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Phinehas asks Neil Rickert a fascinating question about the supposed direction of evolution. Neil says he will address it in a separate thread, and I started this one for that purpose. The rest of the post is Phenehas’ question to Neil:

@Neil I also appreciate the professional tone. I am a skeptic regarding what evolution can actually accomplish. In keeping with your demonstrated patience, I’d be grateful if you would give serious consideration to something that keeps tripping me up. I’ve often thought of natural selection as the heuristic to random mutations’ exhaustive search.

A path-finding algorithm can be aided in finding a path from point A to point B by using distance to B as a heuristic to narrow the search space. Without a heuristic, you are left to blind chance. It is said that evolution has no purpose or goal, so there is no point B. It is also claimed that evolution isn’t simply the result of blind chance, so a heuristic would seem to be required. Somehow, natural selection is supposed to address both of these concerns. Nature selects for fitness, we are told, so somehow we have a heuristic even without a point B.

But what is fitness? How does it work as a heuristic? How is it defined? Evidently, it is all about reproductive success. But how does one measure reproductive success? This is where things get fuzzy for me. Surely evolution is a story about the rise of more and more complex organisms. Isn’t this how the tree of life is laid out? Surely it is the complexity of highly developed organisms that evolution seeks to explain. Surely Mt. Improbable has man near its peak and bacteria near its base. But by what metric is man more successful at reproducing than bacteria? If I am a sponge somewhere between the two extremes, how is a step toward bacteria any less of a point B for me than a step toward man? Why should the fitness heuristic prefer a step upward in complexity toward man in any way whatsoever over a step downward in complexity toward bacteria?

It seems that, under the more obvious metrics for calculating reproductive success, bacteria are hard to beat. Even more, a rise in complexity, if anything, would appear to lead to less reproductive success and not more. So how can natural selection be any sort of heuristic for helping us climb Mt Improbable’s complexity when every simpler organism at the base of the mountain is at least as fit in passing on its genes as the more complex organisms near it’s peak? And without this heuristic, how are we not back to a blind, exhaustive search?