Time and space are important concepts for characterizing gene flow in human history. Labels indicate approximate temporal and spatial scales represented by research described in the text. Blue lines illustrate uncertainty about the time of migration, whereas blue boxes represent tighter temporal estimates of gene flow. Red circles represent specific examples of human movement discussed in the text: (a) the expansion of modern humans out of Africa approximately 50,000 years ago (global impact); (b) dispersions following the development of agriculture <10,000 years ago (largely restricted to continental regions); and (c) gene flow driven by intermarriage between adjacent small communities (often recent with only local effects).
Cox and Hammer BMC Biology 2010 8:98 doi:10.1186/1741-7007-8-98