The urban monkeys in New Delhi are so bold they’ll steal the lunch right off your plate. If you’ve spent time in New York, you’ve probably seen squirrels try to do the same. Sydney’s white ibises got the nickname “bin chickens” for stealing trash and sandwiches. This brazen behavior isn’t normal for most species in the countryside, yet it shows up in urban wildlife, and not just in these cities. Studies show that animals living in urban environments around the world exhibit common sets of behaviors. At the same time, these urban animals are losing traits they would need in the wild. This process of urban animals’ behavior becoming more similar is known as “behavioral homogenization,” and it accompanies the loss of species diversity with urbanization. We study animals in urban settings to understand how humans can help wildlife thrive in an urbanizing world. In a new study, we explore the causes and the long-term consequences of these behavior changes for urban wildlife. What makes animals in cities similar? Cities, despite their local differences, share many of the same features worldwide: They are warmer than the surrounding countryside, noisy, polluted by light and, most importantly, dominated by people. New York’s squirrels, New Delhi’s monkeys, gulls in coastal cities of the U.K. and other urban wildlife have learned that people are a source of food. And because people typically don’t harm the animals, city-dwelling animals learn not to fear people. Cities drive evolution as well. Humans and the changes we’ve brought to cities have led to the survival of bolder animals, and those bolder animals pass on their traits to future generations. In genetics, scientists refer to this as the environment “selecting” for those traits. It’s not just sandwich-stealing that is more common among city wildlife; urban birds also sound more