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:One nodal family member Xnr3 lacks mesodermal-inducing activity via activating Smad2/3, but promotes neural induction by antagonizing BMP4 (Hansen et al., 1997; Haramoto et al., 2004).
Category: