The naruralist whose essay gave Darwin an incentive to publish his own work was?

The naturalist whose essay gave Darwin an incentive to publish his own work was Alfred Russel Wallace.

In 1858, Wallace sent Darwin a manuscript outlining his own theory of evolution by natural selection, which was remarkably similar to Darwin's own ideas. This prompted Darwin to finally publish his own theory, which he had been working on for over 20 years.

The two men's theories were presented together at a meeting of the Linnean Society in London, and both are credited with developing the theory of evolution by natural selection.