Chemistry
Investigating the relationship between olfactory acuity, disgust, and mating strategies
Marjorie Prokosch, Zachary Airington & Damian Murray
Evolution and Human Behavior, forthcoming
Abstract:
Although humans' sense of smell is relatively diminished compared to other species, olfaction is still a central sensory modality through which people evaluate both potential threats and prospective romantic partners. Despite olfaction's role in interpersonal relationships and disease avoidant responses, however, it remains unknown whether variation in olfactory acuity is associated with disease- and mating-relevant psychological constructs and behaviors. In the current exploratory study, we examined the relationships between olfactory acuity, disgust sensitivity, and mating strategies in a sample of undergraduate students (N = 162) at a university in the Southern United States using an extended assessment of olfactory acuity (measuring olfactory threshold, discrimination, and identification). Results revealed that people with greater discrimination acuity were higher in dispositional sexual disgust, but not pathogen or moral disgust. People with greater discrimination acuity were also less inclined towards short-term mating. Further, sexual disgust mediated the relationship between discrimination acuity and short-term mating orientation. These results provide further evidence for the importance of olfaction and olfaction-related disgust in close relationships.
Post-copulatory genetic matchmaking: HLA-dependent effects of cervical mucus on human sperm function
Annalaura Jokiniemi et al.
Proceedings of the Royal Society: Biological Sciences, August 2020
Abstract:
Several studies have demonstrated that women show pre-copulatory mating preferences for human leucocyte antigen (HLA)-dissimilar men. A fascinating, yet unexplored, possibility is that the ultimate mating bias towards HLA-dissimilar partners could occur after copulation, at the gamete level. Here, we explored this possibility by investigating whether the selection towards HLA-dissimilar partners occurs in the cervical mucus. After combining sperm and cervical mucus from multiple males and females (full factorial design), we found that sperm performance (swimming velocity, hyperactivation, and viability) was strongly influenced by the male–female combination. This indicates that sperm fertilization capability may be dependent on the compatibility between cervical mucus (female) and sperm (male). We also found that sperm viability was associated with partners' HLA dissimilarity, indicating that cervical mucus may selectively facilitate later gamete fusion between immunogenetically compatible partners. Together, these results provide novel insights into the female-mediated sperm selection (cryptic female choice) in humans and indicate that processes occurring after copulation may contribute to the mating bias towards HLA-dissimilar partners. Finally, by showing that sperm performance in cervical mucus is influenced by partners' genetic compatibility, the present findings may promote a deeper understanding of infertility.
Gamete-level immunogenetic incompatibility in humans – towards deeper understanding of fertilization and infertility?
Annalaura Jokiniemi et al.
Heredity, forthcoming
Abstract:
Human leukocyte antigen (HLA) immune genes play an important role in partner selection, but it has remained unclear if nonrandom pairing with respect to parental HLA genes could occur at the level of the gametes. We tested this possibility by investigating whether the sperm fertilization competence in humans is dependent on HLA genotype combination of the partners. We conducted a full-factorial experiment, in which the sperm physiological preparation for fertilization among multiple males was studied in the presence of follicular fluid (oocyte surrounding bioactive liquid) of several females. All the studied sperm pre-fertilization physiological parameters (motility, hyperactivation, acrosome reaction, and viability) were strongly dependent on male–female combination. In other words, follicular fluids (women) that induce strong sperm physiological response in some males often induce much weaker response in the other(s). Sperm physiological responses were stronger in HLA-dissimilar male–female pairs than in HLA-similar combinations, but none of the measured sperm traits were associated with genome-wide similarity. Together, these findings shed new light on the evolutionary and immunological mechanisms of fertilization. Furthermore, our results raise an intriguing possibility that against currently prevailing WHO’s definition, infertility may not represent exclusively a pathological condition, but may also result from immunogenetic incompatibility of the gametes.
Exogenous testosterone increases the audience effect in healthy males: Evidence for the social status hypothesis
Yin Wu et al.
Proceedings of the Royal Society: Biological Sciences, July 2020
Abstract:
Several studies have implicated testosterone in the modulation of altruistic behaviours instrumental to advancing social status. Independent studies have also shown that people tend to behave more altruistically when being watched (i.e. audience effect). To date, little is known about whether testosterone could modulate the audience effect. In the current study, we tested the effect of testosterone on altruistic behaviour using a donation task, wherein participants were asked to either accept or reject a monetary transfer to a charity organization accompanying a personal cost either in the presence or absence of an observer. We administered testosterone gel or placebo to healthy young men (n = 140) in a double-blind, placebo-controlled, mixed design. Our results showed that participants were more likely to accept the monetary transfer to the charity when being observed compared to when they completed the task alone. More importantly, this audience effect was amplified among people receiving testosterone versus placebo. Our findings suggest that testosterone administration increases the audience effect and further buttress the social status hypothesis, according to which testosterone promotes status-seeking behaviour in a context-dependent manner.
Elevated recognition accuracy for low-pitched male voices in men with higher threat potential: Further evidence for the retaliation-cost model in humans
Jinguang Zhang et al.
Evolution and Human Behavior, forthcoming
Abstract:
For humans, voice pitch is highly flexible and, when lowered, makes male speakers sound more dominant, intimidating, threatening, and likely to aggress. Importantly, pitch lowering could not have evolved as a threat signal with these effects on signal receivers unless it were honest on average. Drawing on Enquist's retaliation-cost model, we tested the hypothesis that heterosexual men high in threat potential will show enhanced memory for low-pitched male voices when mating motives were activated. Supporting this hypothesis, we found that heterosexual Chinese males higher in trait aggressiveness (Experiment 1) and heterosexual U.S. males higher in upper-body strength (Experiment 2) were more accurate in distinguishing between previously heard and unheard low- but not high-pitched male voices under a mating-motive prime. We believe that this enhanced recognition accuracy for low-pitched male voices facilitates retaliation for men with high threat potential, and thereby serves to probe the honesty of pitch lowering as an aggressive signal.