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:Components of the extracellular signal-regulated kinase (ERK) family of mitogen-activated protein kinases are present in spermatozoa and involved in capacitation (Luconi et al., 1998; de Lamirande and Gagnon, 2002).
Category: