Streams, creeks, rivers, lakes and oceans

The Stand to Reason blog had a short article a while back on the classic creationist argument about microevolution versus macroevolution.

Sure, everyone believes those examples of “evolution.” That’s microevolution. That’s not controversial.

Perhaps the reason so many Americans are unconvinced of evolution is because these examples hardly explain what needs to be explained – macroevolution. This is the process by which a single cell evolves into the myriad of living organisms that exist today without any intelligent intervention.

I’d like to illustrate what’s wrong with this argument using streams, creeks, rivers, lakes and oceans.

The fundamental problem with the creationist “micro vs macro” argument is that the terms microevolution and macroevolution refer, not to different processes of evolution, but to the results of evolution as seen across different timescales. That is, there is not a microevolution process and a macroevolution process, there is only an evolution process, whose results are called “micro” when you compare samples that are relatively near to each other, and “macro” when you compare samples that are more widely separated.

The process is analogous to the relationship between tiny streams, larger creeks, even larger rivers, and even larger bodies of water like lakes and oceans. We have different names for these phenomena, but in a way they’re all the same process: water flowing downhill. It would be silly to treat rivers and oceans as being something categorically different from creeks and streams, just like it’s nonsensical to treat microevolution and macroevolution as though they were categorically different.

Trying to accept microevolution while denying macroevolution is like trying to admit that creeks and streams exist while denying the existence of rivers and oceans. A river is just the result of many smaller streams flowing together, so you can’t really accept the stream and then deny the consequence of the streams’ existence. In the same way, macroevolution is simply the consequence of many microevolutionary changes accumulating over time. You can’t (legitimately) accept the fact of microevolution and then credibly deny its consequences.

 
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Posted in Science. 2 Comments »

2 Responses to “Streams, creeks, rivers, lakes and oceans”

  1. postdiluviandiaspora Says:

    This isn’t entirely correct. See here: http://sandwalk.blogspot.com/2007/11/with-friends-like-this.html

  2. The Professor Says:

    That’s an interesting point, but I think Larry Moran is speaking about a distinction that exists at a much more detailed and technical level than what I’m referring to. Biologists aren’t content with understanding that natural variation coupled with natural selection can produce different species over time, via common descent. Modern biologists want to understand exactly what mechanisms produce the variations, and exactly what circumstances produce the natural selection, and how different combinations of circumstances produce measurable differences in the rate of change and the propagation of new characteristics and so on. At that level of detail, it might make sense to differentiate between processes that produce quantitatively different rates of change, but it’s still a more or less arbitrary distinction, with fuzzy boundaries. It’s a difference of degree rather than category.

    This blog takes a more high-level, layman’s approach to such topics, however. At that level, I think it’s still reasonably accurate (if slightly over-simplified) to point out that we’re still talking in terms of the same types of fundamental mechanisms: variations arise naturally, and the distribution of different characteristics varies from one generation to the next based on how those characteristics contribute, or fail to contribute, to the reproductive success of the individual possessing them.

    “Macro” evolution and “micro” evolution both work by deriving new species from common ancestors. It’s not as though microevolution worked by evolving new species from common ancestors, and macroevolution involved some kind of different process that led modern amphibians, say, to suddenly give birth to modern lizards (i.e. making a horizontal leap across two separated branches of the tree of life). Both micro and macro are deriving new species from older ones. So in that sense I would still argue that one cannot reasonably accept the fact of microevolution and deny the fact of microevolution. There are no barriers to evolution that would prevent the micro changes from accumulating over time. Biologists are simply working out the details of the timing.