Darwin was influenced by the works of famous scientists such as the astronomer John Herschel (1792-1871) and the naturalist and traveler Alexandr Humboldt (1767-1835).
The latter was responsible, according to Darwin himself, for the impulse to travel to unknown lands on scientific expeditions. The work of geologist and friend Charles lyell (1797 - 1875) also marked Darwin's study. In addition to carrying a copy of the Principles of Geologyby Lyell on his voyage aboard Beagle, Darwin's earliest travel notes were on the subjects of geology.
Darwin also points out the influence of the English vicar's ideas Thomas R. Malthus (1766 - 1834) in the elaboration of the concept of natural selection. In 1798 Malthus suggested that the main cause of human misery was the mismatch between population growth and food production. He said: “The power of the population is infinitely greater than the power of the earth to produce the means of subsistence for man. If the population does not encounter obstacles, it grows according to an arithmetic progression ”.
Malthus did not refer only to human populations, but tried to imagine humanity subjected to the same general laws governing populations of other species of living beings. This was one of the merits of his work, which drew Darwin's attention to the ideas of 'struggle for life' and 'survival of the fittest'.
According to Malthus, while population growth occurs in geometric progression, food production increases in arithmetic progression. That would be one of the explanations for the hunger that plagues much of humanity. These and other conclusions are contained in Population law essay, 1798.
One of Darwin's arguments for selecting the fittest was based on the study of species cultivated by man. At least some cultivated domestic animals and plants were known to belong to the species with representatives still in the wild. Domestic specimens, however, differed in so many characteristics from savages that they could, in general, even be classified as different species.
Darwin devoted himself to the breeding of pigeons, whose domestic varieties were known to originate from a single wild species, the Columba livia, from the selection artificially conducted by the creators. His conclusion was that artificial selection could be compared to that which nature exercised over wild species.
Just as man selects breeders of a particular variety or race, allowing only those who have the desired trait to reproduce, nature selects, in wild species, the individuals most suited to the prevailing conditions. These leave a proportionately larger number of descendants, contributing significantly to the formation of the next generation.
The publication of Darwin's theory
In 1844 Darwin wrote a long paper on the origin of species and natural selection. He did not publish it, however, because he was afraid that his ideas were somewhat revolutionary. Darwin's friends, aware of the seriousness of his work, tried unsuccessfully to persuade him to publish the manuscript before others published similar ideas.
Wallace's select theory
In June 1858, Darwin received a letter from the English naturalist Alfred Russel Wallace (1823 - 1913), which contained conclusions fundamentally similar to his own. Wallace had studied the faunas of the Amazon and East Indies, finding that the species were modified by natural selection. Darwin was amazed at the similarities of Wallace's work in relation to his own, among other things because Wallace was also inspired by the same non-biological source, Malthus's book, Population law essay.
Darwin then wrote a summary of his ideas, which were published together with Wallace's work on July 1, 1858. A year later, Darwin published the complete work in the book. The origin of the species. Darwin's notes confirmed that he conceived his theory of evolution about 15 years before he received Wallace's letter, and he admitted that Darwin had indeed been the pioneer.