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:Furthermore, although unconditional or speedy and persistent helping may be the most effective in providing benefits to vulnerable or needy others, this behavior may have to be tempered by distrustful or punishing tendencies in order to establish stable patterns of reciprocity (Trivers 1971).
Category: