Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:They posited that trans acting differences tend to generate intra-
specific expression polymorphisms (Lemos et al. 2008, Wittkopp et al. 2008, Emerson et al. 2010) that might in turn be fixed by drift (Coolon et al. 2014).
Category: