‘Irreducible Complexity’ is a phrase coined by Michael Behe in Darwin’s Black Box to describe how some parts of living organisms are too complicated to be put together by Darwinian mechanisms.
Whilst the idea is one I have some sympathy with – there may indeed be biological machinery out there that wasn’t put together by natural selection – the problem is that we just don’t have the data to be able to confidently say one way or the other.
The other problem is that seemingly irreducible systems can, with the steady march of science, suddenly become reducible. Here’s a recent example.
Mitochondria are the boiler room of our cells, providing all the energy. They actually look like discreet cells in themselves, and for good reason. Numerous lines of evidence suggest that they started out as bacteria that became incorporated within the more complicated ‘eukaryotic’ cells. It’s the ultimate in symbiotic relationships where the 2 become 1.
One of the many puzzles that this theory presents is how did the bacterium come to be able to transport across its membrane proteins that previously it would have been keeping out. A group of researchers have identified how this seems to have happened. Having identified strikingly similar proteins in bacteria that are used in the mitochondrial transport machinery they observed:
(i) that protein components found in bacteria are related in sequence to the components of mitochondrial protein transport machines, but (ii) that these bacterial proteins are not found as part of protein transport machines and (iii) that some apparently “primitive” organisms found today have protein transport machines that function with only one or few component parts.
In other words a stepwise process for the co-opting of proteins from one function to another seems to be emerging.
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