Brenna Hassett is a bioarchaeologist. Her book Built on Bones: 15,000 Years of Urban Life and Death looks at the millennia-long story of how our urban lives have affected our very bones. She is also 1/4 of the TrowelBlazers, an advocacy group that celebrates women’s contributions to the digging sciences: archaeology, geology, and palaeontology. 

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1. Are we still evolving?

Any species that has the capacity to change and grow, to adapt to new environments and circumstances – that’s a species with a potential for evolution.  The changes our species has made to our ecological niche over the last few hundred thousand years have been astonishing, extending our range from Africa to the Arctic and going from endurance hunting to ordering online. Of course this feeds back into our biological development – weedier legs as we move around less and rotten, ill-fitting teeth as we change our diet. To see so much change in just the last 15,000 years suggests that what we think of as ‘us’ is actually a pretty fluid concept – and we haven’t opted out of the evolutionary race for survival just yet.

2. Are cities killing us?

Yes. More specifically, they are killing the most vulnerable among us. One of the major problems with getting so many humans together in one place is that most of the systems we have come up with for organizing that kind of party tend to have someone at the top who does super well, and a bunch of folk at the bottom who don’t. The inequality that lies at the heart of most of the real urban killers – density, disease and dirt – has been with us since we invented cities. We can trace these patterns back thousands of years, looking at evidence of malnutrition, epidemic diseases, and the filthy living conditions in archaeological cities. Cities are full of people who have different accesses to resources, which in the present means babies born to the poorest 20% of the world’s urban dwellers are nearly twice as likely to die in childhood than the babies of the urban top 20%; inequality is still a major predictor of urban life chances. 

3. Why did we keep living in cities if it was so bad for our health?

They are one of the stranger inventions we have come up, these dangerous, unequal cities; however, in the 21^st century the view out the window is urban for more than half of us. From the very beginning, the changes that led us to this moment threw up warning signs, but we appeared to have (quite literally) ploughed on.  Switching over to agriculture seems to have been pretty hard on us, and we have evidence of distressed childhoods stretching back ten millennia locked in bones and teeth.  Cramming people all together in a city has let in a host of diseases and some of our less savoury traits (like war, slavery and the rest) wreak havoc. But sometimes looking at the forest can tell you more than any one tree: all those urban innovations that leave their scars on our skeletons actually produce more skeletons. Human populations expand rapidly with the ‘Neolithic’ and ‘Urban’ revolutions. If evolution is a numbers game, cities are our way to win.

4. Is there any reason to be hopeful for our species’ future?

Change is part of any species’ story, and one of the startling things about humans is that we are very, very good at adapting to change. We use the rather particular tool of ‘culture’ to transmit our knowledge, our values, and our survival skills.  When we build up our numbers to the point that resources are scarce and tempers boil, we invent new ways of organizing ourselves politically so we don’t end up just trying to kill each other all the time. These might not always work, and sometimes cause more problems than they solve (you could for instance ask what the prisoner trussed up on the altar thinks about how functional human sacrifice is). But cities are also where we can build up spare capacity that frees us from the grind of daily survival. Cities give us the specialists who solve the problems we create: hospitals for our diseases, public health institutes for our dirt. That is what cities are for in the end – a cultural adaptation that allows us to expand our numbers and, more hopefully, the possibilities for our species’ future.