When organisms evolve together based on mutualistic relationships. The organisms both benefit from their interaction with one another. They may rely on each other for things like nutrients or protection.[]
"Natural selection cannot possibly produce any modification in a species exclusively for the good of another species" (Darwin, On the Origin of Species)- Here Darwin argues that altruism between species doesn't exist, that instead, natural selection will produce modifications that can benefit another species while also benefitting the original species.
Symbiotic mutualism: When two different species are involved with one another for the bulk of their life span (Futuyma, 2005). []
Examples: []
Mycorrhizal fungi and plants- while this relationship can be considered mutualistic when soil is infertile, it can be parasitic and reduce plant growth when soil is fertile (Futuyma, 2005).
Lichens
Clown fish & Sea anemone (http://bio4esobil2011.wordpress.com/2012/05/27/mutualism/)
Bee & Flower http://bio4esobil2011.wordpress.com/2012/05/2
Darwin, C. (2003). On the Origin of Species: A Facsimile of the First Edition. Cambridge, MA: Harvard University Press.
Futuyma, D. (2005). Evolution. Sunderland, MA: Sinauer Associates, Inc.