Darwin Comes to Town: How the Urban Jungle Drives Evolution

Darwin Comes to Town: How the Urban Jungle Drives Evolution by Menno Schilthuizen

At the close of his exploration of the somewhat oxymoronic “urban nature,” Menno Schilthuizen tells us that one of his aims is that “the urban organisms you see on your daily wanderings of the city streets will  become more special, more interesting, worthy of more than a casual glance.” Schilthuizen, I’d say, is more likely to succeed than not in achieving his goal, as Darwin Comes to Town: How the Urban Jungle Drives Evolution (2018) is a delightfully informative whose insights are enthusiastically and clearly conveyed.

Schilthuizen loses no time in introducing us to a different way of viewing our noisome, concrete and metal cityscapes, opening up with a description of how:

the inner city, for all its hustle and bustle and thoroughly unnatural appearance, becomes a constellation of miniature ecosystems … Here a snapdragon growing in wild profusion from some invisible crack … The emerald veins of moss sprouting from slits between cracked reinforced glass … Feral rock pigeons …

Though we tend to think of cities as barren wastelands, not “of” nature but nature’s antithesis, Schilthuizen does yeoman’s work in opening our eyes to the bounty of life in it, above it, under it: insects, birds, mammals, reptiles, amphibians.

If that were all, Darwin Comes to Town would be a nice enough catalog of the world at our feet (or above our heads). But the subtitle of the book is How the Urban Jungle Drives Evolution. And this is where things get truly fascinating, as Schilthuizen points out that much as we think of evolution as occurring at a glacial pace (literally), “it can actually be observed here and now.” And the book is rife with such examples, beginning with the Culex molestus, the London Underground mosquito, which over the London Tube’s relatively blink-of-an-eye existence, has become genetically diverse across different tube lines, which act as islands would. Mosquitoes in different lines are genetically different from one another and from their brethren above. The underground insects feed on humans, not birds, mate in small numbers rather than large swarms, and do not hibernate, since the temperature is always tolerable. They have adapted to their human-created environments — our human presence is now forcing evolution on a grand and shockingly fast scale.

After some background on the massive growth in urbanization and loss of the wild (a sad stat: “each year the average distance between a given point on the map and the nearest forest increases about 1.5%”), we’re treated to a host of other examples of adaptation and possible speciation. We get non-native catfish who have learned to hurl themselves out of shallow water to latch on to non-native pigeons. We learn of the myriad of ways urban birds are different from their relations in the country — raising their birdcalls to a different pitch and calling at different times of the day so as to be better heard against the city soundscape, becoming better problem/puzzle solvers, becoming less risk-averse. We revisit a classic example of the idea of human-forced evolution — the peppered moth — and follow its rollercoaster ride of acceptance — skepticism — acceptance. We learn how pigeons in the city are better able to deal with poisonous metals, similar to a tiny fish, the mummichong, that lives in water that is so polluted it would kill most other marine creatures. In all these cases, Schilthuizen is very careful not to generalize or oversell, precisely characterizing, for example, the difference in the examples between learned/adaptive behavior and true genetic speciation.

Along the way we explore how the modern world is driving everything toward greater homogeneity thanks to the spread of non-natives and increased urbanization. Nearly half of urban life, he tells us, is non-native and much of it is becoming the same kind of life — the same insects, the same birds, the same plants, all “inching toward a single globalized multi-purpose urban biodiversity.”

Darwin Comes to Town is both wildly fascinating and at times depressing, as it can feel a bit like whistling past the graveyard or finding what comfort one can in what we’re doing to the world. But it’s impossible to resist Schilthuizen’s enthusiasm and sense of wonder. And toward the end he opens both up even more speculatively as we consider ways in which we can do some actual design or engineering into our cities to incorporate some of what we’re learning — building green roofs for instance, or not putting in life-corridors to allow the isolated pockets of creatures to continue to diverge from their common ancestry. It’s a good conclusion to an excellent book, leaving us to think not just of the impact we’ve had but the impact we could have if we were just a bit more thoughtful and purposeful about things. Not a bad thing to ponder as we, thanks to Schilthuizen, look with a bit more wonder at the nature-we-don’t-think-of-as-nature around us.