Darwin: Ancestry In Lyell's Pebbles And Herschel's Words

A lovely passage from the 19th century astronomer John Herschel's  letter to geologist Charles Lyell quoted in Darwin: The Life Of A Tormented Evolutionist:

Words are to the Anthropologist what rolled pebbles are to the Geologist- Battered relics of past ages often containing within them indelible records capable of intelligible interpretation- and  when we see what amounts of change 2000 years has been able to produce  in the languages of Greece & Italy or 1000 in those of Germany, France & Spain we naturally begin to ask how long a period must have lapsed since the Chinese, the Hebrew, the Delaware & the Maleass [from Madagascar] had a point in common with the German & Italian & each other. - Time! Time! Time! - we must not impugn Scripture Chronology,but we must interpret it in accordance with whatever shall appear on fair enquiry to be the truth for there cannot be two truths. And really there  is scope enough: for the lives of the Patriarchs may as reasonably be  extended to 5000 or 50000 years apiece as the days of Creation to as many thousand millions of years.

Besides a great age for earth, a notion which was becoming more accepted as geological observations poured in from Britain and other parts of the world,  in the passage are ideas on ancestry and divergence from a common stock. Herschel's musings on language change influenced Darwin. Were these applicable to life too? Darwin on his return from the Beagle voyage in 1836 was engrossed in geological thinking,  hoping to write a book on South American geology. Charles Lyell encouraged him,  and unlike the cantankerous zoology community, he found the geology fraternity more  approachable and gentlemanly. His paper to the Geological Society on the uplift of the Chilean coast was very well received.

But his zoological samples too were being processed by a variety of experts. Richard Owen found out that the large animal bones Darwin had collected were ancient relatives of living South American sloths and armadillos and not related to European and African mammals. There was, Darwin realized, a genealogical succession of fauna which jarred with the commonly held ideas about separate creation of species.  The ornithologist John Gould pointed out that the seemingly disparate collecting of Galapagos Islands ground dwelling birds with distinctive beaks that Darwin had presented to him and thought of as distinct species of finches, wrens and warblers were in fact a closely related group of finches, with more distant relatives found on the South American mainland. And his collection of mockingbirds which unlike  the finches were correctly labelled according to the islands,  turned out to be 3 related species, each distinct to an island... Ancestry and divergence from a common stock..

John Herschel's "mystery of all mysteries" began tempting him. His long association with dissenting intellectuals and radical thinkers who claimed that life should be explainable by natural laws and his own observations of  nature's bounty and variability had made him  receptive to the idea of species transforming into new species. In this, he departed from his geology mentor Charles Lyell who was a scientist molded in the conservative Anglican tradition. Lyell believed that the dynamics of landscapes and the succession of fauna ultimately revealed the hand of a creator. That humans could have originated via transmutation from an ape was anathema to him. For Darwin, such thoughts held no terror.

Geology was to remain an important part of his work life, but in July 1837 he opened and began scribbling ideas in what is one of the most famous scratchpads in the history of science- Notebook B which he titled Zoonomia (after his grandfather Erasmus Darwin's book), marking a decisive shift in emphasis in his thinking from geology to evolution.