Olfaction in the engagement and development of adaptive reciprocity in human infants and parents
Professor Benoist Schaal, Centre for Smell, Taste and Food Science, CNRS, Dijon, France
What are the roles of olfaction in the early formation of human infants’ cognition about parents and in promoting parents’ recognition of, and attachment to, infants? On the infants’ side, olfaction sets on in utero. Prenatally-acquired odour memories persist postnatally and modulate selective responses in infants. In parallel to this transnatal odour continuity, mothers convey evolved mammary chemosignals that further boost the vital ingestion of colostrum. In the same time, the mammary niche shapes immediate/deferred olfactory cognitions related to social and biotic (food) items. In addition to arousal regulation and orientation, infant perception of mother’s odour engages then visual cognition of her and others, initiating multisensory social intelligence. On the other side, parents appraise infants’ body odours from birth, perhaps before, leading to the rewarding awareness of their individuality. Later, infant odours are involved in many aspects of adaptive responses underlying the economy of mother-infant exchanges of matters (lactation) and commodities (solace, hygienic care). These include attention, discrimination, recognition, monitoring of infant odour changes, with ensuing engagement of empathetic feelings and onset/maintenance of lactational physiology. Olfaction appears thus significant in turning on, sustaining and, in some cases, disturbing the loop of early mother-infant reciprocity effected in emotion and knowledge, and in behaviour and physiology.
Olfaction as a moderator of parent-child bonding: new insights on the base of a HLA genotyped family cohort
Dr Ilona Croy, University of Dresden Medical School, Germany
Human parent-child bonding and kin recognition are modulated by olfactory stimuli. This modulation seems age depended: while humans are much in favour of their newborns’ body odour, the enthusiasm seemingly decreases when the children get pubertal. Additionally, studies about mate choice suggest, that humans prefer the smell of an opposite sex partner who differs in terms of genetic HLA profile. The group aimed to integrate those concepts by examining preferences of mother for the body odour of the own, HLA-similar and -dissimilar children over the whole period of childhood and adolescence. In a cross-sectional design, a total of 164 mothers were presented to probes of their own and four other children, aged 0 to 18 years. HLA profiling [HLA A, B, C, DR, DP, DQ] was performed for mothers and children and the estrogen and testosterone concentration was determined for all pre- to postpubertal children. Mothers preferred odours of their own offspring compared to other children for all age groups, except during puberty. During this time, body odour identification ability dropped as well. An interaction showed a negative correlation between maternal pleasantness rating and donors testosterone concentration for the own son and a positive correlation for other boys. HLA similarity had no major impact on the maternal assessment of probes. The data suggests that familiarity, and not genetic similarity, drives body odour preference. In the light of clinical studies, the group assumes that infantile body odour preference is a learned mechanism which is driven by positive parenting experiences.
Olfaction, MHC and mate choice
Dr Jan Havlíček, Charles University, Czech Republic
Major histocompatibility complex (MHC) is a key part of adaptive immune system functioning. There is ample of evidence across various vertebrates indicating preferences for odour of MHC-dissimilar and diverse partners. However, the results of human studies are rather mixed. The current meta-analyses found no systematic preference for MHC-dissimilar partners. Further, there was no effect of hormonal contraception as reported in some early studies. In contrast, there was a moderate but systematic preference for MHC heterozygous partners. Although, MHC similarity may have limited effect on mate choice several studies show that it negatively affects sexual satisfaction. Finally, it was shown that couples sharing high number of MHC alleles are frequently having problems to conceive. The main drawback of majority of available data is that they are based on genetically highly heterogenous populations mainly from Europe and Northern America. Future studies should thus focus on MHC-related mate choice in more homogenous small-scale societies controlling for number of potentially confounding factors such as background genetic make-up.
Individual differences in emission and perception of human body odours
Dr Camille Ferdenzi, Lyon Neuroscience Research Centre, CNRS, France
The sense of smell, which has long been underestimated in humans, is now recognised as being particularly sharp in a broad diversity of contexts. One of the main functions of olfaction in numerous species is social communication. In humans, there is evidence that odours – especially those conveyed by the body – are extremely important in interpersonal relationships. However, many aspects of social communication remain to be explored to fully understand this function in humans. This presentation will focus on within- and between-individual variations in production and perception of odours conveyed by the body (endogenous but also exogenous odours). Current knowledge and new data will be presented regarding differences according to sex, culture, intergroup relations, hormonal status and emotional state. In particular, results involving underexplored categories of compounds (acidic fraction of body odour) and little-known odour sources (other than the axilla) will be put forward. Finally, this presentation will discuss how understanding variations can contribute to elucidate the social function of odours, and will point to current methodological challenges in the field. Propositions will be made for possible directions to take in future research.