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:…factors such as Hairy, which plays a critical role in the segmentation of the early embryo (Nusslein-Volhard and Wieschaus 1980), Fruitless, which promotes male-specific neural development and behavior (Manoli et al. 2005), as well as Homothorax, a Hox protein co-factor (Ryoo et al. 1999).
Category: