Sibling Competition & Growth Tradeoffs. Biological vs. Statistical Significance.
ABSTRACT: Early childhood growth has many downstream effects on future health and reproduction and is an important measure of offspring quality. While a tradeoff between family size and child growth outcomes is theoretically predicted in high-fertility societies, empirical evidence is mixed. This is often attributed to phenotypic variation in parental condition. However, inconsistent study results may also arise because family size confounds the potentially differential effects that older and younger siblings can have on young children's growth. Additionally, inconsistent results might reflect that the biological significance associated with different growth trajectories is poorly understood. This paper addresses these concerns by tracking children's monthly gains in height and weight from weaning to age five in a high fertility Maya community. We predict that: 1) as an aggregate measure family size will not have a major impact on child growth during the post weaning period; 2) competition from young siblings will negatively impact child growth during the post weaning period; 3) however because of their economic value, older siblings will have a negligible effect on young children's growth. Accounting for parental condition, we use linear mixed models to evaluate the effects that family size, younger and older siblings have on children's growth. Congruent with our expectations, it is younger siblings who have the most detrimental effect on children's growth. While we find statistical evidence of a quantity/quality tradeoff effect, the biological significance of these results is negligible in early childhood. Our findings help to resolve why quantity/quality studies have had inconsistent results by showing that sibling competition varies with sibling age composition, not just family size, and that biological significance is distinct from statistical significance.
Project description:<h4>Background</h4>Children in Malawi face nutritional risks related to low-quality diets and chronic malnutrition.<h4>Objective</h4>This study evaluated the impact of a 1-y early childhood development (ECD) center-based agriculture and nutrition intervention aimed at improving household production diversity, maternal knowledge on child nutrition and feeding practices, and children's diets and anthropometric measures.<h4>Methods</h4>A longitudinal cluster-randomized controlled trial was implemented in 60 community-based childcare centers (CBCCs), covering 1248 preschool children (aged 36-72 mo) and 304 younger siblings (aged 6-24 mo). CBCCs were randomly assigned to 1) a control group providing the Save the Children's ECD program or 2) a treatment group providing a standard ECD program with additional activities to improve nutritious food production and behavior change communication to improve diets and care practices for young children. Primary outcomes were household production and production diversity, preschooler enrollment and attendance, and dietary intake measured by quantitative 24-h recall and minimum diet diversity for younger siblings. Secondary outcomes included anthropometric measures for preschoolers and younger siblings, child development scores for preschoolers, and women's asset ownership and time use (the latter 2 are not discussed in this article). We used difference-in-difference (DID) estimates to assess impacts.<h4>Results</h4>Compared with the control group, preschool children in the intervention group had greater increases in nutrient intakes and in dietary diversity. No impacts on anthropometric measures were seen in preschoolers. Younger siblings in the intervention group had greater increases in height-for-age z scores than did children in the control group (DID: 0.44; P < 0.05) and greater reductions in the prevalence of stunting (DID: -17 percentage points; P < 0.05). The plausibility of the impact on growth in younger siblings was supported by effects along program impact pathways, including production of nutritious foods, caregiver knowledge, and dietary diversity.<h4>Conclusion</h4>Implementing an integrated agriculture and nutrition intervention through an ECD platform benefited children's diets and reduced stunting among younger siblings of targeted preschoolers. This trial was registered on the ISRCTN registry as ISCRCTN96497560.
Project description:This study examined the influence of younger siblings on children's understanding of second-order false belief. In a representative community sample of firstborn children (N=229) with a mean age of 7years (SD=4.58), false belief was assessed during a home visit using an adaptation of a well-established second-order false belief narrative enacted with Playmobil figures. Children's responses were coded to establish performance on second-order false belief questions. When controlling for verbal IQ and age, the existence of a younger sibling predicted a twofold advantage in children's second-order false belief performance, yet this was the case only for firstborns who experienced the arrival of a sibling after their second birthday. These findings provide a foundation for future research on family influences on social cognition.
Project description:In animals that breed cooperatively, adult individuals will sometimes delay reproduction to act as helpers at the nest who raise young that are not their genetic offspring. It has been proposed that humans are also a cooperatively breeding species because older daughters, grandmothers, and other kin and nonkin may provide significant childcare. Through a prospective cohort study of children's (n = 1,700) growth and survival in the Dogon of Mali, I show that cooperative breeding theory is a poor fit to the family dynamics of this population. Rather than helping each other, siblings competed for resources, producing a tradeoff between the number of maternal siblings and growth and survival. It did not take a village to raise a child; children fared the same in nuclear as in extended families. Of critical importance was the degree of polygyny, which created conflicts associated with asymmetries in genetic relatedness. The risk of death was higher and the rate of growth was slower in polygynous than monogamous families. The hazard of death for Dogon children was twofold higher if the resident paternal grandmother was alive rather than dead. This finding may reflect the frailty of elderly grandmothers who become net consumers rather than net producers in this resource-poor society. Mothers were of overwhelming importance for child survival and could not be substituted by any category of kin or nonkin. The idea of cooperative breeding taken from animal studies is a poor fit to the complexity and diversity of kin interactions in humans.
