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Dawkin’s “extended phenotype”, an extension or a revolution?

Posted by: Issa Abu-Dayyeh

The extended phenotype, a relatively longer and a more difficult reading than Dawkin’s “The selfish gene”, is in my opinion a book worth the reading effort for several reasons:

1-Although a big portion of the book was dedicated to rebuttal critics that showered Dawkins with accusations of being a genetic determinist and a reductionist (Based on his views in the Selfish gene), Dawkin’s replies to those criticisms are pretty logical and organised. In fact, Dawkins almost did not have to retract any of the claims he made 6 years before “the extended phenotype” was written.

2-The rest of the book sets to establish a new vision on the extent to which a gene can act.

Many of us would agree that an organisms’ behaviour is selected to maximize the success of the replication of the genes residing inside this organism. As tempting as this statement might be, this vision definitely pictures the body as the gene’s prison. It is the boundary, the wall,the farthest limit upon which a gene can act.

Dawkins suggests in “the extended phenotype” that the action of genes goes way beyond their ability to produce proteins for the bodies they reside in. In fact, genes can have effects on inaminate objects (such as the type of house an animal would build) or on other living beings. An example given by Dawkins is a trematode that lives in snails. This trematode codes for proteins that drive the snail to produce thicker shells than ususal. This provides greater protection for the trematode while diverting the snail’s energy from practices that could benefit the snail but not the trematode such as: reproduction. The author goes on and on giving examples of how genes can act at a distance!

But how influential is this extended phenotype argument? After reading the book, my initial thought was that it is really no revolution! This is simply an extension of our vision of how far genes should be seen to go. On a deeper thought, I believe this book is revolutionary from a different perspective. First, it places more emphasis on the interactions of genes (regardless of the organism that carries them) on the overall evolution of complex traits and the natural selection they undergo. The principle also explains how a parasite can alter the host’s behaviour to its advantage (therefore suggesting what was formerly thought as mal-adaptation of a host gene as good adaptation of the parasite gene), and how some parasites can end up as symbionts and ultimately interested in increasing the reproductive success of the host and, soon, very difficult to even be seen as  parasites (ex: the mitochondria and chloroplast endosymbiont theory).

This book simply modifies a vision: from behaviour maximizing the success of the genes inside the organism to behaviour maximizing the success of genes that code for that specific behaviour, no matter in whose body those genes are found. This definition reorganizes the genetic vision in a way highly compatible with dawkins’ selfish gene view of evolution and natural selection. Is he right about the extended phenotype or is he wrong? I think most of us would agree it is a logical extension of what we perceive as a direct effect of a gene, but what really matters is that it is different… and a different view is sometimes what we need to reevaluate our current vision and devise new experiments to expand our knowledge. Not to mention the importance of such a vision on the mathematics of genetic contributions to phenotypes. In a nutshell, this is a book worth reading!

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