As an article at Wired reminds us, it was on July 1, 1858, that the theory of evolution by means of natural selection got its first public presentation, at a meeting of the Linnean Society in London. The paper† read to the society was a composite that included work by both Charles Darwin and Alfred Russel Wallace.
Darwin had been working on developing and explaining his theory during the roughly twenty years that had passed since his voyage on HMS Beagle. He anticipated (correctly) that the theory would meet with considerable resistance, and had therefore planned an extensive, multi-volume work to present it. Wallace was a young English naturalist, working in Malaysia, who wrote to Darwin in June, 1858, enclosing a short paper in which he outlined essentially the same theory as Darwin’s. In his letter, Wallace asked Darwin to read the paper, and to forward it for publication if it was good enough.
Darwin wrote to the geologist Charles Lyell and the botanist Joseph Hooker, to whom he had previously shown some of his early work; Lyell had also been suggested by Wallace. Lyell and Hooker arranged for the composite paper to be presented to the Linnean Society, with their own letter of introduction explaining the circumstances of the parallel development. The initial reaction to the paper was rather subdued, but it was published in the Society’s Proceedings later that year.
As both Darwin and Wallace acknowledged, although they could explain how natural selection would drive evolution, and how heritable traits that led to differences in reproductive success might become common in a population, they could not explain how traits were inherited in the first place. It took the later development of work in genetics by Gregor Mendel to begin an explanation, an explanation that was still sketchy until the discovery of DNA in the mid-20th century. Both Darwin and Wallace also acknowledged the influence of the essay Population, by Thomas Malthus, published in 1798.
Malthus observed that population was held in check because not every individual would survive to reproduce. As Wallace wrote, “It suddenly flashed upon me … in every generation the inferior would inevitably be killed off and the superior would remain — that is, the fittest would survive.”
Darwin would go on to publish the celebrated summary of his work, On the Origin of Species by Means of Natural Selection, in 1859. Biology would never be the same.
† The link to the Linnean Society site, for the original 1858 presentation, appears to be broken. However, the Wiley Online Library has a downloadable copy here.