Project description:For organisms with a complex life cycle, a large larval size is generally beneficial, but it may come at the expense of prolonged development. Individuals that grow fast may avoid this tradeoff and switch habitats at both a larger size and younger age. A fast growth rate itself can be costly, however, as it requires greater resource intake. For parasites, fast larval growth is assumed to increase the likelihood of host death before transmission to the next host occurs. Using the tapeworm Schistocephalus solidus in its copepod first intermediate host, I investigated potential constraints in the parasite's larval life history. Fast-growing parasites developed infectivity earlier, indicating there is no functional tradeoff between size and developmental time. There was significant growth variation among full-sib worm families, but fast-growing sibships were not characterized by lower host survival or more predation-risky host behavior. Parental investment also had little effect on larval growth rates. The commonly assumed constraints on larval growth and development were not observed in this system, so it remains unclear what prevents worms from exploiting their intermediate hosts more aggressively.
Project description:Youth's experiences with romantic relationships during adolescence and young adulthood have far reaching implications for future relationships, health, and well-being; yet, although scholars have examined potential peer and parent influences, we know little about the role of siblings in youth's romantic relationships. Accordingly, this study examined the prospective longitudinal links between Mexican-origin older and younger siblings' romantic relationship experiences and variation by sibling structural and relationship characteristics (i.e., sibling age and gender similarity, younger siblings' modeling) and cultural values (i.e., younger siblings' familism values). Data from 246 Mexican-origin families with older (M = 20.65 years; SD = 1.57; 50 % female) and younger (M = 17.72 years; SD = .57; 51 % female) siblings were used to examine the likelihood of younger siblings' involvement in dating relationships, sexual relations, cohabitation, and engagement/marriage with probit path analyses. Findings revealed older siblings' reports of involvement in a dating relationship, cohabitation, and engagement/marriage predicted younger siblings' relationship experiences over a 2-year period. These links were moderated by sibling age spacing, younger siblings' reports of modeling and familism values. Our findings suggest the significance of social learning dynamics as well as relational and cultural contexts in understanding the links between older and younger siblings' romantic relationship experiences among Mexican-origin youth.
Project description:<h4>Background</h4>Dental fear and anxiety (DFA) is a major issue affecting children's oral health and clinical management. This study investigates the association between children's DFA and family related factors, including parents' DFA, parenting styles, family structure (nuclear or single-parent family), and presence of siblings.<h4>Methods</h4>A total of 405 children (9-13 years old) and their parents were recruited from 3 elementary schools in Hong Kong. Child's demographic and family-related information was collected through a questionnaire. Parents' and child's DFA were measured by using the Corah Dental Anxiety Scale (CDAS) and Children Fear Survey Schedule-Dental Subscale (CFSS-DS), respectively. Parenting styles were gauged by using the Parent Authority Questionnaire (PAQ).<h4>Results</h4>DFA was reported by 33.1% of children. The mean (SD) CFSS-DS score was 29.1 (11.0). Children with siblings tended to report DFA (37.0% vs. 24.1%; p?=?0.034) and had a higher CFSS-DS score (29.9 vs. 27.4; p?=?0.025) as compared with their counterpart. Children from single-parent families had lower CFSS-DS score as compared with children from nuclear families (??=?-?9.177; p?=?0.029). Subgroup analysis showed a higher CFSS-DS score among boys with siblings (??=?7.130; p?=?0.010) as compared with their counterpart; girls' from single-parent families had a lower CFSS-DS score (??=?-?13.933; p?=?0.015) as compared with girls from nuclear families. Children's DFA was not associated with parents' DFA or parenting styles (p?>?0.05).<h4>Conclusions</h4>Family structure (nuclear or single-parent family) and presence of siblings are significant determinants for children's DFA. Parental DFA and parenting style do not affect children's DFA significantly.
Project description:We explored whether young children exhibit subtypes of behavioral sequences during sibling interaction. Ten-minute, free-play observations of over 300 sibling dyads were coded for positivity, negativity and disengagement. The data were analyzed using growth mixture modeling (GMM). Younger (18-month-old) children's temporal behavioral sequences showed a harmonious (53%) and a casual (47%) class. Older (approximately four-year-old) children's behavior was more differentiated revealing a harmonious (25%), a deteriorating (31%), a recovery (22%) and a casual (22%) class. A more positive maternal affective climate was associated with more positive patterns. Siblings' sequential behavioral patterns tended to be complementary rather than reciprocal in nature. The study illustrates a novel use of GMM and makes a theoretical contribution by showing that young children exhibit distinct types of temporal behavioral sequences that are related to parenting processes.
