive to reproduce, rather than die of things like cholera, measles, et cetera.
We've also altered our diets radically, going from the necessity of all food being grown locally, to being able to import food of all sorts from all over the world. This has changed which crops we cultivate (and even led to the extinctions of a few species and the extirpations of a great many), and once again broadened our own genetic pool.
Speaking of importing food, that's only possible because of modern transportation, the development of which is directly tied to the rise of modern cities. And yet again, that broadened our genetic diversity greatly, as now people can move over oceans and between continents in the course of hours rather than weeks, allowing people who otherwise would never have met to have children together.
There are probably a lot of other things too. We've probably become more noise tolerant on a heriditary level, for example. We've probably become less susceptible to acrophobia, claustrophobia, and agoraphobia. We've almost certainly become more sensitive to the presence of pests and vermin, particularly insects and the like, likely making arachnophobia more common. We don't live amongst livestock anymore, so cross-species infection rates have gone down, possibly reducing our immunity to said diseases. Et cetera.