past geographic distribution of animals within each geographic region. These factors included the effects of the appearance and disappearance of land bridges (such as the one currently connecting North America and South America) and the effects of periods of increased glaciation. He provided maps showing factors, such as elevation of mountains, depths of oceans, and the character of regional vegetation, that affected the distribution of animals. He summarised all the known families and genera of the higher animals and listed their known geographic distributions. The text was organised so that it would be easy for a traveller to learn what animals could be found in a particular location. The resulting two-volume work, The Geographical Distribution of Animals, was published in 1876 and served as the definitive text on zoogeography for the next 80 years. 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". In 1880, Wallace published the book Island Life as a sequel to The Geographical Distribution of Animals. It surveyed the distribution of both animal and plant species on islands. Wallace classified islands into oceanic and two types of continental islands. Oceanic islands, in his view, such as the Galapagos and Hawaiian Islands (then called Sandwich Islands) formed in mid-ocean and never part of any large continent. Such islands were characterised by a complete lack of terrestrial mammals and amphibians, and their inhabitants (except migratory birds and species introduced by humans) were typically the result of accidental colonisation and subsequent evolution. Continental islands, in