Darwin Comes to Town

by Menno Schilthuizen

  I also see some true cosmopolitan invaders, of the kind that ecologists call “supertramp species”: in the fields on campus grows tall fescue grass (Festuca arundinacea), originally from Europe, but now found on any lawn between the two poles (including the south lawn of the White House). And the walls of the moist bathroom in my rented apartment show the orange coloration of Aureobasidium pullulans, a fungus that forms one giant gene pool all over the world, continuously mixed by people carrying their toiletries from bathroom to bathroom.

  Such global homogenization of urban ecosystems is much more pervasive than these few anecdotal examples suggest. Urban ecologists worldwide are doing inventories that show clear evidence that unseen hands are causing cities worldwide to become communicating vessels for all manner of organisms. For example, an international scientific consortium that calls itself GLUSEEN (Global Urban Soil Ecology and Education Network) has recently carried out DNA surveys of soil microbes in cities and natural areas in Africa, North America, and Europe, and discovered that the species compositions of city soils across those continents are converging. At least for the 12,000 species of fungi and 3,700 species of a type of microbe called Archaea they found, the communities underfoot in cities were much more similar than in forests. And a team of researchers from the University of New Mexico used the information gathered by the nationwide American tradition of the Christmas Bird Count, where citizen scientists in thousands of locations count all birds in a 15-mile-diameter-circle in 24 hours. They discovered that cities as far apart as 2,500 miles still share about half their birds, while the avifaunas of natural areas that distant are almost complete different. Two German researchers, Rüdiger Wittig and Ute Becker, finally, did an analysis of the plants found growing around what they call Baumscheiben (tree disks), the small islands of soil around the base of street trees. Just like in the bird studies, a much greater proportion of the Baumscheiben-flora was shared by cities all over the continent, than by random Baumscheiben-sized plots in natural vegetation. Even in the American city of Baltimore, 80 percent of the herbs growing at the roots of street trees were identical to those found in the European cities.

  What all this means is that the ecosystems of cities around the world are growing more and more alike; their communities of plants and animals, fungi, single-celled organisms, and viruses are slowly inching toward a single globalized, multi-purpose urban biodiversity. And even if the exact species across cities may not be identical, you will find similar species playing similar roles. On my walks in Sendai, for example, I see the spider Larinioides cornutus weaving its webs near lights on bridges across the Hirose river. This is a different species from the European bridge spider (Larinioides sclopetarius) that Astrid Heiling observed doing the exact same thing on Viennese bridges across the Danube earlier in this book.

  The upshot is that each urban species, wherever it finds itself in the world, will encounter quite a similar set of urban cohabitants. In a previous chapter, we called these “urban encounters of the second kind”: the living cogwheels of a city’s ecological clockwork that can themselves also evolve. As those wheels in different cities converge, this will lead to similar evolutionary breakthroughs for comparable struggles for urban life all over the planet.

  But there is also homogenization in what I called earlier, “urban encounters of the first kind”: adapting to the physical and chemical signatures of the city environment. For those components of the urban environment, there are global, invisible connections as well. Over recent years, the visionary urban scientist Marina Alberti of the University of Washington has been revealing this process, which she calls “telecoupling.” As I interview her over Skype she first explains where she is coming from: “Yes, I am an urban planner, but my background is complex and I have studied biology as well.” She is rooted, she says, in the idea that humans are fully part of nature. “My work has tried to challenge both ecology and urban planning since both still see humans as separate from ecological systems.”

  She continues: “Cities are networked far beyond their own physical edges.” What she means is that cities exchange not only species, but also the human inventions that make those cities tick and that urban organisms must adapt to. Take artificial lighting at night (ALAN), for example. Over time, one light innovation after another has swept across the world, leapfrogging from city to city. First there was gas light, then incandescent lamps, followed by high-pressure sodium, mercury vapor, and now, LED lights. Each of those types has a different light spectrum, and ecologists such as Kevin Gaston in the UK and Kamiel Spoelstra in the Netherlands are finding out that nocturnal animals respond differently to different spectra. So, if animals are indeed evolving to deal with ALAN, each lighting innovation will cause a new swing in their urban evolution. And since those technological innovations will spread rapidly from city to city, so will the evolutionary swings, either because the better-adapted animals themselves disperse between cities (like the pollution-adapted peppered moth did) or because the same solutions for the same problems evolve independently in different cities (like what seems to be going on in the city blackbirds, and in PCB-tolerant mummichog fish).

  Alberti envisages that such technological telecoupling among cities will apply to any innovation in transportation, road and train construction, architecture, green space planning, et cetera. All the more so, because cities worldwide are beginning to exchange information and undertake concerted action more enthusiastically even than the countries they are in. In his book, Connectography: Mapping the Future of the Global Civilization, global strategist Parag Khanna gives the example of the C40, a global network of megacities that work together to invent and implement solutions for climate change. “Because cities define themselves […] by their connectedness rather than their sovereignty,” Khanna writes, “one can imagine a global society emerging much more readily from intercity relations than international relations.”

