Sunday, January 09, 2005

Evolution of Phenotype and Genotype.

I went to the National Academy of the Sciences' meeting in honor of Ernst Mayr. The general topic was "Systematics and the Origin of the Species," the title of Mayr's publication from 1942. There were talks by Howard Ochman, Allen Orr, Jody Hey, among many other prominent biologists studying speciation, but one talk by Mary Jane West-Eberhard stood out to me.

Dr. West-Eberhard's talk, entitled "Developmental Plasticity and Evolutionary Innovation," was particularly interesting. She used quadruped mammals that have learned to walk bipedaly due to injuries that prevented them from using the front limbs as an example of developmental plasticity. She argued that these learned behaviors could have evolutionary implications if they provided a benefit to those individuals that were able to learn them. In a way, she was speaking about memes (learned rather than inherited behaviors) sweeping through a population.

Needless to say, this produced quite a stir among a few folks who viewed this as an example of Lamarckian evolution -- the evolution of acquired characteristics. But Dr. West-Eberhard's point was not that inheritance of genetically encoded traits is unimportant, rather that these learned characters could shape the organism's environment and, therefore, alter the selective landscape and lead to genetic evolution.

It's a rather innovative way of looking at drastic phenotypic evolution that avoids "hopeful monster" type mutations in favor of behaviors that can drastically change phenotype. I assume (I am not entirely familiar with the model and my only exposure to it comes from the one talk I attended) that when an individual acquires a new (successful) behavior and other individuals mimic it, natural selection will favor alleles that are more fit with this novel behavior. It's almost like a population moving to a new environment with different selective pressures, so that natural selection changes the allele frequencies from that in the old environment to the new one (remember, fitness is only relevant in relation to the environment and the other alleles present in a population).

As an example, one can think of primitive bipedal primates (our ancestors) moving out of the trees in the African rain forest and into the flatlands. It may be possible that a population learned to walk upright without any drastic mutations, and they were able to exploit an open niche on the jungle floor. Next, either new mutations or existing alleles were selected for that increased the fitness of these bipedal individuals, and, over time, there was a strong genetic component to bipedal locomotion that initial arose through purely environmental/behavioral means. Pretty neat, huh?

I may be getting some of the details wrong (I'm not an expert on the subject), but I wanted to get these ideas down since they seem pretty cool. Also, it's a nice F.U. to those intelligent design/creationists who argue that evolutionary biologists are constrained by their dogma and unwilling to accept new ideas. This hypothesis (unlike ID) is testable and scientifically workable, which means it's worthy of publishing in peer-reviewed journals and worth discussing and scientific meetings. And it looks like Lamarck may not have been entirely wrong after all!


At 2:33 PM, Blogger coturnix said...

This model has been worked out in quite a lot of detail by Odling-Smee in his series of papers on "niche-construction" - great reads all.

At 12:18 PM, Blogger RPM said...

I think West-Eberhard's model goes beyond niche construction in that she postulates that major morphological evolution can be shaped by behavioral changes that arise through phenotypic plasticity. It appears to be a distinction between micro vs. macroevolution -- and I know a lot of people don't like those terms since they're heavily used by creationist and IDists.

At 1:35 PM, Blogger RPM said...

Also, see Dr. West-Eberhard's book, Developmental Plasticity and Evolution


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