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Field Guide to Species

Ernst Mayr, a German-born biologist known for his insights into evolution, will celebrate his 93rd birthday on Saturday. In the early part of his career, Mayr studied birds in New Guinea. His 1941 book, List of New Guinea Birds, describes how to distinguish between closely related species and describes how variations arise within species.

A year later, Mayr published a work that is still considered a bible for evolutionary biologists: Systematics and the Origin of Species. In the book, Mayr details the process behind speciation, arguing that new species arise when a few organisms become geographically isolated and, after many generations, change so much that they can no longer breed with the original group. In recent years, Mayr, a professor emeritus at Harvard University, has criticized a cottage industry of what he calls "armchair taxonomists"--scientists who attempt to classify species without studying them in the field.