I agree with most of Nick's hesitations (except re: all caps.. :-)) Population expansion would increase the variety of individuals to be selected from, though. I think that was the idea behind Terry Deacon's theory, still with variation being random and constant, and using the same old tautology that change is caused by what survives. That there are several levels of (mostly unexplained) organization and the need for selection to somehow differentiate between them, and to do so differently for every organism in the environment, has always been a problem for me in seeing selection as the primary hand of 'design'. When I build things that way it never works. Still, if there are times of great variety in emerging designs and generous environmental capacities for all to flourish, one of the newbies may be the one that survives when the tide turns to drought and famine. That's sure how it works in economies, and ecologies are indeed natural economies.
One thing I don't see addressed by changing selective pressures to vary rates of evolution is the possibility of, and apparent need for, 'mutations' that have low rates of destroying the whole organism. Punctuated equilibrium seems to imply that there are rare periods when the success rate of diverse interrelated mutations is a lot higher than the rest of the time. That there is some kind of switch that turns whole system malleability on and off. If you just had a little greater likelihood of mutations at the periphery of the genome's design, whatever that is, in preference to it's central structures, it would produce a lot more variation in functional design in proportion to dysfunctional design. In that plankton paper of mine I also broadly speculate on particular mechanisms for that. That seems to be the same issue Kirschner and Gerhart are getting at when subtitling their book "resolving Darwin's dilemma" and by some of the other EvoDevo models I keep hearing about where variation trees rather than random disruptions are the key to inventing new things that work . Phil From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Nicholas Thompson Sent: Monday, October 13, 2008 2:18 PM To: friam@redfish.com Subject: [FRIAM] Selection, Reproductive rate, and Karrying Kapacity. All, Here are some comments on various comments. I succumb, reluctantly, to the community norm about caps. [grumble, grumble] Glen Said ====> The idea of expansion and contraction is interesting: rapid expansion of populations (when selection is relaxed) vs. rapid contraction of populations (when selection is intensified). The human population went indeed through a phase of rapid expansion in the last decades while natural selection was released through cultural and technological progress. Seed Magazine has an article about human evolution and relaxed selection, too <http://www.seedmagazine.com/news/2008/10/how_we_evolve_1.php> http://www.seedmagazine.com/news/2008/10/how_we_evolve_1.php <=== Nick Replies ===> I think this is a confusion between carrying capacity and selection. When, for some reason, carrying capacity is increased, the whole population can expand, but this does not stop selection. It may change the nature of selection from tracking how well individuals can make use of limited resources to how fast they can reproduce when times are flush, but there is no reason to think that raising the carrying capacity should "relax" selection. Russell Wrote ===> Any extinction event is a collapse of the food web. And selection only proceeds by means of extinction. So I'm not really quite sure what you're trying to nuance here. Nick Replies ===> OK. Here is where we disagree, I think. Let's worry this a bit, before we talk about anything else, because it seems absolutely central: When talking about selection, at what level of organization are we speaking? Gene, individual, small group, "deme", species, ecosystem? etc. I grew up under the influence of George Williams who argued that no entity above the individual could serve as a level of selection and of Richard Dawkins, who argued that no entity above the level of the gene could serve as a level of selection. So, in my world, species level selection is not a powerful cause of evolution. Indeed, on some definitions, species, by definition, cannot compete. Now, in the last decade, I have thrown off Williams' shackles and started to talk about selection at the level of the small group. And, indeed, I do know that some others have started talking about species-level selection. But species level selection has not become the received view, has it???? If not, the statement above must be EXTREMELY [whoops, _extremely_] controversial. Let's pause here and see what others say. Nick Nicholas S. Thompson Emeritus Professor of Psychology and Ethology, Clark University ([EMAIL PROTECTED])
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