Today in 1858, Charles Darwin received a manuscript in the mail from the naturalist Alfred Russel Wallace, who was at that time exploring the Malay Archipelago, outlining a theory of evolution. Titled "On the Tendency of Varieties to Depart Indefinitely From the Original Type," but widely known as the Ternate essay for the island Wallace wrote the piece on, the essay was certainly a startle to Darwin, who had been carefully accumulating evidence for a large work on evolution.
In the essay, Wallace describes evolution as the progress, always checked by external circumstances, from an original type:
We believe we have now shown that there is a tendency in nature to the continued progression of certain classes of varieties further and further from the original type--a progression to which there appears no reason to assign any definite limits--and that the same principle which produces this result in a state of nature will also explain why domestic varieties have a tendency to revert to the original type. This progression, by minute steps, in various directions, but always checked and balanced by the necessary conditions, subject to which alone existence can be preserved, may, it is believed, be followed out so as to agree with all the phenomena presented by organized beings, their extinction and succession in past ages, and all the extraordinary modifications of form, instinct, and habits which they exhibit.
Of note in the Ternate essay is Wallace's discussion of the struggle for existence:
The life of wild animals is a struggle for existence. The full exertion of all their faculties and all their energies is required to preserve their own existence and provide for that of their infant offspring. The possibility of procuring food during the least favourable seasons, and of escaping the attacks of their most dangerous enemies, are the primary conditions which determine the existence both of individuals and of entire species. These conditions will also determine the population of a species; and by a careful consideration of all the circumstances we may be enabled to comprehend, and in some degree to explain, what at first sight appears so inexplicable--the excessive abundance of some species, while others closely allied to them are very rare.
I don't know whether Charles Darwin adopted Wallace's language or whether he came to it independently, but Darwin puts great emphasis on the struggle for existence in The Origin of Species, dedicating an entire chapter to the topic. Like Darwin, Wallace correctly emphasizes that the struggle for existence is strongest between similar organisms in similar niches in an ecosystem.
Where the two drastically disagree is in the relationship of domestic animals to the theory of evolution. Whereas Wallace rejects the existence of an analogy between the varieties of domestic animals and the varieties of animals in a state of nature, Darwin cleverly exploits that analogy in the first couple of chapters in The Origin of Species. Indeed, Darwin opens the book with a elucidation of the principles of artificial selection. Only after establishing those principles does he move onto establishing that the struggle for existence can produce similar selective pressures on animals in a state of nature.
Comments