The medals have been awarded every 50 years, beginning in 1908. That year marked 50 years after the joint presentation of papers by Charles Darwin and Alfred Russel Wallace. These were "On the Tendency of Species to form Varieties"; and "On the Perpetuation of Varieties and Species by Natural Means of Selection". The papers were both about natural selection as the main cause of evolution. The papers were presented to the Linnean Society of London on 1 July 1858. 