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'''Life''' may refer to:
]
'''Life''' has no simple ]. Apart from countless ] definitions and explanations, something is usually defined to be alive if it matches the following conditions, at least once during its existence:


* ]
*''Growth''
* ]
*], the uptake of food, conversion of food into energy, and disposal of waste products
* philosophical view of "life" : ]
*''Motion'', either moving itself, or having internal motion
* ]
*], the ability to create more-or-less exact copies of itself
⚫ * ].
*''Stimulus response'', the ability to measure properties of its surrounding ], and act on certain conditions.

As are all other known definitions of life, this one is inadequate. According to this definition,
*] is alive
*] are not

] has provided what may be the most satisfying definition of life. She defined life as an autopoietic (self-directed), ] based, ]-] bound, ] metabolic, ] replicated, protein readout ].

Perhaps a more useful characteristic upon which to base a definition of life is that of descent with modification; the ability of a life form to produce offspring that are like it but that also have the possibility of random variations. This characteristic alone is sufficient to allow ], assuming the variations in the offspring allow for differential survivability. The study of this form of heritability is called ], and in all known life forms with the exception of ]s the genetic material is primarily ] or the related molecule ]. Another exception might be the ] code of certain forms of ] and programs created through ], but whether ] programs can be alive even by this definition is still a matter of some contention.

Note that many individual organisms are incapable of reproduction and yet are still generally considered to be "alive;" see ]s and ]s for examples. However, these exceptions can be accounted for by applying the definition of life on the level of entire ] or of individual ]s (for example, see ] for one way that non-reproducing individuals can still enhance the spread of their ] and the survival of their species).

Currently (]), the ] is the only planet in the ] known to support life. The question of whether life exist elsewhere in the Universe remains an open question. There have been a number of false alarms of life elsewhere in the Universe, but none of these apparent discoveries have so far survived scientific scrutiny.

Currently the closest that scientists have gotten to finding extraterrestrial life is fossil evidence of possible ]l life on ].

All life on Earth is based on the ] of ] compounds. Some assert that this must be the case for all possible forms of life throughout the Universe; others describe this position as ']'.

See also: ]

----
⚫ '''Life''' also means ] and ].

Revision as of 02:13, 29 December 2002

Life may refer to: