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:…lifetimes, whereas indirect benefits refer to benefits to genetically related recipients; i.e., benefits that increase the inclusive fitness of benefactors but typicaly imply fitness costs that are not compensated during the benefactors’ lifetimes (Hamilton 1964; Trivers 1971; West et al. 2007).
Category: