Human extinction refers to the possibility that the human species, Homo sapiens sapiens, is likely to someday die out completely, on Earth or in the entire universe. Most human extinction scenarios involve the eradication of humans from Earth which, being presently the only planet humans inhabit, would entail extinction of the entire species.

Humans consider the extinction of their own species to be one of the worst possible things that could happen, much worse than their own individual deaths. This is because, while individual death is almost universally considered inexorable, humans believe that their species will perpetuate indefinitely, or at least for an extremely long time. Humans also seek to attain immortality by having a permanent effect upon the world, through culture or science but most commonly through procreation. Eradication of the human species would represent an erasure of all those contributions.

Fear of human extinction is one motivation for the environmentalist movements of the 20th and 21st century.

Evidence for possible human extinction

About 99.9% of species that have ever existed on Earth are now extinct. Therefore, it is often suggested that all species have a finite lifespan. If this were the case, then human extinction would be inevitable. However, humans are unique in their adaptive and technological capabilities and it is safe to say that there is no precedent, positive or negative, from which one can draw inferences about the possibility of human extinction. However, the Earth will become uninhabitable in about 5 billion years, when the sun becomes a red giant. Another long-term threat is the eventual "heat death" of the universe predicted by the second law of thermodynamics.

A mass extinction event is underway on Earth, and humans are believed to be the culprit. Humans can create massive, often hazardous environmental changes including pollution and the destruction of animal habitats. Mostly, these extinctions are not intended by the human species but arise as unintended consequences from human activity, mostly of an economic sort. Extinctions tend to disrupt the ecosystem and may precipitate extinctions of more species. Therefore, it is possible that humans will unintentionally cause their own extinction through environmental destruction.

Case against human extinction

Humans have powerful adaptation abilities and have been able to populate the entire Earth. Technology allows the artificial creation of survivable climates and life support systems, allowing habitation of Antarctica and temporary habitation of underwater and outer space environments. Transport allows habitation of areas where adequate food does not exist naturally.

Future colonization of planets other than Earth is also a distinct possibility, and would allow the human species to survive even if the Earth were destroyed.

Human extinction scenarios

Scenarios for the eradication of the human species are offered in science, religion, and popular culture.

• Nuclear warfare,
• Biological warfare or a universal pandemic involving a genetic disease, fatal virus or prion, or antibiotic-resistant bacterium,
• Extinction by grey goo or following a war with artificially intelligent machines.
• Catastrophic environmental change, including the results of global warming,
• Famine resultant from overpopulation,
• The impact of an asteroid,
• Evolution into a superhuman lifeform, leaving no trace of the original human (speculative; see: pseudoextinction ),
• The creation of a world-swallowing black hole in a scientific experiment (highly speculative),
• Intervention by a God or gods (religious, not scientific) or
• Invasion of Earth by a militarily superior alien lifeform (mostly in popular culture, as there is no scientific evidence of this danger).