Naturlig selektion kan fungere på forskellige niveauer af biologisk organisation, såsom gener, celler, individuelle organismer, grupper af organismer og arter.<ref name="Okasha07">{{harvnb|Okasha|2006}}</ref><ref name="Gould">{{cite journal |last=Gould |first=Stephen Jay |author-link=Stephen Jay Gould |date=28. februar 1998 |title=Gulliver's further travels: the necessity and difficulty of a hierarchical theory of selection |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |location=London |publisher=Royal Society |volume=353 |issue=1366 |pages=307–314 |doi=10.1098/rstb.1998.0211 |issn=0962-8436 |pmc=1692213 |pmid=9533127}}</ref><ref name=Mayr1997>{{cite journal |last=Mayr |first=Ernst |author-link=Ernst Mayr |date=18. marts 1997 |title=The objects of selection |journal=Proc. Natl. Acad. Sci. U.S.A. |location=Washington, D.C. |publisher=National Academy of Sciences |volume=94 |issue=6 |pages=2091–2094 |bibcode=1997PNAS...94.2091M |doi=10.1073/pnas.94.6.2091 |issn=0027-8424 |pmc=33654 |pmid=9122151}}</ref> Selektion kan agere på flere niveauer samtidigt.<ref name="Smith1">{{harvnb|Maynard Smith|1998|pp=203–211; discussion 211–217}}</ref> Et eksempel på selektion, som forløber under niveauet for den individuelle organisme, er gener kaldet [[transposon]]er, som kan replikkere og sprede sig i et genom.<ref name="Hickey1">{{cite journal |last=Hickey |first=Donal A. |year=1992 |title=Evolutionary dynamics of transposable elements in prokaryotes and eukaryotes |journal=[[Genetica]] |location=Dordrecht, the Netherlands |publisher=[[Springer Science+Business Media|Kluwer Academic Publishers]] |volume=86 |issue=1–3 |pages=269–274 |doi=10.1007/BF00133725 |issn=0016-6707 |pmid=1334911}}</ref> Selektion på et niveau over individer, såsom [[gruppe selektion|gruppeselektion]], kan tillade evolution af et samarbejde mellem individer.<ref name="Ghould1">{{cite journal |last1=Gould |first1=Stephen Jay |last2=Lloyd |first2=Elisabeth A. |author-link2=Elisabeth Lloyd |date=12. oktober 1999 |title=Individuality and adaptation across levels of selection: how shall we name and generalise the unit of Darwinism? |journal=Proc. Natl. Acad. Sci. U.S.A. |location=Washington, D.C. |publisher=National Academy of Sciences |volume=96 |issue=21 |pages=11904–11909 |bibcode=1999PNAS...9611904G |doi=10.1073/pnas.96.21.11904 |issn=0027-8424 |pmc=18385 |pmid=10518549}}</ref>
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