Ed Yong in The Atlantic:
A young evolutionary biologist, Barrett had come to Nebraska’s Sand Hills with a grand plan. He would build large outdoor enclosures in areas with light or dark soil, and fill them with captured mice. Over time, he would see how these rodents adapted to the different landscapes—a deliberate, real-world test of natural selection, on a scale that biologists rarely attempt.
But first, he had to find the right spots: flat terrain with the right color soil, an abundance of mice, and a willing owner. The last of these was proving especially elusive, Barrett bemoaned. Local farmers weren’t keen on giving up valuable agricultural land to some random out-of-towner. After knocking on door after door, he had come up empty.