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:…important role of intragenic and possibly intergenic recombination for the origin of MHC sequence polymorphism is accumulating from population sequence data (Langefors et al. 2001b; Richman et al. 2001, 2003), supporting direct experimental observation using sperm typing (Högstrand and Böhme 1994).
Category: