Do “helpers at the nest” increase their parents' reproductive success?

Abstract

"Helpers at the nest," usually offspring of a preceding litter who contribute by feeding the young to increase the reproductive success of a breeding pair, are known in many species of birds and mammals. Although similar behaviors were described by ethnological observations in several human societies, there is a lack of data on their existence and role. This study of 794 reproductive life histories of post-menopausal Berber women of Southern Morocco aims to provide such information. Results show that the presence of "probable helpers" in the household is related to higher fertility scores and is associated with improved survival of offspring to sexual maturity. In contrast to sparse observations from other human societies, there is no indication that child caretaking would be specific to eldest daughters. Although the association between offspring survival and helping patterns seems highly probable, there is no confirmation that child caretaking per se is the relevant variable. Contrary to nonhuman helpers at the nest, workloads of children range from housekeeping to light agricultural tasks, and are not focused on assisting younger siblings. The improvement of reproductive success is probably the result of multiple interactions, among which the network of kinship would play a role at both the levels of economy and reciprocal assistance.

Are elder siblings helpers or competitors? Antagonistic fitness effects of sibling interactions in humans

“…We focused on the number of elder siblings because in humans they are expected to exhibit more cooperative breeding behaviour during childhood [21]. Unlike several previous studies investigating the potential care provided by elder siblings, we considered the effects of all elder siblings and not only those at least 3 years older than their younger siblings [20,41]. This was because we investigated the effects of siblings across the life of the focal individual rather than only during childhood, and because limiting the sample to only those siblings an arbitrary number of years older than the focal individual could bias the sample to laterborn children [21].…”

Maternal effects in cooperative breeders: from hymenopterans to humans

“…Evidence exists to suggest that both pre-reproductive helpers and post-reproductive grandmothers influence breeder reproductive success. For example, pre-reproductive helpers, through reducing the reproductive costs of the mother, can be associated with increased fecundity and/or offspring survival (Hill & Hurtado 1996;Bereczkei 1998;Draper & Hames 2000;Crognier et al 2001;Sear et al 2002). Furthermore, it is known that helping grandmothers can cause helper-mediated maternal effects.…”

Intergenerational conflicts may help explain parental absence effects on reproductive timing: a model of age at first birth in humans

“…In many species of cooperative breeders older siblings help care for young, thus delaying their own dispersal and possibly paying short-term costs in terms of their own reproduction (Jennions & Macdonald, 1994). A similar intergenerational cooperative arrangement has been proposed as a feature of many human societies given the extent of allocare that older siblings provide (Kramer, 2005; Crognier & Baali, 2001). …”