FROM THE BEAGLE YEARS TO THE LAWS OF LIFE

In March 1837, five months after returning from the Beagle voyage, Darwin settled in London. He was to live in the capital for five years. They were by far his most productive years intellectually. During them, he formulated almost all the main theories later published in the 1850s, 1860s and 1870s: his theory of the origin of species - natural selection; his theory of generation or reproduction and heredity - pangenesis; his theory of the origin of the moral sense in man from ancestral animal social instincts; and his interpretation of the expression of the emotions in man and animals. Of his prominent intellectual productions only two - the theory of sexual selection and the principle of divergence of varieties and species - came later, and they were conceived as elaborations of the theory of natural selection.

In these five London years, two periods were quite exceptionally consequential: the spring and early summer of 1837, immediately after his move to London, and the summer and early autumn of the following year, 1838. At each of these times Darwin made vast escalating moves in his thinking and his theoretical ambitions. By mid- September 1838, indeed, his ambitions had reached a peak never later to be surpassed. One can therefore read the rest of his life as so many sequels to the brainwork of these months.

The work was mostly done in a series of small leatherbound notebooks. In or about July 1837, Darwin opened two notebooks. One, ‘A’ as he labelled it, was devoted to geology; the other, ‘B’, was headed ‘Zoonomia’ and devoted to the laws of life.