Darwin Comes to Town

Menno Schilthuizen begins Darwin Comes To Town: How the Urban Jungle Drives Evolution, his jaunty romp through current theories about evolution in cities, by taking his readers on a hunt for an underground mosquito. That’s correct—there is now a mosquito who lives underground, ready to bite a relatively new species—the subway traveler.  As well as being vaguely creepy, this is interesting to Schilthuizen because the underground mosquito is, for all intents and purposes, an urban novelty. There were no underground mosquitoes before there were subways.  But soon after humans built subways, a certain strain of mosquitoes figured out how to lurk down inside their tunnels, ready to dine on a conveniently predictable food source.  For Schilthuizen, this is big news—a prime example of our urban existence driving evolution forward.

It’s important that we study city-driven ecology like this, Schilthuizen argues, because, in point of fact, the world is more urban than it’s ever been before. Our densely built environments, contrary to being the opposite of nature, are themselves sites that spur evolution forward in surprising ways; often more quickly than we thought possible.  Schilthuizen who once wrote a book about what scientists now know about the evolution of genitalia, likes asking us to explore what’s hidden in plain site. That book was called Nature’s Nether Regions— and it examined how evolutionary forces act on the very forms and shapes by which we propagate our species to begin with. In that book, Schilthuizen argued that scientists need to lift the cultural blinders that prevent them from studying something so (if you will) seminal. In this case, he’s also reminding to shift our gaze, in this case to the world directly proximate to us. Because our cultural biases make it counterintuitive to call the city “nature,” science has often pruriently avoided studying the city in favor of examining the so-called wild. But Schilthuizen wants us to be looking close to home: at the very real ecosystems and habitats we create and live within daily.

It’s not all glamorous, and not all lovely. The underground mosquito is a case in point. In other cases, the fieldwork is painstaking—Schilthuizen tells the story of a couple who spent 30 years under freeway underpasses documenting the way cliff swallows build nests there. They showed how, within a few generations nesting in this new “urban cliff” the swallow’s wing morphology adapted to allow it to rise more quickly off surfaces and thus avoid accidents with oncoming traffic.   There’s the cliff swallow, living alongside us, and actually adapting to traffic, freeways, trucks, the whole new structures we’ve built.

Indeed, when we look, even at freeways, it turns out there’s a lot to see. Another story features two bobcat populations that are separated by LA freeways and have already developed two different sorts of immune responses to stress caused by living in urban areas and amid local pesticides.  Evolution and adaptation are not distant– they are happening now, in our tunnels, near our onramps. In story after story, Schilthuizen shows these forces at work in backyards and suburban gardens and near urban bicycle racks.

How quickly can birds bugs butterflies and even bobcats adapt to patchier habitats, urban gardens, even toxins? What makes some animals more successful than others in adapting? This is an important question, and Schilthuizen does examine it, exploring ways that certain animals may be able to fit in more easily amid our noise. For birds, for instance, having a song that is not drowned out by urban noise is useful. Other birds succeed by finding habitat that mimics the places they once lived, like the cliff swallow. And some, like the bobcat, actually develop some resistance to formerly toxic substances.

Yet for all that this book is both erudite and illuminating, Darwin Comes to Town, suffers, in the end, from its blithe approach.  For a world of birds with loud calls and toxin-resistant mammals itself sounds like far too low a bar too hope for. Nor is it really enough. Indeed, after discussing the marvelous ways that so many animals are adapting to human and urban life I felt certain that Schilthuizen would surely return to consider something of the plight of other beloved animals—the elephant say, or the sloth, or the cuckoo, or the tiger—who simply will not find a niche in tomorrow’s world metropolis.  I also thought that after discussing those animals who are able to adapt to the worst of our carcinogens, Schilthuizen would remind us of the many toxins that animals can’t avoid—and which we ourselves would cannot afford to consume either. But these reminders seem just outside the scope of the book, which leaves Schilthuizen’s celebration of urban evolution feeling laissez faire and even happy-go-lucky, perhaps to all of our detriment.

The take home message is this: building by building, road by road, toxin by toxin, we are building ecosystems. Each system we build can either be built with some version of health and coexistence in mind, or it can simply assume that all is well and we will be fine. Our challenge now is actually to articulate visions of ecosystems that sustain robust and diverse forms of life, and then to build them.

Indeed, Schilthuizen’s whole premise blurs the urban/nature divide—reminding us that everything is an ecosystem for something, even if it is an oil-filled puddle at the side of a stripmall. However, if that radical idea propels the book forward, I’d push the writer to be more explicit about leaning against another divide we humans seem to take for granted. After all, we too are animals. If urban spaces are changing the epigenes and genomes of animals that migrate to them,  they are changing us as well. One of my favoirite books last year was Peter Godfrey-Smith’s Other Minds,. In that book, which explores octopus intelligence, Godfrey-Smith makes a simple but important point:  the explosion of animal intelligences across species meant that all animal intelligence on earth evolved together. Our own primate intelligence is shaped by our relation with the intelligences of other animals, our strategies partly based on adapting and co-evolving with theirs. It is wonderful to see how some animals and organisms have adapted to and even flourish in our cities. But the massive industrial web that feeds our urban world imposes permanent change on habitats worldwide. In what way will we recognize and co-evolve with the animals that remain on the planet we share?

The question remains tantalizingly open.