b'
Violent crime rates in cities have declined significantly since the mid-1990s. We examine the reasons behind this drop, and the influence it has had on city life.
\\n\\nThen, concrete buildings are the foundation of the modern world. But they eat up a resource that\\u2019s becoming increasingly difficult to come by: sand.
\\n\\nFinally, for centuries, species have mutated to adapt to urban habitats. We investigate the wily ways that they continue to evolve in cities.
'