Project description:Compared to great apes, humans maintain a relatively rapid reproductive pace despite long periods of dependency. This seemingly contradictory set of traits is made possible by weaning offspring before nutritional independence and alloparents who help provide care. In traditional societies, this help may be provided to mothers in part by their juvenile offspring who carry, supervise, or provision younger siblings. In contrast to humans, chimpanzees (Pan troglodytes) are nutritionally independent after weaning, yet juveniles continue to travel with their mother and younger sibling for an additional 4-5 years. This continued association could be costly to the mother if she continues to invest in weaned offspring. Alternately, while juvenile chimpanzees do not typically provision younger siblings, their presence and social interaction with infants may allow mothers to focus on other tasks. In this study, we investigate the costs and benefits to mothers of continued association with juveniles in wild chimpanzees. Using 26 years of long-term behavioral data we examined how maternal activity budgets varied based on the presence of a dependent juvenile offspring. We found that continued social interaction between mothers and juveniles does not influence the mother's time allocated to interacting with the younger infant, her feeding, resting, or travel time, or time socializing with other community members. Instead, mothers may benefit from the additional social interaction and/or relationship with their older offspring. Using 45 years of demographic data we found that those offspring who had an older sibling tended to be more likely to survive each year from birth to 8 years than those without an older sibling. Additionally, interbirth intervals were more likely to end when the female had an older offspring present. A mutually beneficial mother-juvenile dynamic in great apes provides insight into continued association between mothers and offspring after nutritional independence and the emergence of juvenile helping during hominin evolution.
Project description:High and variable pre-weaning mortality is a persistent problem in laboratory mouse breeding. Assuming a modest 15% mortality rate across mouse strains, means that approximately 1 million more pups are produced yearly in the EU to compensate for those which die. This paper presents the first large study under practical husbandry conditions to determine the risk factors associated with mouse pre-weaning mortality. We analysed historical records from 219,975 pups from two breeding facilities, collected as part of their management routine and including information on number of pups born and weaned per litter, parents' age and identification, and dates of birth and death of all animals. Pups were counted once in their first week of life and at weaning, and once every one or two weeks, depending on the need for cage cleaning. Dead pups were recorded as soon as these were found during the daily cage screening (without opening the cage). It was hypothesized that litter overlap (i.e. the presence of older siblings in the cage when new pups are born), a recurrent social configuration in trio-housed mice, is associated with increased newborn mortality, along with advanced dam age, large litter size, and a high number and age of older siblings in the cage. The estimated probability of pup death was two to seven percentage points higher in cages with litter overlap compared to those without. Litter overlap was associated with an increase in death of the entire litter of five and six percentage points, which represent an increase of 19% and 103% compared to non-overlapped litters in the two breeding facilities, respectively. Increased number and age of older siblings, advanced dam age, small litter size (less than four pups born) and large litter size (over 11 pups born) were associated with increased probability of pup death.
Project description:BACKGROUND:Lifestyle interventions to prevent paediatric obesity often target family and peer settings; their success is likely to depend on the influence that peers and families exert on children's lifestyle behaviors at different developmental stages. OBJECTIVE:First, to determine whether children's lifestyle behavior more closely resembles their peers' or siblings' behaviors. Secondly, to investigate longitudinally whether children's behavioral change is predicted by that of their peers or their siblings as they grow older. METHODS:The European prospective IDEFICS/I.Family cohort (baseline survey: 2007/2008, first follow-up: 2009/2010, and second follow-up: 2013/2014) aims at investigating risk factors for overweight and related behaviors during childhood and adolescence. The present investigation includes 2694 observations of children and their siblings aged 2 to 18 years. Peers were defined as same-sex, same-age children in the same community and identified from the full cohort. The longitudinal analysis (mean follow-up time: 3.7 years) includes 525 sibling pairs. Children's lifestyle behaviors including fast food consumption (frequency/week), screen time (hours/week) and sports club participation (hours/week) were assessed by questionnaire. Data were analyzed using multilevel linear models. RESULTS:Children's lifestyle behavior was associated with the respective behavior of their peers and sibling for all 3 behaviors. For fast food consumption, the peer resemblance was more than 6-fold higher than the sibling resemblance and the peer resemblance surpassed the sibling resemblance by the age of 9-10 years. The similarities with peers for fast food consumption and screen time steadily increased, while the similarities with siblings steadily decreased with increasing age of the children (Pinteraction < 0.001). In contrast, the relative importance of peers and siblings on sports club duration did not vary by the age of the children. Longitudinal results showed that children's changes in fast food consumption were more strongly associated with those in their peer group than their sibling, in particular if the age gap between siblings was large. CONCLUSION:In conclusion, our results support the implementation of multi-setting interventions for improving lifestyle behaviors in children. Our findings might also guide future intervention studies in the choice of timing and setting in which interventions are likely to be most effective. From the ages of 9-10 years onwards, family- or home-based interventions targeting children's fast food intake and screen time behavior may become less effective than school- or community-based interventions aimed at peer groups.