Life
From Wikinfo
Alternate meanings: Conway's Game of Life, Hasbro's Game of Life, personal life, Life magazine
Life is an energetic forcefulness toward survival. It is observed to be a dynamic, changing biological condition. Life flourishes in systems where its many forms interact with each other. If life were trying to destroy itself, it would have done so long ago, but it survives, reproduces, and survives. In doing so, it creates conditions wherein more complex life can live. Something is usually defined to be alive if it matches all of the following conditions, at least once during its existence its life:
- Growth
- Metabolism, the uptake of food, conversion of food into energy, and disposal of waste products
- Motion, either moving itself, or having internal motion
- Reproduction, the ability to create more-or-less exact copies of itself
- Stimulus response, the ability to measure properties of its surrounding environment, and act on certain conditions.
Controversially, according to this definition,
Lynn Margulis defined life as an autopoietic (self-producing), water based, lipid-protein bound, carbon metabolic, nucleic acid replicated, protein readout system. Other definitions are
- "a system of inferior negative feedbacks subordinated to a superior positive feedback" (J. theor Biol. 2001);
- "functional organization for sustaining self and kind, involving active use of energy and information replication (respectively)" (Human Knowledge: Foundations and Limits, which classifies about 25 categories of replicating or self-sustaining phenomena).
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 evolution, assuming the variations in the offspring allow for differential survivability. The study of this form of inheritability is called genetics, and in all known life forms with the exception of prions the genetic material is primarily DNA or the related molecule RNA.
Note that some individual organisms are incapable of reproduction and yet are alive, for example, mules and ants.
Currently (2003), the Earth is the only planet in the Universe known by humans to support life. The question of whether life exists 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 bacterial life on Mars.
All life on Earth is based on the chemistry of carbon compounds. Some assert that this must be the case for all possible forms of life throughout the Universe; others describe this position as 'carbon chauvinism'.
Most successful animal of the earth in terms of biomass: Antarctic krill, Euphausia superba, its biomass is probably over 500 million tonnes.
Lifespan is the length of life of an individual of a species.
Death is the termination of life of an individual of a species.
Life insurances, including pensions and life annuities, provide payments depending on life or death of a particular person. Accordingly, documents that may be required for payment are:
- a life certificate stating that a person was alive at the date of issue;
- a death certificate stating that a person died on a particular date.
See also: Meaning of life, Vitalism, Materialism, Artificial life, Value of life, Afterlife
References
- Adapted from the Wikipedia article, "Life" http://www.wikipedia.org/wiki/Life August 16, 2003
