This special volume covers not only North American animals, but the origin of all animals. Until the mid-19th century, most people believed all animals had always looked and acted exactly the same way from the moment they first appeared on Earth. When Charles Darwin published The Origin of Species in 1859, he turned that belief upside down, suggesting that animals change over time in response to changes in their environment. Learn why his theory of evolution changed science forever, and why the controversy continues today.