Intelligent design proponents make a negative argument for design. According to them, the complexity and diversity of life cannot be accounted for by unguided evolution (henceforth referred to simply as ‘evolution’) or any other mindless natural process. If it can’t be accounted for by evolution, they say, then we must invoke design. (Design, after all, can explain anything. That makes it easy to invoke, but hard to invoke persuasively.)
Because the ID argument is a negative one, it succeeds only if ID proponents can demonstrate that certain instances of biological complexity are beyond the reach of natural processes, including evolution. The problem, as even IDers concede, is that the evidence for evolution is too strong to dismiss out of hand. Their strategy has therefore been to concede that evolution can effect small changes (‘microevolution’), but to deny that those small changes can accumulate to produce complex adaptations (‘macroevolution’).
What mysterious barrier do IDers think prevents microevolutionary change from accumulating until it becomes macroevolution? It’s the deep blue sea, metaphorically speaking. IDers contend that life occupies ‘islands of function’ separated by seas too broad to be bridged by evolution.
In this post (part 2a) I’ll explain the ‘islands of function’ metaphor and invite commenters to point out its strengths and weaknesses. In part 2b I’ll explain why the ID interpretation of the metaphor is wrong, and why evolution is not stuck on ‘islands of function’.
Read on for an explanation of the metaphor.
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