Darwin subsequently sent Wallace's manuscript to Lyell; with his own covering letter of 18th June 1858 that included the following sentences:- My dear Lyell, Some year or so ago, you recommended me to read a paper by Wallace in the Annals, which had interested you & as I was writing to him, I knew this would please him much, so I told him.
He has to day sent me the enclosed & asked me to forward it to you. Your words have come true with a vengeance that I shd. You said this when I explained to you here very briefly my views of "Natural Selection" depending on the Struggle for existence. If Wallace had my manuscript sketch written out in 1842 he could not have made a better short abstract! Please return me the manuscript which he does not say he wishes me to publish; but I shall of course at once write & offer to send to any Journal.
He, like Darwin years earlier, had been struck by a viewpoint attributable to Thomas Malthus, which held that populations will tend to outstrip the food supply naturally available to them.
In a covering letter Wallace asked that Darwin forward the memoir to a famous scientist named Sir Charles Lyell, if Darwin thought the content merited Lyell's attention.
Wallace had concluded that species throw up occasional variations in form which may decisively benefit the individuals who carry that variation.
As early as July 1837 Darwin opened a notebook to record his thoughts on "that mystery of mysteries - the origin of species" as this entry from his diary relates:- The direction of the development of Darwin's thoughts can perhaps be illustrated by this famous Tree of Life sketch from his Notebook B dating from 1837-8:- Charles Darwin's early evolutionary theory insight of how a branching tree-like genus of related species might originate by divergence from a starting point (1) to effectively establish related species at such notional points as A, B, C and D.
There is an accompanying text annotation that reads:- I think Case must be that one generation then should be as many living as now.
Heaven forfend me from Lamarck nonsense of a "tendency to progression" "adaptations from the slow willing of animals" &c, - but the conclusions I am led to are not widely different from his - though the means of change are wholly so - I think I have found out (here's presumption!
) the simple way by which species become exquisitely adapted to various ends.
Whilst at Cambridge his interest in Natural History led to informal contacts with professors of Botany and Geology and, through these contacts, to an invitation to join HMS Beagle on an exploratory voyage to South America and beyond as a geologist.
This invitation arrived just as Darwin had completed his university degree course and effectively postponed his actually becoming ordained as a clergyman.
So all my originality, whatever it may amount to, will be smashed.
Though my Book, if it will ever have any value, will not be deteriorated; as all the labour consists in the application of the theory.
I hope you will approve of Wallace's sketch, that I may tell him what you say.