Editing Meaning of life (section)

===Origin and nature of biological life===
[[File:DNA Overview.png|thumb|left|upright=.5|[[DNA]] contains the genetic instructions for the development and functioning of all known [[life|organisms]].]]
The exact mechanisms of [[abiogenesis]] are unknown: notable hypotheses include the [[RNA world hypothesis]] (RNA-based replicators) and the [[iron-sulfur world hypothesis]] (metabolism without genetics). The process by which different lifeforms have developed throughout history via [[gene]]tic [[mutation]] and [[natural selection]] is explained by [[evolution]].<ref>[[Charles Darwin]] (1859). ''[[On the Origin of Species]]''.</ref> At the end of the 20th century, based upon insight gleaned from the [[gene-centered view of evolution]], biologists [[George C. Williams (biologist)|George C. Williams]], [[Richard Dawkins]], and [[David Haig (biologist)|David Haig]], among others, concluded that if there is a primary function to life, it is the replication of DNA and the survival of one's genes.<ref name="Dawkins selfish gene">{{Cite book |author=Richard Dawkins |author-link=Richard Dawkins |title=The Selfish Gene |publisher=Oxford University Press |date=1976 |isbn=978-0-19-857519-1|title-link=The Selfish Gene }}</ref><ref name="Dawkins river">{{Cite book |author=Richard Dawkins |author-link=Richard Dawkins |title=River out of Eden |publisher=Basic Books |location=New York |date=1995 |isbn=978-0-465-06990-3|title-link=River out of Eden }}</ref> Responding to an interview question from Richard Dawkins about "what it is all for", [[James Watson]] stated "I don't think we're ''for'' anything. We're just the products of evolution."<ref>{{Cite book|title = The God Delusion|url = https://archive.org/details/goddelusion00dawk_897|url-access = limited|last = Dawkins|first = Richard|publisher = Houghton Mifflin|date = 2006|isbn = 978-0-618-68000-9|pages = [https://archive.org/details/goddelusion00dawk_897/page/n109 99]–100}}</ref>

Though scientists have intensively studied [[organism|life on Earth]], defining [[life]] in unequivocal terms is still a challenge.<ref>{{cite web|url=http://www.astrobio.net/news/article226 |title=Complete Archive for Astrobiology Press Release, News Exclusive, News Briefs |work=Astrobiology Magazine |url-status=usurped |archive-url=https://web.archive.org/web/20081013130816/http://www.astrobio.net/news/article226 |archive-date=13 October 2008 }}</ref><ref>{{cite web|url=http://www.nbi.dk/~emmeche/cePubl/97e.defLife.v3f.html|title=Defining Life, Explaining Emergence|work=nbi.dk|access-date=2 November 2008|archive-url=https://web.archive.org/web/20120314095044/http://www.nbi.dk/~emmeche/cePubl/97e.defLife.v3f.html|archive-date=14 March 2012|url-status=dead}}</ref> Physically, one may say that life "feeds on [[negentropy|negative entropy]]"<ref name="worldtransformation.com">{{cite book |author=Griffith J. |year=2012 |chapter=What is the Meaning of Life? |title=The Book of Real Answers to Everything! |isbn=978-1-74129-007-3 |chapter-url=http://www.worldtransformation.com/what-is-the-meaning-of-life/ |access-date=19 November 2012}}</ref><ref>{{Cite book |last=Schrödinger |first=Erwin |title=What is Life? |publisher=Cambridge University Press |date=1944 |isbn=978-0-521-42708-1}}</ref><ref>{{Cite book |last=Margulis |first=Lynn |author-link=Lynn Margulis |author2=Sagan, Dorion |author2-link=Dorion Sagan |title=What is Life? |publisher=University of California Press |date=1995 |isbn=978-0-520-22021-8}}</ref> which refers to the process by which living entities decrease their internal [[entropy]] at the expense of some form of [[energy]] taken in from the environment.<ref>{{Cite book |last=Lovelock |first=James |title=Gaia – a New Look at Life on Earth |publisher=Oxford University Press |date=2000 |isbn=978-0-19-286218-1}}</ref><ref>{{Cite book |last=Avery |first=John |title=Information Theory and Evolution |publisher=World Scientific |date=2003 |isbn=978-981-238-399-0}}</ref><ref>{{cite web |url=https://www.youtube.com/watch?v=GcfLZSL7YGw&t=3s&ab_channel=PBSSpaceTime | archive-url=https://ghostarchive.org/varchive/youtube/20211030/GcfLZSL7YGw| archive-date=2021-10-30|author=[[Matt O'Dowd (astrophysicist)|O'Dowd, Matt, Ph.D.]]|title=The Physics of Life (ft. It's Okay to be Smart & PBS Eons!) Space Time |date=11 April 2018 |publisher=PBS Space Time}}{{cbignore}}</ref> Biologists generally agree that lifeforms are [[self-organization|self-organizing]] systems [[homeostasis|which regulate their internal environments as to maintain this organized state]], [[metabolism]] serves to provide energy, and [[reproduction]] causes life to continue over a span of multiple generations. Typically, organisms are responsive to stimuli and genetic information changes from generation to generation, resulting in adaptation through evolution; this optimizes the chances of survival for the individual organism and its descendants respectively.<ref>{{cite web|url=http://www2.una.edu/pdavis/BI%20101/Overview%20Fall%202004.htm |title=How to Define Life |access-date=17 October 2008 |last=Davison |first=Paul G. |publisher=The University of North Alabama |url-status=dead |archive-url=https://web.archive.org/web/20081101024755/http://www2.una.edu/pdavis/BI%20101/Overview%20Fall%202004.htm |archive-date=1 November 2008 }}</ref>

