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A humanoid (//; 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).
Though no humanoid species has been discovered, the theory of convergent evolution speculates different species may evolve similar traits, and in the case of a humanoid these traits may include intelligence and bipedalism and other humanoid skeletal changes, as a result of similar evolutionary pressures. American psychologist Harry Jerison suggested the possibility of sapient dinosaurs. In 1978, he gave a presentation titled "Smart dinosaurs and comparative psychology", at a meeting of the American Psychological Association. According to his speech, dromiceiomimus supposedly could have evolved into a highly intelligent species like human beings. Simon Conway Morris counters this argument, arguing that convergence is a dominant force in evolution and that since the same environmental and physical constraints act on all life, there is an "optimum" body plan that life will inevitably evolve toward, with evolution bound to stumble upon intelligence, a trait of primates, crows, and dolphins, at some point.
In 1982, Dale Russell, curator of vertebrate fossils at the National Museum of Canada in Ottawa, conjectured a possible evolutionary path that might have been taken by the dinosaur Troodon had it not perished in the Cretaceous–Paleogene extinction event 66 million years ago, suggesting that it could have evolved into intelligent beings similar in body plan to humans, becoming a humanoid of dinosaur origin. Over geologic time, Russell noted that there had been a steady increase in the encephalization quotient or EQ (the relative brain weight when compared to other species with the same body weight) among the dinosaurs. Russell had discovered the first Troodontid skull, and noted that, while its EQ was low compared to humans, it was six times higher than that of other dinosaurs. If the trend in Troodon evolution had continued to the present, its brain case could by now measure 1,100 cm3; comparable to that of a human. Troodontids had semi-manipulative fingers, able to grasp and hold objects to a certain degree, and binocular vision.
Russell proposed that this "Dinosauroid", like most dinosaurs of the troodontid family, would have had large eyes and three fingers on each hand, one of which would have been partially opposed. As with most modern reptiles (and birds), he conceived of its genitalia as internal. Russell speculated that it would have required a navel, as a placenta aids the development of a large brain case. However, it would not have possessed mammary glands, and would have fed its young, as birds do, on regurgitated food. He speculated that its language would have sounded somewhat like bird song.
Russell's thought experiment has been met with criticism from other paleontologists since the 1980s, many of whom point out that his Dinosauroid is overly anthropomorphic. Gregory S. Paul (1988) and Thomas R. Holtz, Jr., consider it "suspiciously human" (Paul, 1988) and Darren Naish has argued that a large-brained, highly intelligent troodontid would retain a more standard theropod body plan, with a horizontal posture and long tail, and would probably manipulate objects with the snout and feet in the manner of a bird, rather than with human-like "hands".
A humanoid robot is a robot that is based on the general structure of a human, such as a robot that walks on two legs and has an upper torso, or a robot that has two arms, two legs and a head. A humanoid robot does not necessarily look convincingly like a real person, for example the ASIMO humanoid robot has a helmet instead of a face.
While there are many humanoid robots in fictional stories, some real humanoid robots have been developed since the 1990s, and some real human-looking android robots have been developed since 2002.
Similarly to robots, virtual avatars may also be called humanoid when resembling humans.
Deities are often imagined in human shape (also known as "anthropotheism"), sometimes as hybrids (especially the gods of Ancient Egyptian religion). A fragment by the Greek poet Xenophanes describes this tendency,
In animism in general, the spirits innate in certain objects (like the Greek nymphs) are typically depicted in human shape, e.g. spirits of trees (Dryads), of the woodlands (the hybrid fauns), of wells or waterways (Nereids, Necks), etc.
With regard to extraterrestrials in fiction, the term humanoid is most commonly used to refer to alien beings with a body plan that is generally like that of a human, including upright stance and bipedalism.
Many aliens in television and science fiction films are presented as humanoid. This is usually attributed to budget constraints, as human actors can more easily portray human-like aliens.
In much of science fiction, the reason for the abundance of humanoid aliens is not explained and requires suspension of disbelief. In some cases, however, explanations have been offered for this. In Star Trek, the abundance of humanoid aliens within the Star Trek universe is explained by advancing the story of a primordial humanoid civilization, the Ancient humanoids, who seeded the galaxy with genetically-engineered cells to guide the evolution of life on a multitude of worlds toward a humanoid form. In the television series Stargate SG-1, the Jaffa are explained as being an offshoot of humanity bred by the Goa'uld to suit their purposes, hence their almost-human appearance and physiology, while many other "alien" characters are actually the descendants of humans who were removed from Earth by the Goa'uld for use as slaves. Similarly, in its spin-off show Stargate Atlantis, the explanation offered for the humanoid appearance of the Wraith is that the Wraith evolved from a parasite which incorporated human DNA into its own genome after feeding on humans, giving the Wraith their present form.
In fantasy settings the term humanoid is used to refer to a human-like fantastical creature, such as a dwarf or an ogre. In some cases, such as older versions of the game Dungeons and Dragons, a distinction is made between demi-humans, which are relatively similar to humans, and humanoids, which exhibit larger differences from humans. Animals that are humanoid are also shown in fantasy. Humanoids are also used in some old horror movies, for example in Creature From the Black Lagoon, made in 1954 by Jack Arnold.