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A striking example of the exchange of grooming against a social favour is the so-called 'baby market': the fewer infants in a group the higher the price that has to be paid in the form of grooming to gain the mother's permission to inspect and handle it. This was first described for chacma baboons, but similar results have been found in other primate species, such as sooty mangabeys and vervet monkeys (Fruteau et al. 2011), longtailed macaques (Gumert 2007), spider monkeys (Schaffner & Aureli 2005; Slater et al. 2007) and golden-snub nosed monkeys (Wei et al 2013). The latter is a highly interesting example of baby markets in a harem-species.
One should not expect baby markets to operate in all species, for example not in non-seasonal breeders in which fluctuations in numbers of small infants are generally low and also not in species that lack steep dominance hierarchies and in which mothers are permissive towards other females eager to handle their infants. The latter can notably be expected in groups with high degrees of kinship among the adult females. A good example can be found in Caselli et al (2021).
Negotiating the price of access to an infant
The video shows members of our captive group of vervet monkeys held in the Primate Center of Strasbourg (France).
Two females groom a mother holding her infant. The groomers once in a while attempt to grab the infant, but the mother does not allow this as long as she reckons she can refuse and demand more grooming
(video by Yann Gobrecht)
Baby-grooming vervet (small).mp4Caselli, M., Zanoli, A., Palagi, E. & Norscia, I. (2021). Infant handling increases grooming towards mothers in wild geladas (Theropithecus gelada). Behavioural Processes, 104501
Fruteau, C., van de Waal, E., van Damme, E. & Noë, R. 2011. Infant access and handling in sooty mangabeys and vervet monkeys. Animal Behaviour, 81, 153-161 pdf
Gumert, M. 2007. Grooming and infant handling interchange in Macaca fascicularis: the relationship between infant supply and grooming payment. International Journal of Primatology, 28, 1059-1074
Henzi, S. P. & Barrett, L. 2002. Infants as a commodity in a baboon market. Animal Behaviour, 63, 915-921.
Schaffner, C. & Aureli, F. 2005. Embraces and grooming in captive spider monkeys. International Journal of Primatology, 26, 1093-1106.
Slater, K. Y., Schaffner, C. M. & Aureli, F. 2007. Embraces for infant handling in spider monkeys: evidence for a biological market? Animal Behaviour, 74, 455-461.
Tiddi, B., F. Aureli, et al. 2010. Grooming for infant handling in tufted capuchin monkeys: a reappraisal of the primate infant market. Animal Behaviour, 79: 1115-1123
Wei, W., Qi, X., Garber, P. A., Guo, S., Zhang, P. & Li, B. 2013. Supply and demand determine the market value of access to infants in the Golden Snub-Nosed monkey (Rhinopithecus roxellana). PLoS ONE, 8, e65962.
last update: 29 SEP 2021
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