Introduction to evolution: Difference between revisions

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In [[biology]], '''evolution''' is the process of change in all forms of [[life]] over generations, and [[evolutionary biology]] is the study of how [[evolution]] occurs. Biological [[population]]s evolve through [[genetics|genetic]] changes that correspond to changes in the [[organism]]s' [[phenotypic trait|observable traits]]. Genetic changes include [[mutations]], which are caused by damage or replication errors in organisms' [[DNA]]. As the [[genetic variation]] of a population [[genetic drift|drifts]] randomly over generations, [[natural selection]] gradually leads traits to become more or less common based on the relative [[reproductive success]] of organisms with those traits.

The [[age of the Earth]] is about 4.5 billion0 years old.<ref name="USGS1997">{{cite web |url=http://pubs.usgs.gov/gip/geotime/age.html |title=Age of the Earth |date=July 9, 2007 |publisher=[[United States Geological Survey]] |access-date=2015-05-29}}</ref><ref>{{harvnb|Dalrymple|2001|pp=205–221}}</ref><ref>{{cite journal |last1=Manhesa |first1=Gérard |last2=Allègre |first2=Claude J. |author-link2=Claude Allègre |last3=Dupréa |first3=Bernard |last4=Hamelin |first4=Bruno |date=May 1980 |title=Lead isotope study of basic-ultrabasic layered complexes: Speculations about the age of the earth and primitive mantle characteristics |journal=[[Earth and Planetary Science Letters]] |volume=47 |issue=3 |pages=370–382 |bibcode=1980E&PSL..47..370M |doi=10.1016/0012-821X(80)90024-2}}</ref> The earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago.<ref name="Origin1">{{cite journal |last1=Schopf |first1=J. William |author-link1=J. William Schopf |last2=Kudryavtsev |first2=Anatoliy B. |last3=Czaja |first3=Andrew D. |last4=Tripathi |first4=Abhishek B. |date=October 5, 2007 |title=Evidence of Archean life: Stromatolites and microfossils |journal=[[Precambrian Research]] |volume=158 |pages=141–155 |issue=3–4 |doi=10.1016/j.precamres.2007.04.009|bibcode=2007PreR..158..141S }}</ref><ref name="Origin2">{{cite journal |last=Schopf |first=J. William |date=June 29, 2006 |title=Fossil evidence of Archaean life |journal=[[Philosophical Transactions of the Royal Society B]] |volume=361 |issue=1470 |pages=869–885 |doi=10.1098/rstb.2006.1834 |pmid=16754604 |pmc=1578735}}</ref><ref name="RavenJohnson2002">{{harvnb|Raven|Johnson|2002|p=68}}</ref> Evolution does not attempt to explain the origin of life (covered instead by [[abiogenesis]]), but it does explain how early lifeforms evolved into the complex ecosystem that we see today.<ref>{{cite web |url=http://evolution.berkeley.edu/evolibrary/misconceptions_faq.php#a1 |title=Misconceptions about evolution |website=Understanding Evolution |publisher=[[University of California, Berkeley]] |access-date=2015-09-26}}</ref> Based on the similarities between all present-day organisms, all life on [[Earth]] is assumed to have originated through [[common descent]] from a [[last universal ancestor]] from which all known [[species]] have diverged through the process of evolution.<ref>{{harvnb|Futuyma|2005a}}</ref>

All individuals have hereditary material in the form of [[gene]]s received from their parents, which they pass on to any offspring. Among offspring there are variations of genes due to the introduction of new genes via random changes called mutations or via reshuffling of existing genes during [[sexual reproduction]].<ref name="Gould">{{harvnb|Gould|2002|}}</ref><ref name="Gregory09">{{cite journal |last=Gregory |first=T. Ryan |author-link=T. Ryan Gregory |date=June 2009 |title=Understanding Natural Selection: Essential Concepts and Common Misconceptions |journal=Evolution: Education and Outreach |volume=2 |issue=2 |pages=156–175 |doi=10.1007/s12052-009-0128-1|doi-access=free }}</ref> The offspring differs from the parent in minor random ways. If those differences are helpful, the offspring is more likely to survive and reproduce. This means that more offspring in the next generation will have that helpful difference and individuals will not have equal chances of [[reproduction|reproductive]] success. In this way, traits that result in organisms being better [[adaptation|adapted]] to their living conditions become more common in descendant populations.<ref name="Gould" /><ref name="Gregory09" /> These differences accumulate resulting in changes within the population. This process is responsible for the many diverse life forms in the world.