Non-cellular replicating agents, notably [[virus]]es, are generally not considered to be organisms because they are incapable of independent reproduction or metabolism. This classification is problematic, though, since some [[parasite]]s and [[endosymbiont]]s are also incapable of independent life. [[Astrobiology]] studies the possibility of different forms of life on other worlds, including replicating structures made from materials other than DNA.

All forms of life that are in existence today possess a self-replicating informational molecule (genome), and such an informational molecule is presumably intrinsic to life.  Thus the earliest forms of life also likely possessed a self-replicating informational molecule, possibly RNA<ref>{{cite journal |last1=Neveu |first1=M. |last2=Kim |first2=H.J. |last3=Benner |first3=S.A. |title=The "strong" RNA world hypothesis: fifty years old |journal=Astrobiology |volume=13 |issue=4 |pages=391–403 |date=April 2013 |pmid=23551238 |doi=10.1089/ast.2012.0868 |bibcode=2013AsBio..13..391N |url=}}</ref><ref>{{cite journal |last=Cech |first=T.R. |title=The RNA worlds in context |journal=Cold Spring Harb Perspect Biol |volume=4 |issue=7 |pages=a006742 |date=July 2012 |pmid=21441585 |pmc=3385955 |doi=10.1101/cshperspect.a006742 |url=}}</ref> or perhaps an informational molecule more primitive than RNA. The specific genomic sequences in all currently extant organisms contain order generating information  that promotes survival, [[reproduction]], and the ability to acquire resources necessary for reproduction. Sequences with such basic functions probably emerged early in the evolution of life. 

It has been proposed<ref name = Bernstein1983>Bernstein, Harris; Byerly, Henry C.; Hopf, Frederick A.; Michod, Richard A.; Vemulapalli, G. Krishna (June 1983). "The Darwinian Dynamic". The Quarterly Review of Biology. 58 (2): 185. doi:10.1086/413216. JSTOR 2828805. S2CID 83956410</ref> that both the evolution of macroscopic order in life (including its basic functions) and the evolution of order in particular physical systems obey a common fundamental principle that was termed the Darwinian dynamic.  This principal was formulated by considering, first, how macroscopic order is generated in a simple physical, non-biological system far from thermodynamic equilibrium, and then extending consideration to short RNA replicating molecules and then further to more complex forms of life.  It was concluded that the fundamental order-generating process was basically similar for both types of process.<ref name = Bernstein1983/><ref>Michod, Richard E. (2000). Darwinian Dynamics: Evolutionary Transitions in Fitness and Individuality. Princeton: Princeton University Press. ISBN 978-0-691-05011-9</ref>  Thus the idea that life likely emerged as a natural extension of simpler non- or pre-biological physical processes should logically be included in the concept "meaning of life".