The year was 1848. a young British naturalist named Henry Walter Bates had gone to the Amazon with fellow countryman Alfred Russel Wallace to look for evidence of the origin of species. Over the course of his 11-year stay, he noticed that local relatives of a European butterfly known as the cabbage white—the pierids—were bedecked in the showy reds and yellows of rain forest butterflies called heliconids. Observing that the heliconids seemed to possess toxins that made them unpalatable to predators, Bates reasoned that by mimicking the toxic heliconids’ warning colors, the harmless pierids were escaping predation. When Bates returned to England in 1859, the year that Charles Darwin published On the Origin of Species, his discovery of these “mockers,” as he called them, became the first independent evidence to corroborate Darwin’s theory of evolution by natural selection—which holds that organisms best able to meet the challenges in their environment survive to produce the most offspring, so that their traits become increasingly common through the generations.