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:The identification of a single chicken 50-RACE product contrasts with our previous identification of four different noncoding exons by 50 RACE of human and mouse transcripts (Drews et al. 2005), and suggests that mammalian exon 1c represents the ancestral exon.
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