Re: Extended Phenotype as Adaptive Niche
I'm a bit more than halfway through The Extended Phenotype
, but I'll take a stab at your question, Robert.
Normally when you talk about phenotype, it's the expression of genes or observable characteristics of an individual
related to its interaction with the environment.Wikipedia:
- Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and possible interactions between the two. The genotype of an organism is the inherited instructions it carries within its genetic code. Not all organisms with the same genotype look or act the same way because appearance and behavior are modified by environmental and developmental conditions.
But this definition is individual-centric. As you know, Dawkins promotes the idea of seeing things from a gene's perspective which changes things profoundly. If you look at it this way, the gene's environment includes other
genes. InThe Selfish Gene
, Dawkins presents the idea that a gene's success frequently depends on how it interacts with other genes. Remember the analogy of the rowers in a boat, and how a gene can be affected by both its position in the boat and how it's output can be affected by the positions of other rowers? But the gene's environment is also the body in which it sits, a concept Dawkins explains quite well in the added on last chapter of The Selfish Gene
, "The Long Reach of the Gene." The italics in the quoted passage are Dawkins'.
"The phenotypic effects of a gene are normally seen as all the effects that it has on the body in which it sits. This is the conventional definition. But we shall now see that the phenotypic effects of a gene need to be thought of as all the effects that it has on the world.
It may be that a gene's effect, as a matter of fact, turn out to be confined to the succession of bodies in which the gene sits. But, if so, it will be just as matter of fact. It will not be something that ought to be part of our very definition. In all this, remember that the phenotypic effects of a gene are the tools by which it levers itself into the next generation. All that I'm going to add is that the tools may reach outside the individual body wall. What might it mean in practice to speak of a gene as having an extended phenotypic effect on the world outside the body in which it sits? Examples that spring to mind are artefacts like beaver dams, bird nests, and caddis houses." (pg. 238)
These are obvious examples, but i think Dawkins is also suggesting that the shape of a caddis house is not really different than the shape of a leg or antenna of the individual caddis. Both are phenotypic effects that a gene has on the world (from a gene's perspective). It doesn't matter so much whether that phenotypic effect takes place in the body in which the gene sits or in the world at large. I think
what Dawkins means by "extended phenotype" is a gene's reach into the environment outside of the body in which it sits. So Robert provides some good examples. A spider's web or a tree that creates a canopy and creates a shaded area which limits other types of plant growth are others. Also the way some parasites actively affect the DNA of its host organism is yet another.