Among the many primate species, the great apes are unique and share several important traits. This taxonomic family includes gorillas, chimpanzees, bonobos, orangutans and, according to some experts, humans. Great apes are not only the largest primates, but also the most cognitively advanced. With the exception of humans, great apes typically move around on all four limbs (but they can walk on two feet for short distances). Their arms are longer than their legs and, like us, they have opposable thumbs—essential to manual dexterity. Great apes all have similar gestation periods, and females care for their offspring for many years after their birth. Apart from us humans, however, the other great ape species are under constant threat and struggling for survival.