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Friday, March 28, 2008

Macroevolution and microevolution

Some Christians who think about origins have no trouble believing that varieties, perhaps even species, have come about through natural selection. They call this microevolution. The same people may have difficulty, for various reasons, believing that a whole phyum, say, Chordates, evolved from some other group, which would be an example of macroevolution. Some criticize such beliefs, saying that there is no difference between micro- and macro-evolution, and claim that Christians invented these two terms, and that they are unnecessary.

However, the distinction has some merit. There is a Wikipedia article on macroevolution, and, according to it, there has been some use of the term, including its invention, by mainstream scientists, for other than religious reasons. The article does not support the idea that new groups have come about by other than natural selection.

There are some people who do doubt that new groups came about this way, for several reasons, some of them religious, of course.

One reason is the many phyla discovered in the fossils of the Burgess shale, which, according to some authors, arose all at once with no known fossil ancestors. I'm not sure that that helps those who disbelieve that new groups came about by Darwinian selection, but, rather, by divine creation, though. Why did God create whole phyla that soon became extinct?

Another reason is logical. How could, say, a forelimb that was intermediate between a walking reptilian leg and a flying bird wing give any advantage to a creature (if there were any such) who possessed such an appendage, over its ancestral types, which walked on four limbs? It would not, seemingly, aid in either flight or walking. A number of like transitions can be imagined, and it is not always easy to come up with reasonable intermediate steps. This doesn't prove that the intermediates weren't there, of course.

Another reason is,of course, that some people believe that there hasn't been enough time for large changes caused by natural selection.

It seems to me that macro- and microevolution are legitimate terms.

Thanks for reading.

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