A humanoid (/ˈhjuːmənɔɪd/; from English human and -oid "resembling") is something that has an appearance resembling a human being. The term first appeared in 1912 to refer to fossils which were morphologically similar to, but not identical with, those of the human skeleton. Although this usage was common in the sciences for much of the 20th century, it is now considered rare. More generally, the term can refer to anything with uniquely human characteristics and/or adaptations, such as possessing opposable appendage (thumbs), binocular vision (having two eyes), or biomechanic bipedalism (the ability to walk in an upright position). Humanoids can arise naturally through natural selection or can be created through genetic engineering and to a degree selective breeding. A humanoid usually has two arms, two legs, and one head, or a human-like torso, and a head. Most humanoids can speak human langauge and usually have well-developed societies.