Evolution, 4th Edition

Some of the most avidly read books of the nineteenth century were the

tales that explorers recounted of their travels in exotic lands. They were the

Discover and National Geographic equivalents of their day. Some of them

were written by naturalists, such as Alexander von Humboldt, Alfred Russel

Wallace, and Charles Darwin, who climbed snow-clad mountains, traveled

unexplored rivers, and suffered tropical diseases. They told stories not only

of hardships and of encounters with indigenous peoples, but also of amaz-

ing animals and plants, utterly unlike any in Europe or North America. Some

of these organisms—African elephants, Australian kangaroos, South American

orchids—were already in zoos, botanical gardens, and museums, but these

were only a few of the many thousands of species that naturalists retrieved

from around the world. Every visitor to a zoo or garden might marvel at the

giraffes and be intrigued by giant cacti or Bornean pitcher plants, but the nat-

uralists went further: they asked why these creatures were found only in these

remote regions. Why should apes be in Africa but not South America, and

sloths in tropical America only? If European plants were found growing near

American seaports, having been accidentally transported across the Atlantic,

why had they not already occupied America? If those species could prosper

in what proved to be a suitable new region, why weren’t they already there?

Based both on their own travels and on specimens brought to Europe by

explorers, naturalists started to describe the faunal and floral differences among

regions of the world in the eighteenth century, and initiated the study of bioge-

ography, the geographic distributions of organisms. By placing this information

Hoofed mammals in the order Cetartiodactyla are among the many groups of

animals that do not extend east of Wallace's line, which separates a largely Asian

fauna from a characteristic Australian fauna. This bearded pig (Sus barbatus),

found in Borneo, is one of the easternmost hoofed mammals.

The Geography of Speciation

Patterns of evolution

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