Carl%20Sagan%20-%20The%20Demon%20Haunted%20World

Newton's Sleep
What intelligible account can the mechanistic theory of life
give of the . . . recovery from disease and injuries? Simply
none at all, except that these phenomena are so complex and
strange that as yet we cannot understand them. It is exactly
the same with the closely related phenomena of reproduction.
We cannot by any stretch of the imagination conceive a
delicate and complex mechanism which is capable, like a
living organism, of reproducing itself indefinitely often.
But only a few decades later and our knowledge of immunology
and molecular biology have enormously clarified these once
impenetrable mysteries.
I remember very well when the molecular structure of DNA
and the nature of the genetic code were first elucidated in the
1950s and 1960s, how biologists who studied whole organisms
accused the new proponents of molecular biology of reductionism.
('They'll never understand even a worm with their DNA.') Of
course reducing everything to a 'vital force' is no less reductionism.
But it is now clear that all life on Earth, every single living
thing, has its genetic information encoded in its nucleic acids and
employs fundamentally the same codebook to implement the
hereditary instructions. We have learned how to read the code.
The same few dozen organic molecules are used over and over
again in biology for the widest variety of functions. Genes bearing
significant responsibility for cystic fibrosis and breast cancer have
been identified. The 1.8 million rungs of the DNA ladder of the
bacterium Haemophilis influenzae, comprising its 1,743 genes,
have been sequenced. The specific function of most of these genes
is beautifully detailed - from the manufacture and folding of
hundreds of complex molecules, to protection against heat and
antibiotics, to increasing the mutation rate, to making identical
copies of the bacterium. Much of the genomes of many other
organisms (including the roundworm Caenorhabditis elegans)
have now been mapped. Molecular biologists are busily recording
the sequence of the three billion nucleotides that specify how to
make a human being. In another decade or two, they'll be done.
(Whether the benefits will ultimately exceed the risks seems by no
means certain.)
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