Editing Evolution (section)

=== Cooperation ===
{{Further|Co-operation (evolution)}}

Not all co-evolved interactions between species involve conflict.<ref>{{cite journal |last=Sachs |first=Joel L. |date=September 2006 |title=Cooperation within and among species |journal=Journal of Evolutionary Biology |volume=19 |issue=5 |pages=1415–1418; discussion 1426–1436 |doi=10.1111/j.1420-9101.2006.01152.x |pmid=16910971 |s2cid=4828678}}
* {{cite journal |last=Nowak |first=Martin A. |author-link=Martin Nowak |date=8 December 2006 |title=Five Rules for the Evolution of Cooperation |journal=Science |volume=314 |issue=5805 |pages=1560–1563 |bibcode=2006Sci...314.1560N |doi=10.1126/science.1133755 |pmc=3279745 |pmid=17158317 |ref=none}}</ref> Many cases of mutually beneficial interactions have evolved. For instance, an extreme cooperation exists between plants and the [[mycorrhiza]]l fungi that grow on their roots and aid the plant in absorbing nutrients from the soil.<ref>{{cite journal |last=Paszkowski |first=Uta |date=August 2006 |title=Mutualism and parasitism: the yin and yang of plant symbioses |journal=Current Opinion in Plant Biology |volume=9 |issue=4 |pages=364–370 |doi=10.1016/j.pbi.2006.05.008 |issn=1369-5266 |pmid=16713732 |bibcode=2006COPB....9..364P}}</ref> This is a [[Reciprocity (evolution)|reciprocal]] relationship as the plants provide the fungi with sugars from [[photosynthesis]]. Here, the fungi actually grow inside plant cells, allowing them to exchange nutrients with their hosts, while sending [[signal transduction|signals]] that suppress the plant [[immune system]].<ref>{{cite journal |last1=Hause |first1=Bettina |last2=Fester |first2=Thomas |s2cid=20082902 |date=May 2005 |title=Molecular and cell biology of arbuscular mycorrhizal symbiosis |journal=[[Planta (journal)|Planta]] |volume=221 |issue=2 |pages=184–196 |doi=10.1007/s00425-004-1436-x |pmid=15871030 |bibcode=2005Plant.221..184H}}</ref>

Coalitions between organisms of the same species have also evolved. An extreme case is the [[eusociality]] found in social insects, such as [[bee]]s, [[termite]]s and [[ant]]s, where sterile insects feed and guard the small number of organisms in a [[Colony (biology)|colony]] that are able to reproduce. On an even smaller scale, the somatic cells that make up the body of an animal limit their reproduction so they can maintain a stable organism, which then supports a small number of the animal's germ cells to produce offspring. Here, somatic cells respond to specific signals that instruct them whether to grow, remain as they are, or die. If cells ignore these signals and multiply inappropriately, their uncontrolled growth [[carcinogenesis|causes cancer]].<ref name="Bertram-2000">{{cite journal |last=Bertram |first=John S. |date=December 2000 |title=The molecular biology of cancer |journal=[[Molecular Aspects of Medicine]] |volume=21 |issue=6 |pages=167–223 |doi=10.1016/S0098-2997(00)00007-8 |pmid=11173079 |s2cid=24155688}}</ref>

Such cooperation within species may have evolved through the process of [[kin selection]], which is where one organism acts to help raise a relative's offspring.<ref>{{cite journal |last1=Reeve |first1=H. Kern |last2=Hölldobler |first2=Bert |author-link2=Bert Hölldobler |date=5 June 2007 |title=The emergence of a superorganism through intergroup competition |journal=PNAS |volume=104 |issue=23 |pages=9736–9740 |bibcode=2007PNAS..104.9736R |doi=10.1073/pnas.0703466104 |issn=0027-8424 |pmc=1887545 |pmid=17517608 |doi-access=free}}</ref> This activity is selected for because if the ''helping'' individual contains alleles which promote the helping activity, it is likely that its kin will ''also'' contain these alleles and thus those alleles will be passed on.<ref>{{cite journal |last1=Axelrod |first1=Robert |last2=Hamilton |first2=W. D. |date=27 March 1981 |title=The evolution of cooperation |url=https://archive.org/details/sim_science_1981-03-27_211_4489/page/1390 |journal=Science |volume=211 |issue=4489 |pages=1390–1396 |bibcode=1981Sci...211.1390A |doi=10.1126/science.7466396 |pmid=7466396}}</ref> Other processes that may promote cooperation include group selection, where cooperation provides benefits to a group of organisms.<ref>{{cite journal |last1=Wilson |first1=Edward O. |last2=Hölldobler |first2=Bert |date=20 September 2005 |title=Eusociality: Origin and consequences |journal=PNAS |volume=102 |issue=38 |pages=13367–1371 |bibcode=2005PNAS..10213367W |doi=10.1073/pnas.0505858102 |pmc=1224642 |pmid=16157878 |doi-access=free}}</ref>