How different is macro/micro evolution

I used to argue (as several have here) that it is the same mechanism, that there is no difference, no barrier to macro evolution that is not broken by micro evolution -- and this is still true, butthat is because micro drives macrobut there are also different mechanisms at work, and this is where I've modified my opinion.If we look within a species population what we see as the mechanisms for evolution are (1) mutations and (2) natural selection. These are continually going on within all species, butwithin natural selection are some mechanisms that provide a trendency towards stasis, an averaging back of the population towards an median organism and deselection of extreme types, usually conveyed by sexual selection and by gene mixing -- the mutations that are not lethal or debilitating are shared around and spread from generation to generation.Once speciation has occurred however the population is divided, the gene mixing is cut off, and this allows for (but doesn't require) more rapid divergence from the old center.You can think of micro as all those selection mechanisms acting within a population, and macro as all those selection mechanisms acting between populations.Enjoy.

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Not exactly -- that's more of a result than a mechanism. To me it is a subtle little difference but important enough to consider.After a speciation separation, each population now has a new {stasis equilibrium} point that it will try to "center" (chose mates) around, and there is no mixing of genes between the divided populations so those {stasis equilibrium} points can diverge.But there are other population dynamics that are involved both before and after that are different. Take pelycodus: (Image copied to mirror site to save bandwidth originally from A Smooth Fossil Transition: Pelycodus)Where you see a general (normal) trend toward larger individuals as time passes, and then a speciation event with subsequest divergence between two populations. The right branch continues with the linear increase in size, however the left branch dives back to re-occupy the original {size\niche\function}. This would be forced by competition between the two groups, a selection pressure that doesn't happen while they are one population. Once they have diverged sufficiently that such competition does not threaten survival of one population, then each are free to take whatever evolutionary paths they want, but they will not be the same path - that bridge is burned.Note that the reduction in size is faster than the general increase in size. This is the effect of being de-linked.Note also that the population variation is restricted to the same general width rather than getting broader at each time level. This is the effect of the trendency towards stasis.Stasis doesn't have to be a result, btw, it can be {static relative to a continued trend} as above; it is just a tendency inherent in sexual selection (imho) towards average individuals in a population -- ie sexual selection could be a two-edged sword, allowing greater (liberal) mixing of genes along with quick (conservative) selection to omit extreme divergence.I tried to find the post where I had come to this conclusion last night and couldn't (silly ol search system + tired brain + impatience), but you can think of all the selection pressures that operate within a population and all the selection pressures that operate between populations as being the essential difference in the shape of the evolution that is observed.Wait, I finally found the post Which is further refined in You could also say that "micro" changes are not fixed in the population, as the population as a whole can revert under changed selection pressures (the way the beak size can revert). Whether the {features\alleles\variations} can become part of the defining characteristics of the species is debatable, as this gets into what distinguishes one species from another (especially on a timeline).Once a speciation has occurred those changes have become part of the {defining genome} of the species and so do become fixed (as part of the previous amount of variation is discarded in the divide), albeit still subject to "micro" changes around that {center\node\nexus}.Speciation is the dividing line then between "micro" and "macro" -- and once two speciation events occur in succession the fact that "macro"evolution (by this definition) has occurred cannot be denied either: that is all that is needed to show that evolutionary branches occur and that the result is a nested hierarchy, which is the basis of all upper level taxonomy divisions.You could also use the genetic differences between the species in these subsequent speciations and of their ancestors to validate the genetic tree derivations. I would think this has been done and that there would be ongoing work on it to refine the marker systems used (anybody know of papers on this?).You can't have "macro" without "micro" -- the basic mechanism of change is still the same -- but you could have "micro" without "macro" ... hence evidence of such effect is different than evidence of (species) change over time.Hope that helps.Enjoy.Edited by RAZD, : added (species) at end

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