In the later part of the 19th century, new regulations on housing began to slowly ease the deadliness of the city. The crusading journalist and photographer Jacob Riis used the new technology of flash photography to capture images of the dark corners of the tenement world for an aghast public. His 1889 book How the Other Half Lives helped ignite a movement for tenement reform in New York. One of the first reforms, the Tenement House Act of 1901, required that city buildings provide exterior windows, ventilation, indoor toilets, and fire protections.
Some of the city’s neighborhoods didn’t survive this era of housing reform. For example, much of Five Points—an overcrowded Manhattan neighborhood that resembled others the anthropologist Wendy Orent classified as “disease factories”—was simply demolished. A sliver of the old neighborhood became what is now Chinatown. A similar area, the site of the old Collect Pond, became a small paved park fenced with chain link, surrounded by imposing government buildings: Superior Court, City Hall, and the clinics of the Department of Health of the City of New York, among others. Passersby would never suspect that a riotous neighborhood of any kind once existed there.
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Thanks to the housing revolution, even the most crowded cities can now be healthful places to live. In general, people who live in cities today live longer than those who live in rural areas. Only a few health burdens remain, like higher rates of obesity and more exposure to pollution.
And yet, though cities like New York may now appear to be largely washed clean of their past, the change they enjoyed has been partial and selective, passing over many of the poorer countries of the world. In India, due in part to poverty and in part to a lack of governance, housing regulations are as sparse and poorly enforced as in 19th-century New York. The densest streets of Dharavi, a slum of Mumbai, hold 1.4 million people in each square mile, more than seven times the concentration of humans packed into 19th-century Five Points.
And the process of urbanization that began in the industrial era is accelerating. Back then, urbanization was rapid, but it was still limited: Globally, more people lived outside cities than inside them. By 2030, experts estimate, that will change. The majority of humankind will live in large cities. Only a handful of these large metropolises will be healthful and well regulated; many will be more like Mumbai, and two billion of us will live in slums like Dharavi.
The growth of slums is one reason why the 2014 Ebola epidemic was so deadly and long-lasting. Before 2014, Ebola outbreaks had never occurred in towns with populations larger than a few hundred thousand. Just over a hundred thousand lived in Gulu, Uganda, in 2000, when Ebola emerged there; 400,000 people lived in Kikwit, the Democratic Republic of Congo town that experienced an Ebola outbreak in 1995. Since these locales were relatively small and remote, experts widely considered the virus, as the title of a 2011 scientific paper put it, a “minor public-health threat” in Africa.