A lone naked human is at a physical disadvantage to other comparable apex predators in areas such as speed, bone density, weight, and physical strength. Humans also lack innate weaponry such as claws. Without crafted weapons, society, or cleverness, a lone human can easily be defeated by fit predatory animals, such as wild dogs, big cats and bears (see Man-eater). However, humans are not solitary creatures; they are social animals with highly developed social behaviors. Early humans, such as Homo erectus, have been using stone tools and weapons for well over a million years. Anatomically modern humans have been apex predators since they first evolved, and many species of carnivorous megafauna actively avoid interacting with humans; the primary environmental competitor for a human is other humans. The one subspecies of carnivorous megafauna that does interact frequently with humans in predatory roles is the domestic dog, but usually as a partner in predation especially if they hunt together. Cannibalism has occurred in various places, among various cultures, and for various reasons. At least a few people, such as the Donner party, are said to have resorted to it in desperation.