Introduction to evolution: Difference between revisions

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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.

The modern understanding of evolution began with the 1859 publication of [[Charles Darwin]]'s ''[[On the Origin of Species]]''. In addition, [[Gregor Mendel]]'s work with plants, between 1856 and 1863, helped to explain the hereditary patterns of [[genetics]].<ref name="gegme">{{cite web |url=http://www.accessexcellence.org/RC/AB/BC/Gregor_Mendel.php |title=Gregor Mendel (1822–1884) |last=Rhee |first=Seung Yon |website=Access Excellence |publisher=National Health Museum |___location=Atlanta, GA |access-date=2015-01-07 |url-status=dead |archive-url=https://web.archive.org/web/20141227004122/http://www.accessexcellence.org/RC/AB/BC/Gregor_Mendel.php |archive-date=2014-12-27}}</ref> Fossil discoveries in [[palaeontology]], advances in [[population genetics]] and a global network of scientific research have provided further details into the mechanisms of evolution. Scientists now have a good understanding of the origin of new species ([[speciation]]) and have observed the speciation process in the laboratory and in the wild. Evolution is the principal [[scientific theory]] that [[biologist]]s use to understand life and is used in many disciplines, including [[medicine]], [[psychology]], [[conservation biology]], [[anthropology]], [[Forensic science|forensics]], [[agriculture]] and other [[Sociocultural evolution|social-cultural]] applications.

== Simple overview ==

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{{main|Natural selection}}

In the 19th century, [[natural history]] collections and museums were popular. The European expansion and naval expeditions employed [[Natural history|naturalists]], while [[curator]]s of grand museums showcased preserved and live specimens of the varieties of life. Charles Darwin was an English graduate, educated and trained in the disciplines of natural history. Such natural historians would collect, catalogue, describe and study the vast collections of specimens stored and managed by curators at these museums. Darwin served as a ship's naturalist on board [[HMS Beagle|HMS ''Beagle'']], assigned to a five-year research expedition around the world. During his voyage, he observed and collected an abundance of organisms, being very interested in the diverse forms of life along the coasts of South America and the neighbouring [[Galápagos Islands]].<ref>{{harvnb|Farber|2000|p=136}}</ref><ref>{{harvnb|Darwin|2005}}</ref>

[[File:Haeckel Orchidae.jpg|thumb|left|upright|Darwin noted that [[Orchidaceae|orchids]] have complex [[adaptation]]s to ensure pollination, all derived from basic floral parts.]]

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== Genetic drift ==

{{Further|Genetic drift}}

Genetic drift is a cause of allelic frequency change within populations of a species. [[Allele]]s are different variations of specific genes. They determine things like [[Human hair color|hair colour]], [[Human skin color|skin tone]], [[eye colour]] and [[blood type]]; in other words, all the genetic traits that vary between individuals. Genetic drift does not introduce new alleles to a population, but it can reduce variation within a population by removing an allele from the gene pool. Genetic drift is caused by random sampling of alleles. A truly random sample is a sample in which no outside forces affect what is selected. It is like pulling marbles of the same size and weight but of different colours from a brown paper bag. In any offspring, the alleles present are samples of the previous generationsgeneration's alleles, and chance plays a role in whether an individual survives to reproduce and to pass a sample of their generation onward to the next. The allelic frequency of a population is the ratio of the copies of one specific allele that share the same form compared to the number of all forms of the allele present in the population.<ref>{{harvnb|Futuyma|1998|p=Glossary}}</ref>

Genetic drift affects smaller populations more than it affects larger populations.<ref name="Ellstrand1993">{{cite journal |last1=Ellstrand |first1=Norman C. |last2=Elam |first2=Diane R. |date=November 1993 |title=Population Genetic Consequences of Small Population Size: Implications for Plant Conservation |journal=[[Annual Review of Ecology, Evolution, and Systematics|Annual Review of Ecology and Systematics]] |volume=24 |issue=1 |pages=217–242 |doi=10.1146/annurev.es.24.110193.001245|bibcode=1993AnRES..24..217E }}</ref>

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* {{cite book |last1=Carroll |first1=Sean B. |author-link1=Sean B. Carroll |last2=Grenier |first2=Jennifer K. |last3=Weatherbee |first3=Scott D. |year=2005 |title=From DNA to Diversity: Molecular Genetics and the Evolution of Animal Design |edition=2nd |___location=Malden, MA |publisher=[[Wiley-Blackwell|Blackwell Publishing]] |isbn=978-1-4051-1950-4 |lccn=2003027991 |oclc=53972564 }}

* {{cite book |last=Coyne |first=Jerry A. |author-link=Jerry A. Coyne |year=2009 |title=Why Evolution is True |___location=New York |publisher=[[Viking Press|Viking]] |isbn=978-0-670-02053-9 |lccn=2008033973 |oclc=233549529 |url=https://archive.org/details/whyevolutionistr00coyn }}

