In biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

 and ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

, extinction is the end of an organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

 or of a group of organisms (taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...

), normally a species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover
Functional extinction
Functional extinction is the extinction of a species or other taxon such that:#it disappears from the fossil record, or historic reports of its existence cease;#the reduced population no longer plays a significant role in ecosystem function; or...

 may have been lost before this point. Because a species' potential range
Range (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...

 may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa
Lazarus taxon
In paleontology, a Lazarus taxon is a taxon that disappears from one or more periods of the fossil record, only to appear again later. The term refers to the account in the Gospel of John, in which Jesus raised Lazarus from the dead...

, where a species presumed extinct abruptly "re-appears" (typically in the fossil record
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

) after a period of apparent absence.

Through evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

, new species arise through the process of speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...

—where new varieties of organisms arise and thrive when they are able to find and exploit an ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...

—and species become extinct when they are no longer able to survive in changing conditions or against superior competition.

The Dodo never had a chance. He seems to have been invented for the sole purpose of becoming extinct and that was all he was good for. -- id.

Becoming extinct has its compensations. It's a good deal like beating the game. I would go so far as to say that becoming extinct is the perfect answer to everything and I defy anybody to think of a better. Other solutions are mere palliatives, just a bunch of loose ends, leaving the central problem untouched. --id.

"EXTINCTION: The end of the line for creatures that cannot or will not adapt to an increasingly hostile environment, which is why the future belongs to cockroaches and MBAs." -- Rick Bayan, The Cynic's Dictionary

Since after extinction no one will be present to take responsibility, we have to take full responsibility now. -- Jonathan Schell|Jonathan Schell, The Fate of the Earth, 1982, ISBN 0-39452-559-0

The beauty and genius of a work of art may be reconceived, though its first material expression be destroyed; a vanished harmony may yet again inspire the composer; but when the last individual of a race of living beings breathes no more, another heaven and another earth must pass before such a one can be again. -- William Beebe, The Bird, 1906

Extinction is forever. -- popular slogan. Category:Themes