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:However, evidences of CPGs structures have been proposed for human (Duysens and Van de Crommert, 1998; Marder, 2000), initially for locomotion while recent insights suggest that the concept of CPG applies to the upper limb as well (see e.g. Dietz, 2002; Zehr et al., 2004; White et al., 2007).
Category: