Reuters/Gary Hershom

The archeologist and author Brenna Hassett explains how cities shaped our skeletons.

By 2030, humans will be a predominantly urban species, with 60 percent living in cities, according to a prediction from the United Nations Human Settlement Programme. To get to this point, evolution of both human species and our lifestyles has changed rapidly over time. A shift in habitat, the birth of modern cities, and our continuous urban experiment has left, in archeological terms, piles and piles of bones that tell us a lot about our problems, both past and present.

In her new book, Built on Bones: 15,000 Years of Urban Life and Death, the archeologist and author Brenna Hassett explains how cities have made us the way we are. CityLab spoke with Hassett to find out more about what our bones reveal about the metropolitan past and future.

In your book, you write about the idea that city living has seeped into our bones. Can you expand on that?

What I do is dig up dead people for answers on how humans live, so I’m very interested in bones. When I say that cities have gotten into our bones, I mean that we can see in the fossil record of human remains the evidence of changes that have physically happened to us over the last 15,000 years.

In the long, drawn-out process of running up to our modern cities, our bones have adapted. We’re in this funny push-pull where we come up with a wonderful, clever new invention like farming, and then it turns out to not be the greatest idea and so we fiddle with it a little bit and then it gets a little bit better. Cities are on that spectrum: we’re still in the process of adapting to them.

Does that mean our bones change along with how cities change over time?

In the book, I talk about different kinds of cities. I start by describing the changes that happened to our bodies, even before cities—for example, when we went from total paleo-hunter-gatherer lifestyle to farming. That, made our legs and muscles skinner since you’re not using them as much. Another thing to look at, in terms of city landscapes changing, is the movement of people. One of the consequences of a global-connected city is that when you move people, you move disease, and that definitely affects us physiologically.

Archeology students and workers clean the tomb of a priestess of the Moche culture excavated and found at San Jose de Moro Archaeological site in Trujillo, August 2, 2013. (Reuters/Mariana Bazo)

Is there any specific epidemic that illustrates something about the conditions of urban life?

The foundations of the medieval trade network allowed the plague, or Black Death, to run rampant. Cities don’t function without mechanisms for moving trade, goods, and people—but that connection also allows disease to move faster.

In addition to the plague, archaeologists, like looking at [bones of victims of] syphilis, because it’s really easy to see in the skeletons. But, we don’t know where exactly the disease came from, so we’re starting to bring in all this evidence to get a better idea. Similar to plague, syphilis was rampant at a time when cities were transforming. Once again, there’s a huge period of global connection driven by big cities. When big European cities pushed into North Africa and the New World during the colonial period, they brought back gold, trade, and other things to keep urban economies running—but on the back of it, they also brought back disease.

How did excavating bones help you understand inequality? It’s a major theme in your book.

Illnesses that signal nutritional deficiency—like rickets, which happens when you’ve got a lack of vitamin D, pop up in the very early stages of city formation. To archeologists, nutritional deficiencies are a sign of inequality. It makes a strong argument that from the beginning, cities have been engines for inequality—that cities are the places where we start to see people’s access to resources get limited.

You can actually bring all of that back to today: Where there’s a resurgence of rickets now, it’s a combination of health inequalities and cultural practices. Rickets and similar diseases are evidence of malnutrition, but more so, they reflect what happens to those on the lower end of the totem pole—and that’s a very city story.

Remains of Aztec children, recovered during the construction of a metro line in Mexico City, are displayed by the National Institute of Anthropology and History, August 17, 2010. (Reuters/Henry Romero)

In your book, you look at skulls to analyze patterns of violence in societies. What was the most interesting finding?

That’s a slightly weird one. People can be terrible, that’s kind of understood but it’s not clear if we’re more terrible in cities than we would be elsewhere. There’s a lot of argument about this, so what archeologists do is look at signs of violence. In the book I talk about fractured arms from self-defense, kicks to the head or arrows embedded in the shoulder. This violence doesn’t necessarily kill you—but it is sufficient enough to leave a shape on your bones. If you look at bones throughout the record, there is certainly evidence of violence before we settled into a semblance of city life. But as people started to get more organized in dense settlements, when people basically became urban, they had to find a way to deal with conflict—you cannot go around smashing your neighbor on their head everyday.

When people had to live closer together, they came up with social ways of settling conflict. What we might actually see then, is a decrease in the kind of general background violence as cities evolved. It’s an interesting theory that we still don’t have all the physical evidence for, but it’s not totally untrue—in our modern age, even though we have horrific violence when states have failed, the kind of day-to-day threat of it might actually be less than it was in the past. The jury is still out, but these are suggestions we are starting to see, from basically counting up how many skulls got bashed in the past.

What does all of this mean for the urban future?

Cities have given us a new ecological niche to survive in. If you were to look at another species of animal that wandered off from desert to rainforest, you would expect to see physical changes. Essentially, the changes in our bones reflect the same about cities—they reflect a new way of living.

Our crossed teeth that we need expensive dental work for us tell us about not having big, muscular jaws anymore; our diseases tell us about being in a world increasingly globally connected. Ultimately, cities make us this way. We built these cities, but they get a little of their own back.

Built on Bones: 15,000 Years of Urban Life and Death, came out February 23 and is available from Bloomsbury.

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