When the environment changes dramatically, animals from mollusks to crows can make big changes in their behavior that enable them to survive. For example, marmots and ground squirrels in California ...

Embryonic germ layers are the fundamental organizing principle in animal development. They provide the structural basis from which tissues and organs arise. During early embryogenesis, cells divide to ...

From butterflies to blue whales, corals and worms, Earth is home to an incredible diversity of animals. How all of these animals evolved from earlier, simpler ancestors is one of the most exciting ...