* {{cite book |last=Dalrymple |first=G. Brent |author-link=Brent Dalrymple |year=2001 |chapter=The age of the Earth in the twentieth century: a problem (mostly) solved |editor1-last=Lewis |editor1-first=C. L. E. |editor2-last=Knell |editor2-first=S. J. |title=The Age of the Earth: from 4004 BC to AD 2002 |journal=Geological Society, London, Special Publications |series=Geological Society Special Publication |___location=London |publisher=[[Geological Society of London]] |volume=190 |issue=1 |pages=205–221 |bibcode=2001GSLSP.190..205D |doi=10.1144/gsl.sp.2001.190.01.14 |isbn=978-1-86239-093-5 |s2cid=130092094 |lccn=2003464816 |oclc=48570033 }}

* {{cite book |last=Darwin |first=Charles |author-link=Charles Darwin |year=1859 |title=On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life |url=http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=text&pageseq=1 |edition=1st |___location=London |publisher=[[John Murray (publishing house)|John Murray]] |lccn=06017473 |oclc=741260650 }}

* {{cite book |last=Darwin |first=Charles |year=1872 |title=The Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life |url=http://darwin-online.org.uk/content/frameset?itemID=F391&viewtype=text&pageseq=1 |edition=6th |___location=London |publisher=John Murray |lccn=13003393 |oclc=228738610 }}

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* {{cite book |last=Mayr |first=Ernst |author-link=Ernst Mayr |year=1970 |title=Populations, Species, and Evolution: An Abridgment of Animal Species and Evolution |___location=Cambridge, MA |publisher=Belknap Press of Harvard University Press |isbn=978-0-674-69010-3 |lccn=79111486 |oclc=114063 |url=https://archive.org/details/populationsspeci00mayr }}

* {{cite book |last=Mayr |first=Ernst |year=2001 |title=What Evolution Is |url=https://archive.org/details/whatevolutionis0000mayr |url-access=registration |___location=New York |publisher=Basic Books |isbn=978-0-465-04426-9 |lccn=2001036562 |oclc=47443814 }}

* {{cite book |last=McKinney |first=Michael L. |year=1997 |chapter=How do rare species avoid extinction? A paleontological view |editor1-last=Kunin |editor1-first=William E. |editor2-last=Gaston |editor2-first=Kevin J. |title=The Biology of Rarity: Causes and consequences of rare—common differences |edition=1st |___location=London; New York |publisher=[[Chapman & Hall]] |isbn=978-0-412-63380-5 |lccn=96071014 |oclc=36442106 }}

* {{cite book |last1=Miller |first1=G. Tyler |last2=Spoolman |first2=Scott E. |year=2012 |title=Environmental Science |edition=14th |___location=Belmont, CA |publisher=[[Cengage Learning|Brooks/Cole]] |isbn=978-1-111-98893-7 |lccn=2011934330 |oclc=741539226 }}

* {{cite book |author=National Academy of Sciences |author-link=National Academy of Sciences |year=1998 |title=Teaching About Evolution and the Nature of Science |url=http://books.nap.edu/openbook.php?isbn=0309063647 |___location=Washington, D.C. |publisher=[[National Academies Press]] |isbn=978-0-309-06364-7 |lccn=98016100 |oclc=245727856 |access-date=2015-01-10 |ref=NAS 1998 }}

* {{cite book |author1=National Academy of Sciences |author2=Institute of Medicine |author-link2=Institute of Medicine |year=2008 |title=Science, Evolution, and Creationism |url=https://archive.org/details/isbn_9780309105866 |___location=Washington, D.C. |publisher=National Academies Press |isbn=978-0-309-10586-6 |lccn=2007015904 |oclc=123539346 |access-date=2014-07-31 |ref=NAS 2008 }}

* {{cite book |last=Raup |first=David M. |author-link=David M. Raup |year=1992 |orig-year=Originally published 1991 |title=Extinction: Bad Genes or Bad Luck? |others=Introduction by Stephen Jay Gould |journal=New Scientist |volume=131 |issue=1786 |pages=46–49 |___location=New York |publisher=W. W. Norton & Company |pmid=11540932 |isbn=978-0-393-30927-0 |lccn=90027192 |oclc=28725488 |url-access=registration |url=https://archive.org/details/extinction00davi }}

* {{cite book |last1=Raven |first1=Peter H. |author-link1=Peter H. Raven |last2=Johnson |first2=George B. |author-link2=George B. Johnson |year=2002 |title=Biology |url=https://archive.org/details/biologyrave00rave |url-access=registration |edition=6th |___location=Boston, MA |publisher=[[McGraw-Hill Education|McGraw-Hill]] |isbn=978-0-07-112261-0 |lccn=2001030052 |oclc=45806501 }}

* {{cite book |last=Tattersall |first=Ian |author-link=Ian Tattersall |year=1995 |title=The Fossil Trail: How We Know What We Think We Know About Human Evolution |url=https://archive.org/details/fossiltrailhowwe00tatt |url-access=registration |publisher=Oxford University Press |___location=New York |isbn=978-0-19-506101-7 |lccn=94031633 |oclc=30972979 }}