On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection Letter" from Darwin to Asa Gray. This was the first announcement of the Darwin – Wallace theory of evolution by natural selection; the papers appeared in print on 20 August 1858. The presentation of the papers spurred Darwin to write a condensed "abstract" of his "big book" on "Natural Selection". This was published in November 1859 as "On the Origin of Species". On the voyage of the "Beagle" the young Charles Darwin took a break between graduating and starting his career as a clergyman to study the natural history of South America, an interest he had developed at the University
Reactions to On the Origin of Species example and Ramsay's data in chapter 9 of "On the Origin of Species" to estimate that erosion of the Weald's layered dome of Lower Cretaceous rocks “must have required 306,662,400 years; or say three hundred million years“. The "necessary corrections" Darwin made to his drafts for the second edition of the "Origin" were based on comments from others, particularly Lyell, and added a caveat suggesting a faster rate of erosion of the Weald: "perhaps it would be safer to allow two or three inches per century, and this would reduce the number of years to one hundred and fifty or