 As the discussion of evolutionary individuals in  section 3  indicated, responses to the question of whether natural selection has created groups that are themselves biological individuals has been important to the history of the Focal Question. Groups here might range from temporary dyads of individuals, such as two crickets sharing a ride on a leaf (Sober &amp; Wilson 1998), through to higher-level taxonomic groups whose members are largely separated in space and time, such as planktotrophic mollusks (Jablonski 1986, 1987). One fundamental distinction that emerged with the revival of group selection, largely through the work of David Sloan Wilson (1975, 1977, 1980, 1983) and Elliott Sober (D.S. Wilson &amp; Sober 1989; Sober &amp; Wilson 1994, 1998), is between two sorts of groups: superorganisms and trait groups.