Cross-modal associations of human body odour attractiveness with facial and vocal attractiveness provide little support for the backup signals hypothesis: A systematic review and meta-analysis

Assessing the attractiveness of potential mating partners typically involves multiple sensory modalities, including the integration of olfactory, visual, and auditory cues. However, predictions diverge on how the individual modalities should relate to each other. According to the backup signals hypothesis, multimodal cues provide redundant information, whereas the multiple messages hypothesis suggests that different modalities provide independent and distinct information about an individual's mating-related quality. The backup signals hypothesis predicts a positive association between assessments based on different modalities, whereas no substantial correlation across modalities is expected under the multiple messageshypothesis. Previous studies testing the two hypotheses have provided mixed results, and a systematic evaluation is currently missing. We performed a systematic review and a meta-analysis of published and unpublished studies to examine the congruence in assessments between human body odour and facial attractiveness, and between body odour and vocal attractiveness. We found positive but weak associations between ratings of body odours and faces (r = 0.1, k = 25), and between body odours and voices (r = 0.1, k = 9). No sex differences were observed in the magnitude of effects. Compared to judgments of facial and vocal attractiveness, our results suggest that assessment of body odour provides independent and non-redundant information about human mating-related quality. Our findings thus provide little support for the backup signals hypothesis and may be better explained by the multiple messages hypothesis