Evolution’s Limits – Defining Irreducible Complexity

Mouse Trap

This post is part of a series: Evolution’s Limits



What do mouse traps have to do with testing evolution?  Read on to find out.

I might have figured out how to find the limit of evolution in a lab, and I’m trying to find out if it’s practical.  I’m also using this as an excuse to read up on evolution’s limits.

Before I do anything else, I need to define what I’m talking about – what are the limits of evolution?  Here are the two that I know of:

  • The practical limit of mutation
    • This is the most complex system that can appear one mutation at a time, or at most a few mutations at a time
    • Each step – or nearly every step – has to be such a big improvement that it must give the mutants an unfair advantage in reproduction
  • The practical limit of natural selection
    • This is the smallest effect that an improvement can have, for mutants to reliably out-compete the originals.
    • On the flip side, it’s also the smallest effect that a genetic disease can have, for mutants to reliably be driven extinct by the originals.  A genetic disease that’s not bad enough to eliminate itself by natural selection runs in the family of the person who has it.  For more about this, see the evidence that my simulator is accurate.

In this series, I’ll focus mainly on the first – the practical limit of mutation.  I’ve already covered the other one in some detail.

In this post, I’ll give the definition of the practical limit of mutation, as given by Michael Behe.  He named it irreducible complexity.

He first coined the term in his book Darwin’s Black Box.  He wanted to show that many parts of living things couldn’t have appeared by evolution.  If something is past the practical limit of mutation, he said it’s irreducibly complex.

But how can you tell if something’s past the practical limit of evolution?  He gave a more detailed definition:

“By irreducibly complex, I mean a single system composed of several, well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning”.  (Michael Behe; Darwin’s Black Box; page 39)

This definition makes irreducible complexity easy to test for.  All you have to do is knock out each part, one at a time.  If the machine won’t work without every single one of its parts, it couldn’t have appeared by evolution.  His first example was a mouse trap.  My test – if it proves to be practical – would take a different route: force evolution to go as far as it can until it stops.

I want to make sure that I have a correct, workable definition before building anything on top of it.  His definition is a good start, but it has some pesky corner cases.  I’ll spend at least a couple of posts explaining them.  If needed, I’ll refine his definition to be more relevant to the kind of test I’m thinking of.  I also want to find out all the kinds of mutations that happen, and how common they are.  Finally, I want to do the math on my idea.  If it turns out to be practical, I’ll design the experiment in as much detail as practical, given how little I know about biochemistry and how much time I want to spend on this.

This post is part of a series: Evolution’s Limits



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