Cities cover just 3% of the planet's land surface, but are already home to more than half of its people. That means cities are bringing people into ever greater contact, where collectively they act as a giant physical, biological and cultural force. Transport links and communication between cities, from superhighways to express trains and planes, allow businesses to operate planet-wide, shrinking the human world and making the global local.

The great homogenisation of the Anthropocene includes human culture and lifestyle as much as any effect on the natural ecosystem. And cities are the biggest expression of that. They truly are universal. I feel at home in cities around the world precisely because they essentially provide the same experience. Some are more violent, or more sleepy, or more wealthy, but the urban environment is at its heart the same. There is not the vast diversity of landscape and experience that exists across the natural world.

The sheer concentration of people attracted by the urban lifestyle means that cosmopolitan cities like New York are host to people speaking more than 800 different languages – thought to be the highest language density in the world. In London, less than half of the population is made of white Britons – down from 58% a decade ago. Meanwhile, languages around the world are declining at a faster rate than ever – one of the 7,000 global tongues dies every two weeks.

It is having an effect not just culturally, but biologically: urban melting pots are genetically altering humans. The spread of genetic diversity can be traced back to the invention of the bicycle, according to geneticist Steve Jones, which encouraged the intermarriage of people between villages and towns. But the urbanisation occurring now is generating unprecedented mixing. As a result, humans are now more genetically similar than at any time in the last 100,000 years, Jones says.

The genetic and cultural melange does a lot to erode the barriers between races, as well as leading to novel works of art, science and music that draw on many perspectives. And the tight concentration of people in a city also leads to other tolerances and practices, many of which are less common in other human habitats (like the village) or in other species. For example, people in a metropolis are generally freer to practice different religions or none, to be openly gay, for women to work and to voluntarily limit their family size despite – or indeed because of – access to greater resources.

Virtual revolution

Now that the technology exists for individuals to communicate instantly with companies, government departments, to broadcast to millions or to specific groups over the internet, the city has gained an entirely new dimension. This “virtual city” of communities formed online, using social networks like Twitter or Facebook, is incredibly powerful and not necessarily limited to the geographical contours of the real city. Like-minded individuals can find each other easily, gathering in online forums or through hashtags and comment streams in the same way as special interest clubs and cafe movements coalesce in the real city. Virtual applications make it easier to sift through a crowd – the Grindr app, for example, allows gay people to find other users of the app in a public setting. Online clubs – like the shopping network Groupon – are attempting to personalise trade exchanges and perhaps develop a proxy for the relationship people might have with a neighbourhood store.

Those petitioning for social or political change can hold governments and companies accountable in a manner never possible before. Instead of ploughing through books of corporate ledgers in libraries, vast amounts of data are now published online and can be searched and filtered in minutes with algorithms, allowing journalists and other groups to discover corruption, tax evasion or other information of public interest. Such information can be self-published in seconds, where it is available for billions to see. In a few seconds, I can compare hospital cancer survival rates in my area or nationally, I can look up how much profit popular stores shift to offshore accounts to avoid taxation, or read hundreds of reviews of a product I’m thinking of buying.

The virtual and real cities are closely enmeshed. Information gathering and community building can take place more easily online than in the vast cities of the Anthropocene, where members of a group may live far from each other or be unable to meet easily for momentum-building. But the discussions and real-world changes these online gatherings initiate move easily to government chambers, mainstream media outlets in television, radio and press, or onto the streets. The Arab revolutions across Northern Africa and the Middle East since 2010 were coordinated via the virtual city of Twitter, Facebook, SMS messaging and other apps, but they took place on the streets and squares of the real cities, uniting flesh-and-blood individuals who had united online using computers and smartphones. Starbucks was compelled by a Twitter campaign to pay billions of pounds of tax to the UK government after its perfectly legal offshore tax evasion was revealed in 2012.

So the virtual city is as global as it is local. I can get hourly updates on air-pollution levels in my neighbourhood or buy a new battery for my phone from Korea. People from across the world can gather online to share ideas, pressure for change, innovate, spread their artistic talents or make friends. The virtual city provides a way of shrinking and filtering the real megacity, saving time and energy on real journeys across complicated spaces, of accessing multiple conversations with relative anonymity, and of individually helping steer humanity through collaborative creativity and problem solving. It enhances but doesn’t replace the real city with its face-to-face social cues, physical exchanges and wealth of information humans use to make judgements about trustworthiness and other value-laden decisions.

The virtual city does have a more problematic side, however. Never has there been so much information about so much of our lives in such an accessible form. In the course of a day, the average person in a Western city is said to be exposed to as much data as someone in the 15th century would encounter in their entire life. The digital birth of a baby now precedes the analogue version by an average of 3 months, as parents post sonogram images on Facebook and register their infant’s domain name before the child is even born. Governments, groups, individuals and corporations can access data about us and use it for their own purposes.

This erosion of individual privacy can be benign or malevolent, but it is already a part of life in the Anthropocene. Customer data collected by the US supermarket Target allows it to identify with a high degree of accuracy which shoppers have recently conceived and when their due date is. The store uses this information to target such women for advertising of its pregnancy and baby products in a timely fashion, even if she has not yet told anyone else. Sinister? Maybe. What about police officers identifying householders as marijuana growers by analysing energy use data? Or neighbours targeting individuals for cyber or physical bullying because of information they discover online? We’re all generating data, every time we make an ATM transactions or log onto a website. In the Anthropocene, we will have to decide who owns our data and whether it can be shared.

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