Biology fine-tuning

One suspects that the lack of contemporary interest in Henderson s work might have been because such ideas were closely associated with the teleological design arguments of the past, which had been discredited by the emergence of natural selection as a better explanation for biological fine-tuning and, to a far lesser extent, by the philosophical objections of Hume (1779) [19] and Kant (c. 1790) [20]. 

The unique suitability of iron comes from the extreme variability of the Fe2+/Fe3+ redox potential, which can be fine tuned by well-chosen ligands, so that iron sites can encompass almost the entire biologically significant range of redox potentials, from about —0.5 V to about +0.6 V. 

Although exhaustive efforts have been made in the search for biologically acceptable catalysts, there are only a few examples of low toxicity, which mainly lead to atactic polymers of little practical use. Another route to gain control over the tacticity of PHB is the transformation of cheap building blocks to enantiomericaUy pure p-BL, which can be distilled off from the catalyst and polymerized with retention of the stereochemistry by ecofriendly initiators. This route combines many advantages. At first, even toxic metal centers can be chosen since the product can easily be separated from the catalyst and secondly, any tacticity of the polymer will be available by simply mixing enantiopure p-BL with the racemic mixture in the desired ratio. In this manner a fine-tuning of the mechanical properties becomes possible and easily performable (Fig. 36). 

These ideas may be translated to natural product diversity. Ecosystems of greater natural product diversity are expected to be more robust (which, by analogy, may be termed natural product redundancy). Under conditions of high diversity, a semiochemical that disappears may be replaced by another one, in a fine tuning of the ecosystem. In contrast, compensation in an ecosystem of scarce natural product diversity needs drastic changes. Thus, the diversity of natural products may be taken as a measure of the contribution to biological evolution. 

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