First, no one is sure why we, or any other animal, dream. During the past century, however, scientists have made significant progress in understanding the factors that influence sleep and dreaming.

Throughout the past 500 million years, our planet has experienced a total of five mass extinctions. One of these—the Permo-Triassic mass extinction event—led to the demise of roughly 90% of Earth's ...

It would seem that communication among animals is easy. For instance, a bark may be used to warn of danger, and a call may be used to bring the group together. The communication appears to be easy and ...