Allomaternal Care in Non-Human Primates

This entry was written by Margot Schneider as part of a project done in BIAN 2133 ‘Human Reproductive Strategies’ at The Australian National University in 2019 Semester 2.


Allomaternal care (AMC), is care provided by someone other than the infant’s mother, occurring at a higher than average frequency in primates than other mammals (Tecot & Baden, 2015). The carer can be relatives, or unrelated individuals, such as other mothers, other males, and young females. These helpers will do anything from nursing the infants, sharing food, or handling the infant (Ross & MacLarnon, 2000). When AMC is provided, it allows the mother more free time, decreasing the inter-birth interval (Heldstab, et al., 2019). Fathers are more likely to provide care when there is paternal certainty, when they do provide care it is steady and is thought to contribute to increased cognitive function. Allonursing is rare, with an extremely high cost, however in certain primate species it is seen to be crucial for a high infant survival rate (Xiang, et al., 2019). However, while AMC is a widespread across the primate order, it is not observed in all species (Ross & MacLarnon, 2000). Understanding the spread of AMC across the primate order can help us determine the selective pressure at play.

Main Text

Reproductive gain

AMC is costly, for it to have evolved it must be beneficial for everyone involved. In primates, it is present in all wide spread radiation events, indicating that there was selective pressure toward it, with nearly 75% of primates exhibiting some level of AMC (Tecot & Baden, 2015). High levels of AMC, lead to increased quality of care, health and survival of the offspring, with increased time for the mother to forage for food. Having helpers look after your young leads to great energetic benefits, with this comes increased fertility. AMC is favoured when there are high levels of energetic stress (Ross & MacLarnon, 2000). Callitrichids (tamarins and marmosets) give birth to twins which is rare among primates, they practice cooperative breeding, living in small social groups with one breeding pair and a lot of help to raise them (Burkart & Van Schaik, 2010). AMC allows the distribution of tasks, reproduction is costly and having an extra set of hands lowers this individual cost (Heldstab, et al., 2019). Tecot and Baden (2015), state that AMC is thought to have developed from two main pathways, either kin selection or reciprocity. Kin selection explains why family members might help, as siblings having children increases your fitness. Reciprocity works because the favour is returned. However, if the task is not reciprocated, it can be costly to the helper. The increased care allows the young to mature earlier, leaving time for the mother to have infants more often, decreasing the inter-birth interval, and increasing her fitness (Ross & MacLarnon, 2000).


Primates are known for their large brains and increased capacity to perform complex tasks, socialise, and form multi-level relationships. Brain tissue however is metabolically expensive, and it is crucial for nutrients to always be available during development (Heldstab, et al., 2019). Therefore, to develop a large brain, consistent high amounts of energy need to be invested, an element of this is allomaternal care, specifically from the father. When paternity is certain, there is an increased likelihood of stable care, which directly correlates to increased brain size. Species which exhibit high levels of allomaternal care (not just paternal care) are also more likely to perform better in socio-cognitive tasks (Burkart & Van Schaik, 2010). This is strongly present in the family callitrichidae, they are more socially tolerant, have better vigilance, and the ability to share food willingly. They possess the ability to inhibit the impulse which tells them to immediately eat food. Fatherly care therefor increases brain development of the infant, and other forms of AMC increase brain development of the adults.


Lactation is energetically demanding, providing this level of care for another individual’s offspring is less frequent then other forms of AMC (Xiang, et al., 2019). A recent study on golden snub nosed monkeys showed that 87% of infants were allonursed by at least one other female than their mother. Golden snub nosed monkeys live in an environment with harsh winters, this can help to explain the development of allonursing. If the infants don’t reach a critical weight before winter there is an increased likelihood of them not surviving. Infant golden snub nosed monkeys require the most milk in the first 3 months of their lives, yet are nursed for more than a year, with a mean inter-birth period of about 2 years. This leads to infants that are raised together wo require varying metabolic demands. Milk production is stimulated by the frequency of nursing, this allows mothers who have older young to provide milk for the newly born infants. Most mothers that share the task of nursing are also related, both kin selection and reciprocity are at play. While the allonursed young had a higher chance of surviving they were also weaned younger, and it is thought to increase both neural development and immune diversity.

Why haven’t all Primates Developed AMC?

While AMC increases fitness, it has not evolved in all primate species. Levels of AMC are often observed in captive primate populations that would otherwise not exhibit this behaviour in the wild (Burkart & Van Schaik, 2010). This indicates that while they possess the ability to allocare, their environment which often determines social structure, is limiting (Ross & MacLarnon, 2000). Orangutans for example are solitary, with no opportunity to develop the social structure required for AMC. AMC is often dictated by stress levels, and increasing brain development, some species of primates may have never had these selection pressures places on them, and therefore had no need to evolve methods of AMC.


AMC in non-human primates is widespread across every radiation event. AMC from family members is thought to be driven by kin selection, whereas when helpers are not related reciprocity is at play. Help ranges from holding the infant, helping to find food, all the way to nursing (the most energetically demanding), the individual providing the care and the type of care matters. Fathers are thought to be the most consistent members of the groups that provide allomaternal care, and their help usually correlates with increased brain development. Other forms of care such as allonursing or more general help result in an increased chance of survival, early weaning, and, for the mother decreased inter-birth interval. Therefore, AMC is evolutionary beneficial increasing the fitness of everyone involved. However, the evolution of AMC is environmentally limited, and not all species have the opportunity or had the pressure to evolve such behaviour.

Literature Cited

Tecot, S. & Baden, A. (2015). Primate Allomaternal Care. Emerging Trends in the Social and Behavioral Sciences, 1-17.

Burkart, J. & Van Schaik, C. (2010). Cognitive consequences of cooperative breeding in primates?. Animal Cognitition, 13, 1-19.

Heldstab, S., Isler, K., Burkart, J. & Van Shaik, C. (2019). Allomaternal care, brains and fertility inmammals: who caresmatters. Behavioural Ecology and Sociobiology, 73(71), 1-13.

Ross, C. & MacLarnon, A. (2000). The evolution of non-maternal care in anthropoid primates: A test of the hypotheses. Folia Primatologica, 71(1), 93-113.

Xiang, Z., Fan, P., Chen, H., Liu, R., Zhang, B., Yang, W., Yao, H., Grueter, C., Garger, P., Li, M. (2019). Routine allomaternal nursing in a free-ranging Old World monkey. Science Advances, 20 February, 5, 1-7.

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