Unfragranced body odours of real partners are judged more similar than fake couples; no such difference for fragranced body odour; hormonal contraceptives may influence initial odour-mediated assortment

Evidence for odour-mediated assortative mating in humans: The impact of hormonal contraception and artificial fragrances. CarolineAllen et al. Physiology & Behavior, May 15 2019. https://doi.org/10.1016/j.physbeh.2019.05.002

Highlights
•    Unfragranced body odours of real partners are judged more similar than fake couples.
•    There was no such difference for fragranced body odour samples.
•    Hormonal contraceptives may influence initial odour-mediated assortment.
•    There was a sex difference in favourability of odour similarity within couples.
•    Similarity ratings correlated with some verbal labels described by perfumers.

Abstract

There is substantial evidence for assortative partner preferences in humans based on physical characteristics. In contrast, evidence suggests that olfactory preferences tend to be disassortative, with people preferring body odour of potential partners who are dissimilar at key genetic loci, perhaps to gain fitness advantage through offspring heterozygosity. We compared ratings of perceived body odour similarity of real couples with those of randomly paired ‘fake’ couples. Contrary to prediction, we find that odours of real partners are perceived more, rather than less, similar to each other than fake couples. However, this applied only to natural odour samples: there were no differences in similarity levels of real and fake couples' samples which were collected while wearing artificial fragrances. Furthermore, in light of suggestions that hormonal contraception (HC) disrupts disassortative odour preferences in women, we compared odour similarity among real couples in which the female partner was using or not using HC at the time when the relationship began. We find that odours of HC-using couples are of intermediate similarity between non-using and fake couples, suggesting that HC use during partner choice could affect odour-influenced assortment. We also examined the association between relationship satisfaction and perceived similarity of unfragranced odours of real couples. We found that these are positively correlated in male partners but negatively correlated in the female partners, indicative of a sex difference in the relative favourability of odour similarity in partner preference. Finally, by comparing odour similarity ratings with those given by perfumers using a novel olfactory lexicon we found evidence that similarity judgements were based on the Spicy/Animalic aspects of individual odour profiles. Taken together, our results challenge the conventional view that odour-mediated partner preferences in humans are typically disassortative.