The book included evidence from the fossil record to discuss the processes of evolution and migration that had led to the geographical distribution of modern species. For example, he discussed how fossil evidence showed that tapirs had originated in the Northern Hemisphere, migrating between North America and Eurasia and then, much more recently, to South America after which the northern species became extinct, leaving the modern distribution of two isolated groups of tapir species in South America and Southeast Asia. Wallace was very aware of, and interested in, the mass extinction of megafauna in the late Pleistocene. In "The Geographical Distribution of Animals" (1876) he wrote, "We live in a zoologically impoverished world, from which all the hugest, and fiercest, and strangest forms have recently disappeared". He added that he believed the most likely cause for the rapid extinctions was glaciation, but by the time he wrote "World of Life" (1911) he had come to believe those extinctions were "due to man's agency".