On March 28, 1838, Charles Darwin paid a visit to the London Zoo. At age 29, he was far from the scientific celebrity he would eventually become. It had only been two years since his return from his round-the-world voyage on the Beagle, and he was still methodically working his way through the heap of fossils and living specimens he had accumulated along the way. It would take more than two decades before he would present the world with his theory of evolution. In 1838, the theory was still in a primordial form in his mind. Darwin was struggling to find an explanation for how living things–humans included–got to be the way they are. And so, on that chilly spring day, Darwin went to the zoo and