Green iguana (Iguana iguana)

AMNH / Denis Finnin

From his very first stop in South America, Darwin was overwhelmed by the splendors of the Brazilian jungle. Among the marvels he saw there were large green iguanas peering down at him from tree branches. Extremely common in South America, the green iguana can grow up to two meters (6 feet) and can live 15 years. These animals are great climbers and spend most of their time in trees, eating leaves or sunning themselves.

"A Chaos of Delight"

In the year before his voyage, tantalizing pictures of lush South American jungles and the thrilling writing of Alexander von Humboldt had instilled in Darwin a longing to travel. But even the most vivid descriptions could not match his ecstasy at seeing the rain forest for himself:

"The delight one experiences in such times bewilders the mind,-if the eye attempts to follow the flight of a gaudy butter-fly, it is arrested by some strange tree or fruit; if watching an insect one forgets it in the stranger flower it is crawling over...The mind is a chaos of delight."