Previously awarded to commemorate the 50th,100th and 150th anniversaries of the reading of the joint paper by Charles Darwin and Alfred Russel Wallace "On the Tendency of Species to form Varieties; and the Perpetuation of Varieties and Species by Natural Means of Selection", which was read on 1 July 1858, and published by the Linnean Society. In recognition of the continuing importance of research on evolutionary biology, the Council of the Society announced in 2008 that the medal would be awarded annually from 2010.
Source: The Linnean Society of London - The Dawin-Wallace Medal