Editing Modern synthesis (20th century) (section)

===Hamilton's inclusive fitness, 1964===
{{further|Inclusive fitness|Kin selection}}

In 1964, [[W. D. Hamilton]] published two papers on "The Genetical Evolution of Social Behaviour". These defined [[inclusive fitness]] as the number of offspring equivalents an individual rears, rescues or otherwise supports through its behaviour. This was contrasted with personal reproductive fitness, the number of offspring that the individual directly begets. Hamilton, and others such as [[John Maynard Smith]], argued that a gene's success consisted in maximising the number of copies of itself, either by begetting them or by indirectly encouraging begetting by related individuals who shared the gene, the theory of [[kin selection]].<ref name=Hamilton/><ref>{{cite journal |last=Maynard Smith |first=John |author-link=John Maynard Smith |year=1964 |title=Group Selection and Kin Selection |journal=[[Nature (journal)|Nature]] |volume=201 |issue=4924 |pages=1145–1147 |doi=10.1038/2011145a0|bibcode=1964Natur.201.1145S |s2cid=4177102 }}</ref>