McKerracher Luseadra J, Collard Mark, Altman Rachel M, Sellen Daniel, Nepomnaschy Pablo A
Human Evolutionary Studies Program, Simon Fraser University, Burnaby, British Columbia, Canada, V5A 1S6.
Department of Archaeology, Simon Fraser University, Burnaby, British Columbia, Canada, V5A 1S6.
Am J Phys Anthropol. 2017 Apr;162(4):616-626. doi: 10.1002/ajpa.23125. Epub 2016 Nov 3.
The causes of variation in breastfeeding duration in humans are poorly understood, but life history factors related to maternal energetics drive much of the variation in lactation duration in nonhuman animals. With this in mind, we investigated whether four energy-related factors influence variation in breastfeeding duration in a non-industrial human population: (1) mortality risk during mother's development (assessed via mother's adult height), (2) reliance on nutrient-dense weaning foods, (3) access to and need for help with infant feeding and care ("allomaternal care"), and (4) maternal tradeoffs between current and future reproduction (measured via child's birth order).
The data pertain to 51 Kakchiquel-speaking Maya mothers and 283 children from a village in rural Guatemala. We developed a linear mixed model to evaluate the relationships between breastfeeding duration and the energy-related factors.
Duration of breastfeeding was associated with two of the energy-related factors in the ways we predicted but not with the other two. Contrary to predictions, taller mothers breastfed for shorter periods and we found no evidence that weanling diet quality impacts breastfeeding duration. As predicted, women who had more help with infants breastfed for shorter periods, and later-born infants breastfed longer than earlier-born ones.
The results regarding allomaternal care suggest that help reduces mothers' lactation demands. The energy saved may be redirected to increasing fecundity or investment in other children. The birth order result suggests that children born to mothers nearing reproductive senescence receive higher levels of investment, which likely impacts children's fitness.
人类母乳喂养持续时间变化的原因尚不清楚，但与母体能量学相关的生活史因素驱动了非人类动物泌乳持续时间的大部分变化。考虑到这一点，我们调查了四个与能量相关的因素是否会影响非工业化人类群体母乳喂养持续时间的变化：（1）母亲发育期间的死亡风险（通过母亲的成年身高评估），（2）对营养丰富的断奶食物的依赖，（3）获得婴儿喂养和护理帮助（“异亲照料”）的机会和需求，以及（4）母体在当前和未来繁殖之间的权衡（通过孩子的出生顺序衡量）。
数据涉及来自危地马拉农村一个村庄的51名说卡克奇克尔语的玛雅母亲和283名儿童。我们建立了一个线性混合模型来评估母乳喂养持续时间与能量相关因素之间的关系。
母乳喂养持续时间与我们预测的两个能量相关因素有关，但与另外两个因素无关。与预测相反，个子较高的母亲母乳喂养时间较短，并且我们没有发现断奶饮食质量影响母乳喂养持续时间的证据。正如预测的那样，在婴儿护理方面得到更多帮助的女性母乳喂养时间较短，晚出生的婴儿比早出生的婴儿母乳喂养时间更长。
关于异亲照料的结果表明，帮助减少了母亲的泌乳需求。节省的能量可能会重新导向增加生育力或对其他孩子的投资。出生顺序的结果表明，接近生殖衰老的母亲所生的孩子获得更高水平的投资，这可能会影响孩子的健康状况。
