January 19, 2009
Evolutionary Biologists Support Extended Phenotype Concept
Richard Dawkins' Extended Phenotype (EP) concept is as relevant now as when it was first proposed 26 years ago and is not at odds with other evolutionary explanations. This was the conclusion of a recent workshop on the Extended Phenotype today, organized by the European Science Foundation (ESF).
The EP states that the genes of an organism can be expressed beyond its immediate biological boundary, extending for example to birds' nests, or the behavior of hosts infected by parasites. The key point is that the EP embraces constructions, such as the dams built by beavers, whose quality is correlated with variations, or alleles, in certain of the organism's genes, so that natural selection can act upon them. A new allele that leads to better dam constructions will in turn benefit the beaver expressing it. Similarly a parasite allele that causes the behavior of its host to change in a way that increases the parasite's chance of survival will be favored.Dawkins regarded EP as his single most important contribution to evolutionary biology, but since its publication in 1982, other theories have emerged and questions have arisen over its own fitness for survival. Any doubts were dispelled at the ESF conference, which resurrected EP as an important and valuable concept that helps explain evolution, even though it does not actually help predict specific outcomes.
"It was recognized that it has explanatory rather than predictive power," said David Hughes, convenor of the ESF workshop, from the Department of Biology, University of Copenhagen, now at Harvard. "It is a good way of looking at things but not necessarily the best approach when designing experiments."
The idea that niche construction, often considered as a rival theory, contradicted EP was dismissed. "It was agreed that other currently topical points of debate such as Niche Construction theory had no major conflict with the EP," said Hughes.
However there was lively debate between Dawkins and proponents of niche construction over the role of evolution within closely coupled ecosystems. Niche construction theory goes further than EP by suggesting that organisms can alter the selective pressures acting on them by modifying their environment in many ways beyond immediate constructions such as beaver dams. In niche construction theory, the link between variations in an organism's genes and in the surrounding environment is more loosely coupled with no clear mechanism for natural selection to operate.
However according to niche construction theory, there is a feedback effect, in that the genes of organisms alter the environment indirectly, for example by improving nests, that in turn modifies the selective pressures on those genes. Dawkins argued that niche construction is really a special case of EP, relating to genes of those organisms that participate in the relevant environmental construction. But he dismissed the idea that evolution can act in a broader sense across a whole ecosystem, extending to organisms not directly involved in the niche construction. He reiterated the point running through all his books, that selection can only operate against variation of replicators, which are almost always alleles (variants) of genes. The variation in genes caused by mutation generates the different phenotypes, characteristics such as animal behavior, that allow natural selection to work.
Some advocates of niche construction have suggested that evolution can operate at longer range. For example beavers construct dams that might benefit other animals not directly associated with them. While this may be the case, Dawkins has consistently argued that this would not result in behavior that would help select genes in beavers themselves that would lead to better dams. Only organisms whose response to better dams has a direct benefit for beavers can affect selection of beaver genes, Dawkins argues.
These points were accepted at the ESF workshop, which concluded that the EP was fine as it stood with no need of revision. Moreover, it emerged that recent research on metabolism had reinforced the EP concept, in particular by showing how closely the health of mammals including humans depends on the populations of microbes, especially bacteria, in the gut. EP might help understand how these populations have evolved in concert with mammals.
Ideas for further projects were proposed. "A follow up funding application is a great idea and it should focus on examining the parasite manipulation of host behavior component," said Hughes. "There was also a suggestion to have a separate application for a nest construction pan-EU network." These programs would be truly European, typically involving 5-7 partners across the EU.
The ESF Explanatory Workshop, The New Role of the Extended Phenotype in Evolutionary Biology, was held in Copenhagen, Denmark, 2-5 November 2008.
On the Net:
- European Science Foundation
- Workshop: The New Role Of The Extended Phenotype In Evolutionary Biology
- The Extended Phenotype - Wikipedia