Nick, I think I agree with you. You say "So whether relaxed selection produces 'exploration of morphology space' will depend on the structure and stability of the environment in terms of size and longevity of the species."
If the evidence, that S J Gould brought to everyone's attention, is that speciation occurs typically by a rapid spurt of evolutionary change, or alternately in a confined ecology, or both, a time & space confinement, that describes bounds within which the genetic mould is somehow relaxed and resolidified. The question is if it occurs maybe once in a period of a million years for each species... and for just one of perhaps thousands of species in the same environment at a time, what would be required to do that?? Phil > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > Behalf Of Nicholas Thompson > Sent: Thursday, October 09, 2008 11:37 PM > To: friam@redfish.com > Subject: [FRIAM] Relaxed Selection, a b-level posting > > Russell Standish offered the following question: > > > > What do you think of "relaxed selection" ? > > My inexpert response: > > Well, I am uneasy about the concept. When I used to be a teacher of > these > things, students LOVED the idea that some ages and places are harsh and > some are mellow, and that selection is relaxed in the latter. The > metaphor > is drawn, I assumed, from human economics, where some decades can be > easy > and some difficult. But the metaphor is dangerously misleading ... > [thompson loves metaphors but he loves some metaphors a whole lot less > than > others, and this one is a terrible one.] The metaphor is terrible > because > the time-scale of oscillations of good and bad times in economics is > WAY > too short for the reproductive capacity of the species to respond. So > the > "times" are sort of independent of the reproduction of the species. > > But in the evolutionary time scale, whether times are good and bad is > determined not by how lush the environment but by whether the > environment > has been lush long enough for the reproductive potential of the species > to > catch up and de-lush it. So rather than think about "good times" in > evolution, I would tend to think of periods of rapid expansion of > populations (when selection is relaxed) and rapid contraction of > populations (when selection is intensified) and periods of stability > (when > selection is intermediate.) > > One of your respondents seemed (sorry, too lazy to go back and look) to > confound this issue with the question of how bushy or trunky the > evolutionary tree is. I dont think... that the two are related. Bushy > phylogenies ... like that of australopithecines (the bipedal apes that > were > around as genus homo was coming into being) would seem to be generated > by > the distribution of the species over a spatially variant but temporally > invariant landscape. Trunky phylogenies are produced by the > distribution > of the species over temporally variant and a spacially invariant > landscape. This latter pattern characteried the evolution of the genus > homo. The attributions of variance and invariance, of course, have to > be > made in terms of the longevity of the species and its tendancy to move > accross the landscape. > > So whether relaxed selection produces "exploration of morphology space" > will depend on the structure and stability of the environment in terms > of > size and longevity of the species. > > That's what I think of relaxed selection. Apologies if I have been > reading > carelessly. > > NIck > > Nicholas S. Thompson > Emeritus Professor of Psychology and Ethology, > Clark University ([EMAIL PROTECTED]) > > > ************************************* > > > > ============================================================ > FRIAM Applied Complexity Group listserv > Meets Fridays 9a-11:30 at cafe at St. John's College > lectures, archives, unsubscribe, maps at http://www.friam.org ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org
