Alfred Russel Wallace from the frontispiece of Darwinism 1889
The current issue of Nature (here) carries an appreciation of Alfred Russel Wallace, who independently of Darwin hit upon the principle of natural selection. He had a firm grasp of the species concept based on his experiences in Amazonia. In 1852 he reported on the distribution of Neotropical primates writing, "I soon found that the Amazon, the Rio Negro and the Madeira formed the limits beyond which species never passed" (On the monkeys of the Amazon Proc Zool Soc Lond 1852; 20: 107-110).
Humming-bird fertilizing Maregravia nepenthoides
from Darwinism 1889
Wallace was based on Barra at the confluence of the Amazon and the Rio Preto. During the subsequent rubber boom it was transformed to the prosperous city of Manaus with a world class opera house. It is now home to the prestigious National Institute of Amazonian Research (INPA). Wallace's expedition, however, ended with the loss of many of his specimens in a fire on the ship that was to have carried him back to England.
The man who knew islands
Next Wallace went to Indonesia. His work there is recounted in The Malay Archipelago (1869), as reviewed in a companion article in Nature by Richard Quammen. Wallace is regarded as the father of biogeography. Quammen devoted a long chapter to him in the prize winning book Song of the Dodo (reviewed here). Among his legacy is the concept known as the Wallace Line, a water barrier that separates the Southeast Asian and Australasian flora and fauna. If you are planning a trip to Bali remember to include the Gili Isles and you will cross the Wallace Line as you go.
To finance his travels, Wallace collected many specimens of the same species. As Quammen writes, "one effect of this redundant, commercial collecting was that he saw intraspecific variation laid out before him." This led him to the principle of natural selection, which Darwin was slow to gestate.