Wednesday, 26 May 2010

Microevolution & Macroevolution

This is not the most thorough description of the differences as I thought I would share some of the "off-the-cuff" answers I gave on a Facebook discussion recently. After the typical creationist claim of "I accept microevolution but not macroevolution" someone stated that there is no difference between microevolution and macroevolution, so I decided to clear things up, here was my response:

On micro and macro evolution there is a distinction within the scientific community, but not the way creationists would like. One embraced by all evolutionists is that micro and macro both employ different techniques in order to study them; micro uses observable experimentation, whereas macro generally uses the fossil record and genomic comparison for example, though there is overlap occasionally between the two studies. 

The other distinction is the debated one. Many evolutionists believe that macro is simply micro added up (the difference is quantitative), whereas some believe other processes are at work during macroevolution and that there is a qualitative difference (extrapolation is therefore not justified). Processes in the latter include species selection, though this view is the minority. Both sides affirm that macroevolution can and does occur, they merely disagree on how.

I was then asked which distinction of macroevolution (referring to my second paragraph) seems to be evidently accurate, to which I responded: 

A bit of both in my opinion. Species selection is plausible but difficult to demonstrate. The argument centres around speciation really and whether or not it is the locus of major evolutionary change. I take the view that micro adds up to macro but that at times speciation locks in change (this fits into the first of the two views I gave) though I also think that there may be circumstances where species selection plays a part and prevents simple extrapolation. For all intents and purposes, and for a shorter answer, I believe extrapolation of micro to macro is valid in most cases. 

I later decided to expand even further, just in case:

To expand on my point about the differences between micro and macro evolution, just in case someone misunderstands it and thinks I am saying that we do not understand how micro can add up to macro, I think it is worth mentioning that the issue comes from our understanding of natural selection. If natural selection works only on the level of genes and individuals (and modules perhaps...oooh....controversial) then micro extrapolates up to macro no problem. However, if it works on other levels, not necessarily group selection, but certainly species selection (and dare I mention clade selection?) then the extrapolation is unjustified. Considering the levels/units of selection is an abstract concept, it is no surprise that there is disagreement about it. Demonstrating which occurs is not always easy and often requires mathematical arguments to back any experimental evidence and vice versa.

I could expand on this enormously to be honest as a lot of the content needs more development and clarification; put this on the list for the future maybe? If you are interested in more on this subject, I recently wrote a piece which discussed levels of selection in brief, titled A New Type of Selection? And quite a while ago I wrote a piece about punctuated equlibrium, a topic which overlaps with this one to a significant degree. It was called Punctuated Equilibria Explained (or PEE if you like...).

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