On the Law Which Has Regulated the Introduction of New Species (Sarawak Law)
In February 1855, Wallace came up with his “Sarawak Law,” summarized these words:
"Every species has come into existence coincident both in space and time with a pre-existing closely allied species."
Published in the “Annals of Natural History” in September 1855, this paper shows Wallace’s biogeographic thinking. He saw space and time as important elements to the existence of species. It also shows that he was on track to uncovering the mechanism behind evolution.
Intrigued by Wallace's paper, Edward Blyth and Charles Lyell, told Charles Darwin about it. Lyell started a “species notebook” for his ideas on evolutionary change. Darwin didn’t understand the Sarawak Law’s significance, yet he heeded Lyell’s advice to publish soon, and began working on his book.
Wallace wrote to Darwin, whom he originally met at the insect-room of the British museum. They exchanged some correspondence relating to Wallace’s “Sarawak Law” and how species diversify.
On the Tendency of Varieties to Depart Indefinitely From the Original Type (Ternate Essay)
In 1858, Wallace wrote his “Ternate essay,” titled, “On the Tendency of Varieties to Depart Indefinitely From the Original Type.” He sent it to Darwin in March 1858.
Darwin was astounded by how similar their ideas were, but did not want to lose credit for his own research. Darwin talked to Lyell and Joseph Hooker. who came up with the solution to present a joint paper at the upcoming Linnaean Society meeting on July 1, 1858. However, they did not secure Wallace’s permission, as he was still collecting in the Malay Archipelago.
Darwin then went on to publish his famous book, 'The Origin of Species' on November 24, 1859.
When Wallace learned of the publication afterwards, he graciously accepted the arrangement.