To transhumanist thinkers, a posthuman is a hypothetical future being “whose basic capacities so radically exceed those of present humans as to be no longer unambiguously human by our current standards.”
The difference between the posthuman and other hypothetical sophisticated non-humans is that a posthuman was once a human, either in its lifetime or in the lifetimes of some or all of its direct ancestors. As such, a prerequisite for a posthuman is a Transhuman, the point at which the human being begins surpassing his or her own limitations, but is still recognizable as a human person or similar. In this sense, the transition between human and posthuman may be viewed as a continuum rather than an all-or-nothing event.
Posthumans could be a symbiosis of human and artificial intelligence, or uploaded consciousnesses, or the result of making many smaller but cumulatively profound technological augmentations to a biological human, i.e. a cyborg. Some examples of the latter are redesigning the human organism using advanced nanotechnology or radical enhancement using some combination of technologies such as genetic engineering, psychopharmacology, life extension therapies, neural interfaces, advanced information management tools, Cognitive enhancement drugs, wearable or implanted computers, and cognitive techniques.
“Posthuman” does not necessarily refer to a conjectured future where humans are extinct or otherwise absent from the Earth. As with other species who speciate from one another, both humans and posthumans could continue to exist. However, the apocalyptic scenario appears to be a viewpoint shared among a minority of transhumanists such as Marvin Minsky and Hans Moravec, who could be considered misanthropes, at least in regards to humanity in its current state. Alternatively, others such as Kevin Warwick argue for the likelihood that both humans and posthumans will continue to exist but the latter will predominate in society over the former because of their abilities.
Many science fiction authors, such as Greg Egan, Bruce Sterling, Greg Bear, Charles Stross and Ken MacLeod, have written works set in posthuman futures.
A variation on the posthuman theme is the notion of a “Posthuman God”; the idea that posthumans, being no longer confined to the parameters of “humanness,” might grow physically and mentally so powerful as to appear possibly god-like by human standards. This notion should not be interpreted as being related to the idea portrayed in some science fiction that a sufficiently advanced species may “ascend” to a higher plane of existence – rather, it merely means that some posthuman being may become so exceedingly intelligent and technologically sophisticated that its behavior would not possibly be comprehensible to modern humans, purely by reason of their limited intelligence and imagination. The difference here is that the latter stays within the bounds of the laws of the material universe, while the former exceeds them by going beyond it.