Charles Darwin Writes That He Only Now Realizes the True Span of Time, a Key Element in the Continued Development of His Theory of Evolution by Natural Selection and Major Addition in Subsequent Editions of Origin of Species

An extraordinary and significant letter about the central realizations underlying Darwin’s great theories

 

)n the market for the first time in at least 100 years, it shows his personality, his key realizations, and how he developed some of his own historic theories

 

Formerly in the collection of the great geologist Frederick J. Pack

Darwin more than any other man made us think of the vast span of time on Earth and the various forms of evolution that that span permitted. He had us thinking not in hundreds of thousands of years but in eons of ongoing change. It was not only biological life that changed, but geological formations and the earth where we all live.

Darwin’s interest in geology stemmed from his childhood collection of minerals and his formal study at the University of Edinburgh and Cambridge. He was particularly interested in the idea of Earth changing over long time spans, which influenced his thinking about the possibility of life changing as well. For example, he considered how coral reefs formed, applying his understanding of gradual geological subsidence to formulate a new theory.

Further, his interest in and contributions to geology were significant and influenced his development of the theory of evolution by natural selection. His geological observations, particularly during his voyage on the HMS Beagle, provided evidence for the age of the Earth and the slow, gradual changes in the Earth’s surface. This understanding was crucial for him to grasp the concept of gradual change in living organisms as well. It allowed him to understand the length of time it could take for a species to evolve and also better understand climate change.

In 1868 and 1869, as a prelude to his revised edition of Origin, he engaged in a fascinating and revealing correspondence with James Croll. Croll, who story was a Janitor-to-Scientist saga, was born at Little Whitefield, in Perthshire. After a short time in the village school, he was apprenticed as a wheelwright, but lack of strength compelled him to seek less arduous employment, and he became agent to an insurance company. In 1859 he was appointed janitor in the Andersonian University and Museum, Glasgow. His first contribution to science was published in the Philosophical Magazine for 1861, and this was followed in 1864 by the essay “On the Physical Cause of the Change of Climate during the Glacial Period.” From 1867 to 1881 he held an appointment in the department of the Geological Survey in Edinburgh. In 1876 Croll was elected a Fellow of the Royal Society.

The Darwin Correspondence at Cambridge notes of this and Darwin’s revisions of Origin: “Perhaps the most significant changes though were on the old chestnuts of geographical distribution, and the age of the earth, with the Scottish geologist James Croll entering the roll-call of significant correspondents.” This is the first letter of Darwin to Croll, showing not only his realization about the significance of a span of 1 million years but also showing what he was reading on the subject of Geology as it relates to evolution. Croll published several papers in the “Philosophical Magazine” between 1864 and the date of this letter (1868). The Whittaker he refers to below had published “On Subaerial Denudation,” and “On Cliffs and Escarpments of the Chalk and Lower Tertiary Beds;” Ramsay: “On the Glacial Origin of certain Lakes in Switzerland, the Black Forest, Great Britain, Sweden, North America, and elsewhere;” Jukes: “On the Mode of Formation of some River-Valleys in the South of Ireland.”

In his paper “On Geological Time, and the probable Date of the Glacial and the Upper Miocene Period” (Phil. Mag. Volume XXXV., page 363, 1868) Croll endeavors to convey to the mind some idea of what a million years really is: “Take a narrow strip of paper, an inch broad or more, and 83 feet 4 inches in length, and stretch it along the wall of a large hall, or round the walls of an apartment somewhat over 20 feet square. Recall to memory the days of your boyhood, so as to get some adequate conception of what a period of a hundred years is. Then mark off from one of the ends of the strip one-tenth of an inch. The one-tenth of an inch will then represent a hundred years, and the entire length of the strip a million of years”.

Letter signed, on his letterhead, Down, Kent, September 19, 1868, to James Croll, who had published several papers in the “Philosophical Magazine”, in which Darwin took a keen interest. “I hope that you will allow me to thank you for sending me your papers in the Phil. Magazine. I have never I think in my life been so deeply interested in a geological discussion. I now first begin to see what a million means, and I feel quite ashamed of myself at the silly way in which I have spoken of millions of years. I was formerly a great believer in the power of the sea in denudation, and this was perhaps natural, as most of my geological work was done near sea-coasts and on islands. But it is a consolation to me to reflect that as soon as I read Mr. Whitaker’s paper on the escarpments of England, and Ramsay and Jukes’ papers, I gave up in my own mind the case; but I never fully realized the truth until reading your papers just received. How often I have speculated in vain on the origin of the valleys in the chalk platform round this place, but now all is clear. I thank you cordially for having cleared so much mist from before my eyes. With sincere respect…Charles Darwin.” The wording of this letter also shows us something of Darwin’s personality.

In a follow up letter soon after, with additional questions, Darwin wrote Croll, “I do not ask these questions out of mere curiosity, but I have to prepare a new edition of my Origin of Species, and am anxious to say a few words on this subject on your authority.”

This great letter highlights Darwin’s deep engagement with geological ideas and their implications for his own theories of evolution. The letter further emphasizes Darwin’s growing understanding of geological timescales and how they relate to evolution. He realized that if the Earth could change over vast periods, it was plausible that life could also change over time. This realization was a key element in the development of his theory of evolution by natural selection. It manifests Darwin’s awe of the scale of geological time, and how this new information influenced him. He writes, “I…never fully realized the truth until reading your papers just received”, adding “now first begin to see what a million means.” This realization indicates how the vastness of geological periods sparked a new understanding and appreciation of the timescale needed for evolutionary change, an interpretation confirmed by “The Complete Work of Charles Darwin Online”.

A significant Darwin letter, on the market for the first time in at least 100 years, showing his personality, his key realizations, and how he developed some of his own historic theories.