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What are the benefits of having a village? Effects of allomaternal care on communicative skills in early infancy

https://doi.org/10.1016/j.infbeh.2019.101361Get rights and content

Highlights

  • Attending formal childcare does not impact communicative behaviors during infancy.

  • More exposure to Household AMC is predictive of higher rates of spontaneous giving.

  • More exposure to Household AMC is predictive of lower rates of turn taking.

  • Number of siblings present significantly impacts several communicative behaviors.

  • Naturalistic follows of infant interactions with caregivers and siblings are needed.

Abstract

This study investigates whether exposure to allomaternal care (AMC—care for infants from individuals other than the mother) improves rates of communicative behaviors during late infancy by providing more opportunities to practice communicating with varied caregivers. Data were collected from 102 typically-developing infants aged 13–18 months and their mothers. AMC variables were collected using a current care questionnaire, structured 14-day diary, and longitudinal interview. Communicative behaviors were assessed through post hoc microcoding of in-lab administrations of the Early Social Communication Scales (ESCS), as well as additional microcoding of the Bayley III Screening Cognitive Subtest. Demographic covariates were also included. For each communicative behavior, backward model selection was used to determine the best fitting linear regression model. Results suggested that rates of turn-taking decreased with Household AMC (p < 0.008), but increased with two or more siblings present at home (p < 0.01). Conversely, rates of spontaneous giving increased with Household AMC (p < 0.003) regardless of the presence of siblings. Notably, exposure to more AMC was neither helpful nor harmful for many of the tested communicative behaviors, although the number of siblings present was significantly related to rates of following commands, as well as pointing and reaching. Ultimately, this study suggests that household level experiences with AMC, rather than formalized care, impact the development of some communicative behaviors during late infancy.

Introduction

During the late stages of infancy prior to toddlerhood, typically developing infants undergo developmental changes in both their language abilities and their energetic requirements. Before the age of two, typically developing infants are not yet considered highly competent communicators because they cannot yet string together words in such a way as to produce meaningful speech (Kuhl & Meltzoff, 1996). However, during this time, infants practice babbling, increase their vocabulary to a small range of words (Kuhl & Meltzoff, 1996; Oller et al., 2013), and develop the ability to share joint attention on subjects of interest (Tomasello & Rakoczy, 2003). Infants also experience energetic changes during this time, such that brain energy needs increase, fat deposits to support those needs begin to decrease, and mother’s milk alone no longer provides enough caloric support to meet these increasing energetic needs (Dettwyler, 1995; Humphrey, 2010; Kuzawa, 1998; Kuzawa et al., 2014). In humans, the dependency period is particularly prolonged to compensate for these issues (Aiello & Wells, 2002; Kuzawa et al., 2014; Leigh, 2012), and provide more time for the infant to be exposed to signal-rich experiences that appropriately shape brain development to support optimal conditioning to the cultural environment (DeVries, 1999; Greenough, Black, & Wallace, 1987; Hertzman & Boyce, 2010; Kolb, Mychasiuk, & Gibb, 2014). Allomaternal care (AMC, or supplemental care from individuals other than the mother) may be a key mechanism that supports optimal brain development during late infancy.

Notably, humans are unique in their universal expression of extensive cooperative care for infants via AMC, a trait that likely evolved relatively early on within the Homo lineage (e.g., Burkart, Hrdy, & van Schaik, 2009; Hawkes, 2014; Hrdy, 2007, 2009; Isler & van Schaik, 2012; Meehan, 2014; Meehan & Crittenden, 2016). AMC can come in the form of food sharing between allomaternal caregivers and infants, which can improve physical growth outcomes for infants by supplementing their energetic needs (Burkart et al., 2014; Isler & van Schaik, 2012, 2014), and historically researchers have focused efforts on exploring this benefit as physical growth and instances of food sharing are relatively easily measured. In fact, cooperative care through AMC and collaborative foraging (which enables food sharing) may have coevolved such that they produced similar selective pressures on the ontogeny of communicative behaviors associated with cooperation in both adults and infants (Tomasello & Gonzalez-Cabrera, 2017). Thus, AMC may also provide important developmental benefits for infant communicative abilities in addition to offsetting energetic needs, an outcome that has not yet been assessed. The current study seeks to understand how differences in exposure to AMC impact developmental outcomes within late infancy, providing a new avenue for understanding why humans continue to exhibit such extensive AMC across cultures.

Importantly, AMC can come in a variety of forms, including care from related and unrelated individuals, within both formal and informal settings. While care received in formal settings, such as childcare facilities and preschools, has been studied fairly intensively, care received in informal settings has received much less attention despite its high degree of prevalence across cultures (but see; Geoffroy et al., 2010; Hansen & Hawkes, 2009; Leach et al., 2008; NICHD Early Child Care Research Network, 2001). Particularly in non-Western cultures, but also in the West, AMC is frequently conducted by grandmothers and older siblings (e.g., Kramer & Veile, 2018; Sear, 2016). Grandparents have received attention for their ability to enable parents (mothers in particular) to get back to engaging in the workforce by providing free childcare in the home (e.g., Brady, 2016; Wheelock & Jones, 2002), with less focus on the potential developmental benefits the infant might receive from interacting with grandparents. Additionally, while older siblings are generally less recognized as caregivers in the United States, evolutionarily and in non-Western contexts, older siblings have played a very important role in providing significant levels of AMC (e.g., Kramer & Otárola-Castillo, 2015; Kramer & Veile, 2018), although the types of care and language input they use to communicate with infants may vary significantly from those provided by older individuals (e.g., Hoff, 2006). More research is needed to determine what ways informal care of all types might impact developmental outcomes by providing additional opportunities for language exposure.

