A humanoid (/ˈhjuːmənɔɪd/; from English human and -oid "resembling") is something that has an appearance resembling a human being. The earliest recorded use of the term, in 1870, referred to indigenous peoples in areas colonised by Europeans. By the twentieth century, the term came to describe fossils which were morphologically similar, but not identical, to those of the human skeleton. Although this usage was common in the sciences for much of the twentieth 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 anterior forelimb-appendages (thumbs), visible spectrum-binocular vision (having two eyes), or biomechanic digitigrade-bipedalism (the ability to walk on heels in an upright position).

In theoretical convergent evolution

Although there are no known humanoid species outside the genus Homo, the theory of convergent evolution speculates that different species might evolve similar traits, and in the case of a humanoid these traits might include intelligence and bipedalism and additional humanoid skeletal changes, as a result of similar evolutionary pressures. American psychologist and Dinosaur intelligence theorist Harry Jerison suggested the possibility of sapient dinosaurs. In a 1978 presentation at the American Psychological Association, he speculated that dromiceiomimus could have evolved into a highly intelligent species like human beings. In his book, Wonderful Life, Stephen Jay Gould argues that if the tape of life were re-wound and played back, life would have taken a quite different course. Simon Conway Morris counters this argument, arguing that convergence is a dominant force in evolution and that after the same environmental and physical constraints act on all life, there's 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 a few point.

A model of the hypothetical Dinosauroid, Dinosaur Museum, Dorchester

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, fitting 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 additional 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 additional 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. Notwithstanding it wouldn't 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 additional palaeontologists after the 1980s, a large number of 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".

In robotics

A humanoid robot is a robot that's 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 doesn't necessarily look convincingly like a real person, for example the ASIMO humanoid robot has a helmet instead of a face.

An android (male) or gynoid (female) is a humanoid robot designed to look as much like a real person as possible, although these words are frequently perceived to be synonymous with humanoid.

While there are a large number of humanoid robots in fictional stories, a few real humanoid robots have been developed after the 1990s, and a few real human-looking android robots have been developed after 2002.

Similarly to robots, virtual avatars might additionally be called humanoid when resembling humans.

In mythology

Deities are often imagined in human shape (also known as "anthropotheism"), at times as hybrids (especially the gods of Ancient Egyptian religion). A fragment by the Greek poet Xenophanes describes this tendency,

...Men make gods in their own image; those of the Ethiopians are black and narrow-nosed, those of the Thracians have blue eyes and red hair.

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.

In science fiction

With regard to extraterrestrials in fiction, the term humanoid is most commonly used to refer to alien beings with a body plan that's 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.

Fictional extraterrestrials

In much of science fiction, the reason for the abundance of humanoid aliens isn't explained and requires suspension of disbelief. In a few 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 storey 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 hundred-thousand year offshoot of humanity bred by the Goa'uld to suit their purposes, hence their almost-human appearance and physiology, while a large number of additional "alien" characters are actually the descendants of human-slaves who were removed from Earth by the Goa'uld. Here on Earth, any species segregated from the main genus for at least 10k years might be considered a new sub-species; any humans isolated on multiple planets after 100k+ years of adaptations would most certainly seem "alien" to Earthlings. 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 ufology

In the field of ufology, humanoid refers to any of the claimed extraterrestrials which abduct human victims, such as the Greys, the Reptilians, Nordics, and Martians.

In fantasy

In fantasy settings the term humanoid is used to refer to a human-like fantastical creature, such as a dwarf, elf, gnome, halfling, goblin, troll, orc or an ogre, and Bigfoot . In a few 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 additionally shown in fantasy. Humanoids are additionally used in a few old horror movies, for example in Creature From the Black Lagoon, made in 1954 by Jack Arnold.