Extended Phenotype

The Extended Phenotype
Author Richard Dawkins
Subject Evolutionary biology
Publisher Oxford University Press
Publication date 1982
Pages 307
ISBN 0-19-286088-7
OCLC Number Dewey Decimal 575 20
LC Classification QH375 .D38 1983
Preceded by The Selfish Gene
Followed by The Blind Watchmaker

The Extended Phenotype (EP) is a biological concept introduced by Richard Dawkins in a 1982 book with the same title. The main idea is that phenotype should not be limited to biological processes such as protein biosynthesis or tissue growth, but extended to include all effects that a gene has on its environment, inside or outside of the body of the individual organism.

Dawkins considers the Extended Phenotype to be his principal contribution to evolutionary theory.[1]

Genes synthesize only proteins

In the main portion of the book, Dawkins argues that the only thing that genes control directly is the synthesis of proteins. He points to the arbitrariness of restricting the idea of the phenotype to apply only to the phenotypic expression of an organism's genes in its own body.

Genes do not affect the organism's body only

Dawkins develops this idea by pointing to the effect that a gene may have on an organism's environment through that organism's behaviour. Now it is commonly admitted that there are three types of EP. The first refers to the capacity of animals to modify their environment using architectural constructions. Dawkins cited as examples caddis houses and beaver dams.

He then goes further to point to first animal morphology and ultimately animal behaviour, which can seem advantageous not to the animal itself, but rather to a parasite which afflicts it. It is what we called : “parasite manipulation” which is the capacity of several groups of parasite to modify the host behavior to improve their fitness. One famous example of this second type of EP is the suicidal behavior of crickets infected by hairworm what increase the parasite reproduction success. Moreover such behaviour is seen, for example, in a study that found that female mosquitoes carrying malaria parasites are significantly more attracted to human breath and odours than uninfected mosquitoes. [2] However a recent study shows that an immune challenge with heat-killed Escherichia coli could generate the same changes in the behaviour than the infection by Plasmodium yoelii. It raises one question: in which extent the alteration of hosts behaviour is owing to active manipulation by malaria parasites? [3]

The last type of EP, instead of the second one, refers to an action at a distance of the parasite on its host. A common example is the manipulation of host behaviour by cuckoo chicks which are not physically associated with the host but influence the expression of its behavioural phenotype. [4]

Dawkins summarizes these ideas in what he terms the Central Theorem of the Extended Phenotype:


Gene-centred view of life

In conducting this argument, Dawkins aims to strengthen the case for a gene-centric view of life, to the point where it is recognized that the organism itself needs to be explained. This is the challenge which he takes up in the final chapter entitled "Rediscovering the Organism."

See also


External links

  • Video of cricket exhibiting behavioral extended phenotype of parasite
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