If AMC does indeed help improve an infant’s communicative skills early on, this would not only translate to improvement in abilities to solicit care during early childhood (potentially improving survival outcomes), but also increased time to practice and perfect collaborative communicative skills for use in cooperative behaviors in later adulthood (potentially improving mate attraction and thus reproductive outcomes) (Tomasello & Gonzalez-Cabrera, 2017). Skills like shared attention and turn-taking are highly involved in cooperative activities, impacting a child’s ability to recruit attention and help from adults (i.e., solicit caregiving), as well as an adult’s abilities to coordinate social activities like recruiting help from other adults to share in the burden of care or participate in collaborative foraging (see Tomasello & Gonzalez-Cabrera, 2017). From the infant’s perspective, exposure to more AMC equates to exposure to more prospective communicative partners, potentially enhancing opportunities for infants to practice their skills of attracting attention and communicating needs to others (Aiello & Wells, 2002; Hawkes, 2014; Hrdy, 2007; Kolb et al., 2014; Nelson & Bloom, 1997).

In general, when infants interact with older children and adults, they have opportunities to learn and practice culturally-appropriate ways of communicating, and develop basic conversational skills like turn-taking and sharing attention (Bahrick & Lickliter, 2012; Feldman, Bamberger, & Kanat-Maymon, 2013; Greenough et al., 1987; Hedenbro & Rydelius, 2014; Hoff, 2006; Lewkowicz, 2012; Tomasello & Rakoczy, 2003). Since different types of caregivers are generally culturally-primed to interact with infants in distinct ways (Beebe & Steele, 2013; DiCarlo, Onwujuba, & Baumgartner, 2014; Fouts & Lamb, 2009; Jung & Fouts, 2011), different caregivers may also expose infants to slightly different communicative strategies. Previous research suggests that while joint actions and gestures such as pointing, showing, placing, and offering are universally expressed (regardless of culture) by children when interacting with adults at a young age (appearing between 8–15 months of age), the social environment helps determine the frequency and timing with which infants use these signals with caregivers (Salomo & Liszkowski, 2013). Generally speaking, between 12–18 months, children engage in a lot of joint attention behaviors, working to perfect behaviors like making eye-contact, alternating gaze, and pointing (Bakeman & Adamson, 1984; Carpenter, Nagell, & Tomasello, 1998; Tomasello, 1995). While most children have started to develop a small vocabulary of words by 15 months, generally only after 18 months do children become increasingly reliant on verbal communication (Bakeman & Adamson, 1984; Carpenter et al., 1998; Tomasello, 1995). Heightened AMC could be viewed as creating a specific type of social environment which provides opportunities for infants to gain increased exposure to culturally appropriate use of gestural (and verbal) communicative skills by increasing the number of potential signalers with which the infant can practice these skills.

Therefore, AMC potentially increases exposure to more varied stimuli and sensory experiences, which enables the brain to develop neural pathways that allow the infant to better perceive, categorize, and respond to signals in a culturally-appropriate way (Kolb et al., 2014; Nelson & Bloom, 1997; Singer, 1995; Sterner et al., 2012). The current study seeks to illuminate whether there are measurable differences in infant use of communicative behaviors as predicted by exposure to AMC, such that infants exposed to more AMC utilize communicative behaviors at a higher frequency to generate shared attention during dyadic interactions. In addition to AMC measures, this study emphasizes the possible impact siblings might have on infant development, utilizing birth order as a measure of the number of sub-adult communicators present in the home that could play an important role in helping infants develop certain behaviors.

Section snippets

Overview

This study was approved by the University’s Institutional Review Board for Research Involving Human Subjects, and was conducted in accordance with APA ethical standards in the treatment of the study sample. Mothers and their typically developing infants were recruited to participate in this study between May 2017 and October 2018 in Tucson, Arizona. Following screening and informed consent, mothers responded to online questionnaires through Qualtrics (a secure software program) to provide

Results

Across the twelve communicative behaviors assessed using linear regression of null models followed by backward model selection, two outcomes were significantly predicted by Household AMC, two were significantly predicted by the child’s birth order (a proxy for sub-adult communicators present in the household), and the rest did not retain any significant AMC predictors within the best fitting models (Table 4). As this paper focuses on the effect of AMC on communicative outcomes, this section

AMC exposure influences communicative behavior

These results show that AMC exposure likely influences some communicative behaviors, and that these differences are due to AMC received in informal settings rather than formal childcare settings. There were no effects of attending formal childcare, regardless of facility type, suggesting that at least at this age, formal AMC may have little impact on the development of communicative behaviors. Instead, what differences were attributable to AMC are a result of exposure to caregivers within the

Conclusions

These results are indicative of interesting next steps required to better understand how AMC at the household level, particularly in terms of sibling dynamics, impacts the development of communicative behaviors during infancy. Some behaviors are impacted by Household AMC, however, these relations are not in a uniform direction. Additionally, the effect of birth order (or the number of sub-adult communicators present in the house) on communicative behaviors is not uniform. Ultimately, this study

Funding

This work was supported by: the National Science Foundation [Award Number: BCS-1752542]; the University of Arizona’s (UA’s) School of Anthropology [W. & N. Sullivan Research Scholarship Fund and Reicker Endowment]; UA’s Confluencenter for Creative Inquiry; UA’s Social and Behavioral Sciences Research Institute; and UA’s Graduate and Professional Student Council.

Declaration of Competing Interest

None.

Acknowledgements

The author would like to extend special thanks to the participating mothers and children for their time, without which this study would not have been possible. The author also thanks Your Family’s Journey, Tucson Moms Group, Tucson Meet up Moms Group, and the many other local groups that shared recruitment information to potential participants. The author is grateful to the University of Arizona’s Frances McClelland Institute for Children, Youth, and Families, Dr. Andrea Romero, and Feliz Baca

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