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Using Darwin in helping to define the biological essentiality of silicon and aluminium

16 November 2009 Keele University

In this year, 200th anniversary of the birth of Charles Darwin and the 150th anniversary of the publication of ‘On the Origin of Species’ a UK scientist has used Darwin’s seminal work on Natural Selection in helping to define the biological essentiality of the second (silicon) and third (aluminium) most abundant elements of the Earth’s crust.

The lack of any clear or significant biological essentiality for both of these elements is a mystery as all other abundant elements of the Earth’s crust are known to be biologically essential.

Dr Chris Exley, Reader in Bioinorganic Chemistry at Keele University and a world authority on the ways in which aluminium impacts upon life on Earth, says natural selection is often interpreted as ‘survival of the fittest’ but what is often not appreciated is that the selection processes themselves are niche driven, which means that those characteristics which convey fitness in one environment may not convey fitness in another, perhaps adjacent, environment or niche. This is both the strength and the beauty of natural selection and it can be applied to cellular biochemistry as it is applied to speciation of organisms.

Aluminium is biologically reactive, while silicon is biologically inert. Natural selection informs us that the non-essentiality of aluminium is explained by its non-participation in biochemical evolution due to a complete lack of its biologically reactive forms.

On the other hand the biologically available form of silicon (silicic acid) has been extremely abundant throughout biochemical evolution and its biological essentiality has been dictated by its extremely limited biological reactivity.

It is no coincidence that one of the very few reactions of silicic acid is that with aluminium and that this reaction protects against the toxicity of aluminium.

An essential role of silicon throughout biochemical evolution has been to keep aluminium out of life! However, the activities of humans in learning how to extract aluminium from its ores and using it in myriad ways in what is now the Aluminium Age means that Earth’s inherent protection against the toxicity of aluminium is being compromised and that biologically reactive aluminium is now an active participant in biochemical (and hence human) evolution.

Some of the early results of the arrival of biochemically reactive aluminium have been worryingly obvious, including the death of fish and trees in geographical regions impacted by acid deposition, whereas others, and perhaps those which in particular are linked with the human condition, might yet be too subtle to be directly attributable to the participation of biologically-reactive aluminium in the natural selection of the elements of biological essentiality.

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