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:have evolved via mutations targeted around their functional domains while the structural residues are constrained and maintain a highly conserved scaffold (Mackessy 2002; Kini 2004; Fry et al. 2006, 2008; Yamazaki and Morita 2007; Doley et al. 2008).
Category: