The Demon-Haunted World_ Science as a Candle in the Dark - Carl Sagan [133]
The astonishing fact is that similar mathematics applies so well to planets and to clocks. It needn’t have been this way. We didn’t impose it on the Universe. That’s the way the Universe is. If this is reductionism, so be it.
Until the middle twentieth century, there had been a strong belief - among theologians, philosophers and many biologists -that life was not ‘reducible’ to the laws of physics and chemistry, that there was a ‘vital force’, an ‘entelechy’, a tao, a mana that made living things go. It ‘animated’ life. It was impossible to see how mere atoms and molecules could account for the intricacy and elegance, the fitting of form to function, of a living thing. The world’s religions were invoked: God or the gods breathed life, soul-stuff, into inanimate matter. The eighteenth-century chemist Joseph Priestley tried to find the ‘vital force’. He weighed a mouse just before and just after it died. It weighed the same. All such attempts have failed. If there is soul-stuff, evidently it weighs nothing, that is, it is not made of matter.
Nevertheless, even biological materialists entertained reservations; perhaps, if not plant, animal, fungal and microbial souls, some still undiscovered principle of science was needed to understand life. For example, the British physiologist J.S. Haldane (father of J.B.S. Haldane) asked in 1932:
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 influenzas, 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.)
The continuity between atomic physics, molecular chemistry, and that holy of holies, the nature of reproduction and heredity, has now been established. No new principle of science need be invoked. It looks as if there are a small number of simple facts that can be used to understand the enormous intricacy and variety of living things. (Molecular genetics also