Five family members from the GabT-like protein family. The first three are very similar. These enzymes are considered by current standards to be homologous, that is, evolutionarily derived.
The five enzymes shown above are clearly related in structure, especially the three on the left. Yet none of the others can replace BioF2’s function in the cell, even when mutated and made in large amounts. Why is that? Probably because each enzyme is a structural whole, whose sequence is made to work together as a whole. Substituting or changing little bits doesn’t work.
Here are the concluding paragraphs of our recent paper where we explain the problem and propose a new way of thinking about it:
“Although there is as yet no satisfactory theory of biology to take the place of Darwinism, we believe the time has come for serious pursuit of such a theory. To quote one of our previous papers :
The insights we gain from the critique of neo-Darwinism can and should inform the construction of a new theory to take its place. That is, in pinpointing the key problems with the old theory we are identifying crucial respects in which its replacement must differ from it. We ourselves have become convinced that intelligent causation is essential as a starting point for any successful theory of biological innovation. If this is so, what is needed now is an elaboration of the general principles by which living things have been designed.
To that end, one of our inferred principles of design is this :
The substantial reworking of a homologous structure needed to give it a genuinely new function is more suggestive of reapplication of a concept than adjustment of a physical thing.
And another is this : … More. (Reeves MA, Gauger AK, Axe DD (2014) Enzyme families—Shared evolutionary history or shared design? A study of the GABA-aminotransferase family. BIO-Complexity 2014 (4):1-16. doi:10.5048/BIO-C.2014.4.)
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