Amanda Veile

Birth and Breastfeeding Dynamics in a Modernizing Indigenous Community

Background: Changes in health care access and birthing practices may pose barriers to optimal breastfeeding in modernizing rural populations. Objectives: We evaluated temporal and maternal age-related trends in birth and breastfeeding in a modernizing Maya agriculturalist community. We tested 2 hypotheses: (1) home births would be associated with better breastfeeding outcomes than hospital births, and (2) vaginal births would be associated with better breastfeeding outcomes than cesarean births. Methods: We interviewed 58 Maya mothers (ages 21-85) regarding their births and breastfeeding practices. General linear models were used to evaluate trends in birthing practices and breastfeeding outcomes (timing of breastfeeding initiation, use of infant formula, age of introduction of complementary feeding, and breastfeeding duration). We then compared breastfeeding outcomes by location (home or hospital) and mode of birth (vaginal or cesarean). Results: Timing of breastfeeding initiation and the rate of formula feeding both increased significantly over time. Younger mothers introduced complementary foods earlier, breastfed for shorter durations, and formula fed more than older mothers. Vaginal hospital births were associated with earlier breastfeeding initiation and longer breastfeeding durations than home births. Cesarean births were associated with later breastfeeding initiation, shorter breastfeeding durations, and more formula feeding than vaginal hospital births. Conclusion: We have observed temporal and maternal age-related trends toward suboptimal breastfeeding patterns in the Maya community. Contrary to our first hypothesis, hospital births per se were not associated with negative breastfeeding outcomes. In support of our second hypothesis, cesarean versus vaginal births were associated with negative breastfeeding outcomes.

Infant allocare in traditional societies

Across human societies infants receive care from both their mothers and others. Reproductive cooperation raises two important questions: how does allocare benefit mothers and infants, and why do caretakers help mothers when they could spend their time in other, perhaps more valuable ways? We use behavioral and biological data from three small-scale societies to evaluate 1) how allocare affects a nursing mothers time, 2) whether a mothers birth interval length, surviving fertility and infant weight vary as a function of the childcare help that she receives, and 3) the opportunity cost for helpers to spend time caring for children. Across our hunter-gatherer and agricultural samples we find that on average mothers provide 57% of the direct care that an infant receives and allocaretakers 43% (±20%). Model results show that for every 10% increase in allocare the probability that a mother engages in direct care diminishes by 25%, a potential savings of an estimated 165 kcals per day. While allocare has a significant immediate impact on mothers time, no detectable effect on delayed fitness measures (birth interval and surviving fertility) or on infant weight status was evident. Cross culturally we find that other than mothers, siblings spend the most time caretaking infants, and they do so without compromising the time that they might otherwise spend in play, economic activities or education. The low opportunity cost for children to help offers an alternative explanation why juveniles are common caretakers in many societies, even in the absence of delayed indirect fitness benefits. While we expect specific patterns to vary cross culturally, these results point to the importance of infant allocare and its immediate time benefits for mothers to maintain flexibility in balancing the competing demands to support both older and younger children.

Sibling Competition & Growth Tradeoffs. Biological vs. Statistical Significance

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.

Infant growth and the thymus: Data from two South American native societies

The thymus plays an important role in the development of the immune system, yet little is known about the patterns and sources of variation in postnatal thymic development. The aim of this study is to contribute cross‐cultural data on thymus size in infants from two South American native populations, the Tsimane of Bolivia and the Pumé of Venezuela. Thymic ultrasonography was performed and standard anthropometric measures collected from 86 Tsimane and Pumé infants. Patterns of infant growth and thymus size were compared between the two populations and the relationship between nutritional status and thymus size was assessed. Despite nearly identical anthropometric trajectories, Tsimane infants had larger thymuses than Pumé infants at all ages. Population, infant age, and infant mid‐upper arm circumference were significant predictors of thymus area in the Tsimane and Pumé infants. This finding reveals a cross‐cultural difference in thymus size that is not driven by nutritional status. We suggest that future studies focus on isolating prenatal and postnatal environmental factors underlying cross‐cultural variation in thymic development. Am. J. Hum. Biol., 2012.

Childhood body mass is positively associated with cesarean birth in Yucatec Maya subsistence farmers.

The epidemiologic link between cesarean birth and childhood obesity is unresolved, partly because most studies come from industrialized settings where many post‐birth factors affect the risk for obesity. We take advantage of an unusual ethnographic situation where hospital and cesarean birth modes have recently been introduced among Yucatec Maya subsistence farmers, but young children have had minimal exposure to the nutritional transition. While we expect to find very low rates of childhood obesity, we predict that cesarean‐born children will be larger and heavier than vaginally born children.

Pregnancy, Birth, and Babies: Motherhood and Modernization in a Yucatec Village

We examine the medicalization of birth in a Mexican Yucatec Maya farming community over the past 65 years. Our findings are drawn from longitudinal demographic data collection (1992–2014) and 56 maternal ethnographic interviews. We describe and contrast the maternal experience of three cohorts of women whose reproductive careers transpired in the context of energetic and epidemiologic transitions: Cohort 1 women had their first birth from 1950 to 1977, under conditions of traditional midwifery, subsistence farming, and energetic stress; Cohort 2 women had their first birth from 1978 to 1999; a time of energetic transition as laborsaving technology and some medical care was introduced; and Cohort 3 women had their first birth from 2000 to 2014, a period of increasing modernization and epidemiologic transition. Hospital births have become increasingly common since the late 1990s and are associated with increased birth complications, medical interventions, nonelective cesarean section procedures, postpartum rest periods, and increased formula feeding, as well as decreased maternal intrapartum support. Still many Maya mothers retain several traditional practices; some visit the traditional birth attendant (midwife) for prenatal and postnatal care, and prolonged and intensive breastfeeding is still the norm. Infant mortality rates from Cohort 3 are higher than Mexico’s national average, but in Cohorts 1 and 2, they were lower than Mexico’s national average. A number of unique factors may have contributed to the maintenance of low maternal-infant mortality in this community, even in times of energetic stress and when biomedical care was lacking. These include the effective Maya midwifery system, intensive breastfeeding practices, and a sanitary water supply.

Hunter-gatherer diets and human behavioral evolution

Human behavior and physiology evolved under conditions vastly different from those which most humans inhabit today. This paper summarizes long-term dietary studies conducted on contemporary hunter-gatherer populations (sometimes referred to as foragers). Selected studies for the most part that use evolutionary theoretical perspectives and data collection methods derived from the academic field of human behavioral ecology, which derives relatively recently from the fields of evolutionary biology, ethology, population biology and ecological anthropology. I demonstrate how this body of research illuminates ancestral patterns of food production, consumption and sharing, infant feeding, and juvenile subsistence contributions in hunter-gatherer economies. Insights from hunter-gatherer studies are then briefly discussed within the context of better-studied human populations that are Westernized, Educated, Industrialized, Rich, and Democratic (WEIRD).