Allomothering comprises a wide variety of behaviours including: carrying, provisioning, grooming, touching, nursing (allonursing), and protecting infants from predators or conspecifics.
Depending on age-sex composition of groups alloparents, helpers or "handlers" can be non-reproductive males in polyandrous systems, reproductive or non-reproductive adult females, young or older juveniles, or older brothers or sisters helping to raise their younger siblings.
The term allomother first appeared in a sociobiological analysis of reproductive strategies among langur monkeys and referred to group members other than the mother who share care of infants.
However, unrelated adult males have been observed to provide allomaternal care as in fat-tailed lemurs[2] and Barbary macaques.
These species practice facultative cooperative breeding, where a single dominant female reproduces and other group members (fathers, other males and non-reproductive juveniles) provide the majority of care to the infants.
Many studies have shown that cooperative breeding and allomothering provide significant benefits for the development, learning, and socialization of offspring.
[7][8][9] Primates that are cooperative breeders are known for some behavioral elements including territory and group defense, caution, and transferring the offspring between different individuals.
[10] In this relation, some studies have suggested that the potential evolutionary pressures may have formed the behavioral elements and even some morphological traits of infants in cooperative breeding animals.
[10] As it is assumed in comparative studies, cooperative breeding may have led to the evolution of greater cognitive flexibility and problem-solving abilities in infants.
[12][13] It is important to know that these skills may be useful in other social situations rather than raising offspring and the current studies addressing this relationship emphasize further research.
[10] For example, in current comparative research on different species of primates, it is shown that cooperative-breeder species like callitrichids due to their greater social tolerance, and sensitivity to others' signals, may perform better on tasks requiring social learning, communication, and alliance-making than their independently reproducing sister taxa (squirrel monkeys).
[10] In addition, the other important cognitive ability related to sociality and cooperative breeding is prosociality which has been addressed by some research.
Particularly in humans, the characteristics related to shared childcare are thought to contribute to advanced cognitive skills including language, planning, cumulative culture, and intentional teaching.
[20] In Wedge-capped Capuchins, the degree of relatedness best predicts allomaternal interactions, and female siblings are the most likely to act as allomothers to infants.
[21] A number of adaptive functions have been proposed to account for the widespread incidents of allomaternal care in mammalian and avian species.
[4] However, this hypothesis is disputed by evidence such as the observation that in wild Formosan Macaques, nulliparous and multiparous adult females engage in similar rates of allomaternal care.
[6] Other hypotheses include "alliance-formation", where subordinate allomothers endeavour to form social alliances with dominant mothers by interacting with their infants.
[21] However, this hypothesis would not explain the high levels of allocare seen by juvenile, subadult or unrelated adult males in many [primate] species.
[20] Infants may also benefit from their mother's more effective feeding and allomaternal care through a faster maturation and growth rate or earlier weaning time (at a younger age but not at a lower weight).
[26] Notably, at least cercopithecine females are extremely interested in infants, so allomaternal care seems to be limited due to restriction by mothers.
This non-strict female hierarchy appears to have enhanced the benefits and reduced the costs of allomaternal care which allowed for the evolution of allomothering in colobine species.
[23] By contrast, cercopithecine species are generally omnivorous and engage in high levels of within group contest competition for food, which is hypothesized to have influenced the formation of strict female dominance hierarchies.
[24] This strict female hierarchy appears to have reduced the benefits and increased the costs of allomaternal care, which may explain the low rates of allomothering observed in most cercopithecine species.
However, research by Bădescu, Watts, Katzenberg, and Sellen on wild chimpanzees at Ngogo, Uganda observed allomothering with some individuals.