The unique evolutionary story of the species-rich Central American land bridge is eloquently chronicled by Wallace (The Quetzal and the Macaw, 1992, etc.). Five million years ago, the Isthmus of Panama, the final puzzle-piece of what became known as Central America, poked its head above water, initiating the Great American Biotic Interchange. Species that had been specific to either North or South America commenced to cruise: dogs, cats, and deer went one way across the bridge, armadillos, porcupines, and opossums the other. Wallace's own first trip south, in 1971, was to Guatemala, where the unusual mixture of animals and plants aroused his curiosity. Why, he asked himself, was he running into turkeys and foxes in the deepest jungle? So he went back, time and again, to peruse the land bridge's complex physiography, a tangle of blue mountains and malarial lowlands, high plateaus and sierras, jaguar-infested savannas, lively volcanoes, and limestone caves. While delineating these landscapes, as well as the astounding fauna and flora, he twines the narrative with histories of Western adventurers (like Christopher Columbus, for whom a land bridge was the last thing he wanted to encounter, and who died convinced that Panama was southern China); the studies of naturalists such as the pirate William Dampier and Dominican priest Francisco Ximenez; tales of fossil-hunter Barnum Brown and paleontologist Stephen Jay Gould; and a portrait of the lives of today's inhabitants, described by one researcher thus: ""You can go from one little municipio to the next and find not just a completely different language, but a completely different way of looking at the world."" Wallace's wildlife gleanings are enviable: pheasant cuckoos, orange-bellied trogons, rainbow cichlids. A vibrant natural (and human) history of a biomassive throughway where large patches still remain unknown.