  In other words, urban nature of the future could be a globally homogenized, dispersed ecosystem, inhabited by a dynamic but shared set of organisms that is constantly evolving, exchanging species and genes and innovations to deal with the new technologies with which humans equip their cities. Not that the urban ecosystems will ever be completely cut off from natural ecosystems: the wild will keep functioning as a source of pre-adapted species and genes that urban ecosystems may put to good use. Still, as the urban environment expands its reach, it will become more and more an ecosystem in its own right, writing its own evolutionary rules and running at its own evolutionary pace.

  These urban evolutionary rules and pace, Alberti points out, are beginning to diverge more and more from the ones we’re used to in the natural world. There, in the unspoiled forests, deserts, swamps, and dunes far from human interference, evolutionary change is driven by age-old natural forces. As wild ecosystems get larger and more complex, and niches get filled, fewer and fewer opportunities are left to exploit and evolution may slow down. But in cities, says Alberti, it is the other way around. The pace of evolution is set by ecological opportunities that emerge from human social interactions. The bigger and more complex cities get, the more intensive human social interactions will be, and the more rapidly the environment will change as a consequence—and telecoupling then ensures that these changes reverberate through the network of the world’s cities. In those pressure cookers of environmental change, species will need to speed up their evolution or become extinct.

  Some species, whose evolution cannot keep up with the frenetic rate at which the urban environment develops, will indeed drop out, but others will continue adapting and perhaps splitting into multiple species as humans pose them new obstacles or offer them new ways of living. In 2017, in the journal Proceedings of the National Academy of Sciences, a team of authors led by Alberti published a global analysis of more than 1,600 cases of “phenotypic” change (an alteration in the appearance, development, or behavior of a species, which may or may not be genetic). When they factored in a whole set of environm
ental “drivers” (some urban, some natural), they discovered what Alberti calls “a clear signal of urbanization.” The data showed that phenotypic changes in cities happen faster than those farther away from cities, and that the strongest drivers are encounters of the second kind (interactions with humans themselves or with other organisms brought into the city by humans).

  That leads us to a question that I alluded to in an earlier chapter: what about ourselves? Could we be evolving as well? After all, the urban environment is just as foreign to our bodies and minds as it is to house crows, knotweeds, and mummichogs. We have never lived under conditions even remotely like it for the hundreds of thousands of years that have shaped our evolution until now. Moreover, if there ever was a time that could produce the raw material for a new spurt in our evolution, it is today. Think about it: with nearly eight billion people on earth, and a quintillion sex cells produced in our bodies on a daily basis, there is a greater chance on new, crucial mutations appearing in our genomes now than there was when we still were an endangered species eking out a living in a few forgotten corners of the world. Are we humans perhaps evolving to suit our new urban environment just like all the animals and plants that we cohabit with? It’s an intriguing question, and one that we now have the tools to answer.

  Just like scientists scanned the genomes of peppered moths to pinpoint the mutation in the cortex gene that swept across the industrially revolutionized world in the nineteenth century, we can scan the genomes of an ever increasing number of people to detect how the human population has evolved in recent years. DNA technology is developing so quickly that it is only a matter of years before everybody will have their full genome as private information on a hard-disk and/or allow researchers to mine it for scientific information. But even with the modest amount of one million or so human genomes that researchers have access to today, they are picking up signals of ongoing human evolution.

  The UK10K and Biobank projects, for example, two UK-based initiatives to sequence the genomes of tens of thousands of Britons, have revealed that recent centuries have seen evolutionary changes in genes that link with height, eye and skin color, lactose tolerance, nicotine craving, head size in infants, hip circumference in women, and age at sexual maturity in women. Probably none of these evolutionary shifts has to do specifically with living in cities. But other researchers have found evidence for city-specific human evolution. For example, in parts of the world where urbanization began earlier, more people carry immune system genes that help fight tuberculosis. Organisms that cause or spread such diseases do so more easily where people are densely packed—even in today’s modern cities—and that will affect the evolution of our immune systems.

  Another titillating idea is that human sexuality will change. For millions of years, any human would meet only a few handfuls of possible partners in his or her lifetime. The average urbanite of today, however, runs into that many potential candidates during a walk around the block. That means more competition and a much more intensive sexual selection. Combined with perhaps a great-tit-like shift in perceptions of what makes a perfect (urban) mate, who knows how our sexual signals and preferences are going to evolve in the future?

  Having said that, for the foreseeable future, it is more likely that urban humans will be influencing the evolutionary trajectories of urban flora and fauna rather than the other way around. Alberti: “I think that the human species is changing the genetic makeup of the planet. We have both the responsibility and the opportunity to co-evolve with other organisms. Whether humans will take this challenge, I do not know.” Alberti formulates a challenge with great implications for how we are going to design and manage our urban environments. Can we harness the power of urban evolution and use it to make more liveable cities for the future?

  20

  DESIGN IT WITH DARWIN

  My daughter is much better at this sort of thing.

