In placental mammals, larger species generally give birth to larger offspring (picture the size of cattle, elephants, and whales when they are born). This is not the case with bears. Brown bears are extremely small, averaging about 1 pound (.45 kg), at birth. This is tiny, especially compared to the mother bear which may weigh easily 400 pounds. Brown bear cubs are from 1/3 to 1/10 of that predicted for female mammals of comparable size.They are also blind and helpless at birth. Why would brown bears give birth to such small and vulnerable offspring? Like many natural phenomenon, no one knows for sure but biologists have some ideas.