But it took the genius of Charles Darwin and Alfred Russell Wallace, neither of whom ever visited Central America, to distill from the fossil record the true significance of the land bridge. What they saw was the demise of the South American megafauna and the rapid spread of North American mammals throughout the southern continent. If mammals pushed south, birds and fish, astonishingly diverse and abundant in South America, moved north. Generally the tropics acted like a great sieve, holding back most forms of life, allowing the penetration only of those capable of readily adapting to new possibilities. Such a digression is typical of a book that is as richly varied as the rain forest itself.
Anecdotes are often poignant and telling.
The reader learns, for example, that during the building of the Panama Railroad from 1850 to 1855, death was so common that the company financed its hospitals by shipping unclaimed corpses to medical schools in giant brine barrels. But the very density of the information is a flaw. Every chapter is a dizzying series of anecdotes, scientific names, uncommon animals, interspersed with references to distant geological upheavals and transformations, peppered with place names. This may overwhelm all but the most enthusiastic natural historian. Too often the anecdotes drawn from the author's many travels disrupt the narrative without necessarily illuminating the subject being discussed.