Bears are thought to have evolved 40 million years ago from a
family of tree climbing carnivorous animals called miacids. These animals were
also the early ancestors of the dog family (Canidae) and the raccoon family (Procyonidae).
Today, the bear family, Ursidae, consists of 9 species. Until recently, giant pandas and red pandas were classified as members of the racoon family, but DNA studies in the 1980s established that pandas were more closely related to bears. Some scientists believe that the giant panda and the red panda should be placed in their own family, the Ailuropodidae.
Bears are found on all continents except Australia and Antarctica. Most bears are solitary and omnivorous which means that they feed on a variety of foods, including animal and plant matter. They tend to move slowly but are very capable of running fast if necessary.
Bears of colder climates tend to hibernate in winter, as there is not enough food to sustain their large bodies and if they didn't hibernate they would starve to death. Most species of bear undergo a period of delayed implantation during reproduction; the fertilized egg floats around in the uterus for several months before attaching itself to the wall of the uterus and beginning development. This enables the female to give birth to her cubs when climatic conditions and food availability are most suitable. If food availability is poor, the embryo is reabsorbed by the mother's body.
Bears have an aggressive reputation, but in most cases this is undeserved. Find out more about the bears of the world.