ON THE ORIGINS OF LIFE
It is 1828, a year that encompassed the death of Shaka, the Zulu king, the passage in the United States of the Tariff of Abominations, and the battle of Las Piedras in South America. It is, as well, the year in which the German chemist Friedrich Wöhler announced the synthesis of urea from cyanic acid and ammonia.
Discovered by H.M. Roulle in 1773, urea is the chief constituent of urine. Until 1828, chemists had assumed that urea could be produced only by a living organism. Wöhler provided the most convincing refutation imaginable of this thesis. His synthesis of urea was noteworthy, he observed with some understatement, because “it furnishes an example of the artificial production of an organic, indeed a so-called animal substance, from inorganic materials.”
Wöhler’s work initiated a revolution in chemistry; but it also initiated a revolution in thought. To the extent that living systems are chemical in their nature, it became possible to imagine that they might be chemical in their origin; and if chemical in their origin, then plainly physical in their nature, and hence a part of the universe that can be explained in terms of “the model for what science should be.”*
In a letter written to his friend, Sir Joseph Hooker, several decades after Wöhler’s announcement, Charles Darwin allowed himself to speculate. Invoking “a warm little pond” bubbling up in the dim inaccessible past, Darwin imagined that given “ammonia and phosphoric salts, light, heat, electricity, etc. present,” the spontaneous generation of a “protein compound” might follow, with this compound “ready to undergo still more complex changes” and so begin Darwinian evolution itself.
Time must now be allowed to pass. Shall we say 60 years or so? Working independently, J.B.S. Haldane in England and A.I. Oparin in the Soviet Union published influential studies concerning the origin of life. Before the era of biological evolution, they conjectured, there must have been an era of chemical evolution taking place in something like a pre-biotic soup. A reducing atmosphere prevailed, dominated by methane and ammonia, in which hydrogen atoms, by donating their electrons (and so “reducing” their number), promoted various chemical reactions. Energy was at hand in the form of electrical discharges, and thereafter complex hydrocarbons appeared on the surface of the sea.
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