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:Based on these findings, the antagonistic activities between Nodal and BMP signaling are at least in part due to the formation of signaling-inactive Nodal (or Xnr3) -BMP heterodimers (Haramoto et al., 2004; Yeo and Whitman, 2001).
Category: