Masked titi photo: Andy Young

Though not as obvious as Earth’s impressive array of species and ecosystems, genes—the basic units of heredity—are an equally important aspect of biodiversity. Many plant and some animal species have as many as 400,000 genes—giving rise to enormous possibilities for genetic variation.

For a vivid portrait of genetic diversity, just look around. It’s evident in the different colors and shapes of apples in the supermarket, in the different eye and hair colors of humans, and in the different songs and behavior patterns of birds, to name a few examples.