Final answer:
Charles Darwin and Alfred Russel Wallace independently discovered natural selection, presenting their findings in 1858 before the Linnean Society and leading to Darwin's seminal work, 'On the Origin of Species.
Step-by-step explanation:
The two people who independently discovered the concept of natural selection were Charles Darwin and Alfred Russel Wallace. Their significant contributions to evolutionary biology came in the mid-nineteenth century after extensive observations during their individual expeditions to various tropical locations around the world. Darwin's trip aboard the H.M.S. Beagle and Wallace's explorations in Brazil and the Malay Archipelago led to the formulation of ideas concerning species adaptation and variation. Both naturalists presented their scientific papers on natural selection to the Linnean Society in 1858.
Darwin observed the variety among ground finches in the Galápagos Islands, noting the gradation of beak sizes and shapes, which provided evidence supporting his idea of species modification from common ancestors. Similarly, Wallace made parallel observations that solidified the theory of natural selection, a process by which traits beneficial for survival in changing environments become more common over generations. This culminated in a shift within populations—a process Darwin referred to as "descent with modification." A year after their joint presentation, Darwin published 'On the Origin of Species,' providing detailed arguments for evolution by natural selection.