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)