Given the structural, metabolic, and hereditary demands of living systems--by every unanimous definition of life--nothing found in nature can compete with the combination of organic polymers, aqueous solvent system, oxygen respiration, and nucleic-acid-based molecular coding. Statistically speaking, and from the stark perspective of natural selection acting on a physical domain that always seeks the path of least resistance and greatest efficiency, these solutions will be overwhelmingly selected for by multiple factors across multiple critical dimensions. Relative abundance of raw materials, stability, versatility, potential for complexity, environmental tolerance, efficiency of resource exploitation, and density of information storage and expression all dictate carbon compounds, water, oxygen, and DNA (or an analogous molecular coding system) as the most likely candidates for the synthesis of living organisms. The fact that our planet hosts carbon-based life despite being overwhelmingly rich in silicon and poor in carbon tends to support the hypothesis that organic life possesses an inherent competitive advantage over other potential forms--and on a universal scale, carbon outnumbers silicon by a factor of 10 to 1. Does that mean I'm a "carbon chauvinist"? Maybe. But how exotic do we have to go to get extremely alien results?

Of the hundreds of amino acids available in nature, life on Earth uses only 20 to produce the millions of proteins found in terrestrial organisms. (Twenty is the most that triplicate-nucleotide DNA can code for.) Extraterrestrial life may not only use reverse "mirror-image" amino acid sets, composed of "right-handed" rather than "left-handed" stereoisomers, but may use an entirely DIFFERENT set of amino acids that doesn't overlap with our own in a single instance. It is in billions of years of independent and wholly divergent evolution reflected in alien genes, and their expression in the vastly unpredictable characteristics of proteins fabricated by exotic toolkits of disparate amino acid sets, that we will encounter the truly alien in extraterrestrial life. Life on other worlds will be diverse and strange beyond imagination--even for a carbon chauvinist.

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Pedantic late-night musings--a biased companion piece to ([link]), written from the perspective of carbon chauvinism. I was laying it on pretty thick for maximum outrage and thus quality of response. Whip me, beat me, make me feel cheap--my opinions will probably change by tomorrow anyway.