We may not have final proof that the cosmos is uniquely
fit for life as it exists on earth – because the possibility of alternative
life forms cannot yet be entirely excluded – but there is no doubt that
science has clearly shown that the cosmos is supremely fit for life as it
exists on earth. For as we have seen, the
existence of life on earth depends on a very large number of astonishingly
precise mutual adaptations in the physical and chemical properties of many of
the key constituents of the cell: the fitness of water for carbon-based
life, the mutual fitness of sunlight and life, the fitness of oxygen and oxidations
as a source of energy for carbon-based life, the fitness of carbon dioxide for the
excretion of the products of carbon oxidation, the fitness of bicarbonate as a
buffer for biological systems, the fitness of the slow hydration of carbon
dioxide, the fitness of the lipid bilayer as the boundary of the cell, the
mutual fitness of DNA and proteins, and the perfect topological fit of the alpha
helix of the protein with the large groove of the DNA. In nearly every case these constituents are the only available candidates
for the biological roles, and each appears superbly tailored to that
particular end. (381)