Charles Darwin was a 19th-century British naturalist. He is best known for his theory of evolution by natural selectionwhich transformed the way scientists perceive and interpret life on Earth.

Darwin’s theory, popularized in his book “On the Origin of Species,” states that environmental pressures determine which members of a species survive long enough to reproduce. Individuals of a species that are better adapted to their environment reproduce more often and pass their genes on to the next generation, thereby spreading certain physical and behavioral traits throughout the population. Eventually, these features – like the long necks of giraffes or the white fur of polar bears – come to dominate and shape the evolution of the species.