  I show up unannounced at the reception desk of Roppongi Hills, a grandiose “integrated property development complex” in the heart of Tokyo, asking if I can have a look at their famous green roofs. I get a glossy Roppongi Hills Town Guide and a cascade of apologies, but, no, very sorry, they are only accessible during “events” and special occasions. Despondently, I return to my daughter and girlfriend who are waiting outside. “But did you tell them you’re working on a book?” my daughter Fenna asks, and pushes me back inside. Her smiles and persistence, and my conjuring a collection of business cards and university IDs eventually result in the desk clerk phoning the company’s greens management office, but they, too, politely turn us down. Book or no book, you must file a special request.

  But Fenna is in a belligerent mood. “Let’s see how close we can get to it,” she suggests, and ushers me into the lobby of the neighboring Hyatt Hotel, where we sneak past the reception desk and into the elevator. For a few minutes we shuttle between floors until we find the one that approaches closest to the level where we expect the Roppongi Hills green roof. At the end of the carpeted corridor in which we find ourselves is a large window, which, as we approach it, opens up to a great vista. First, the hazy, jagged skyline of Tokyo comes into view. Then, the “town in the city” that is Roppongi Hills: a cluster of offices, shops, apartments, gardens, and a museum, interconnected by sculpture-lined paths. And, as we press our noses against the window and feel the urban heat radiating through the glass into the air-conditioned hotel air, there, right in front of us, in the blazing sun, lies the rooftop urban nature reserve we had been looking for.

  It’s as if a chunk of the Japanese countryside (that traditional mosaic of rice fields, forests, grassland, and ponds known as satoyama) has been dug up and plonked on top of the Keyakizaka building, where it sits like a green crown. A rice paddy and several meadows are fringed by cherry woodland and privet hedges. Walkways snake through them. There are lotus flowers in a pond and vegetable plots with bitter gourd, eggplant, and tomato. A resident in a sun hat is tending to her rice, while two jungle crows with bills like sushi knives are nibbling at the young cherries of the cherry trees. Then they take wing and flap toward the gigantic Mori Tower, looming high overhead. We watch them get smaller and smaller until eventually they are two dots that dissolve among the ledges of the top floors, where the Mori Building Company, who designed Roppongi Hills, has its headquarters.

  Since the early 1970s, Mori has been one of the leading building firms to incorporate vegetation into their architecture. The rooftop garden at Roppongi is modest, at only 1,500 square yards, but some entries in their portfolio have much larger surfaces covered with green. And they are not the only ones. In the city of Fukuoka, the Argentinian designer Emilio Ambasz created the project developer’s equivalent of having your cake and eating it: he took a 120,000-square-yard city-center park and effectively lifted it up into the air, sticking his futuristic Fukuoka Prefectural Hall underneath. The south-facing slope of the wedge-shaped building is covered in fourteen terraces of wild-looking vegetation that merges with a ground-floor park at its foot.

  Elsewhere in Asia, there are other record-breaking green architecture projects. Singapore boasts both the largest vertical garden (the 2,750-square-meter west-facing wall of the CDL Treehouse Condominium) and the stunning, thirty-story creeper-covered Oasia Hotel Downtown. Not that Asia is in any way unique in the green building world. In Milan, green architect Stefano Boeri built the Bosco Verticale (vertical forest), two residential towers planted with 730 trees, 5,000 shrubs, and 11,000 herbs. In fact, nature-inclusivity is in full swing in urban design and architecture worldwide, and more and more clever, ecologically inspired ideas are being developed to integrate nature into the city, on megalomanic as well as microscopic scales, and by building tycoons as well as tiny start-ups. In Manhattan, for example, the crowdfunded Lowline Lab is experimenting with creating underground green spaces under poor light conditions. The aim is to convert the abandoned, 200-yard-long Williamsburg Trolley Terminal underneath Delancey Street into dank cavernous spaces where mosses a
nd ferns may thrive in a subterranean park. And in Berlin, a local community is in the process of converting a behemoth of a Nazi-era concrete bunker into a “green mountain,” christened Hilldegarden.

  These new trends in design do not just give a boost to the architectural and designers’ guilds, there are many other benefits for the urban environment. For example, roofs are blatantly vacant in areas where competition for space is cutthroat. With cities growing and a rapidly dwindling availability of flat, low-lying land for nature and agriculture, why not bring these land-uses into the city, and onto those unused roofs? An added advantage of vegetation-clad constructions is that all that humid soil and foliage help a building stay cool. Air-conditioning costs go down and the urban heat island is mitigated as well. Moreover, the plants muffle noise and trap smog. In earthquake regions like Japan, a heavy rooftop park may even act as a counterweight and help to quake-proof the building. No wonder that in 2001, Tokyo passed an ordinance that says that new buildings need to devote 20 to 25 percent of their roof surface to greeneries. By 2015, this regulation had already yielded a total of 2.2 million square yards of green roofs. Similar regulations and incentives exist in cities all over the world.