Laboratoire de Géologie de Lyon: Terre, Planètes, et Environnement, Université de Lyon, École Normale Supérieure de Lyon, Université Lyon 1, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5276, 69364 Lyon, France;
Team Evolution of Vertebrate Dentition, Institut de Génomique Fonctionnelle de Lyon, École Normale Supérieure de Lyon, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5242, Université Claude Bernard Lyon 1, 69364 Lyon, France.
Proc Natl Acad Sci U S A. 2017 Jun 13;114(24):6268-6273. doi: 10.1073/pnas.1704412114. Epub 2017 May 30.
Weaning practices differ among great apes and likely diverged during the course of human evolution, but behavioral inference from the fossil record is hampered by a lack of unambiguous biomarkers. Here, we show that early-life dietary transitions are recorded in human deciduous tooth enamel as marked variations in Ca isotope ratios (δCa). Using a sequential microsampling method along the enamel growth axis, we collected more than 150 enamel microsamples from 51 deciduous teeth of 12 different modern human individuals of known dietary histories, as well as nine enamel samples from permanent third molars. We measured and reconstructed the evolution of Ca/Ca ratios in enamel from in utero development to first months of postnatal development. We show that the observed variations of δCa record a transition from placental nutrition to an adult-like diet and that Ca isotopes reflect the duration of the breastfeeding period experienced by each infant. Typically, the δCa values of individuals briefly or not breastfed show a systematic increase during the first 5-10 mo, whereas individuals with long breastfeeding histories display no measurable variation in δCa of enamel formed during this time. The use of Ca isotope analysis in tooth enamel allows microsampling and offers an independent approach to tackle challenging questions related to past population dynamics and evolution of weaning practices in hominins.
断乳行为在大型猿类中存在差异，并且可能在人类进化过程中发生了分歧，但由于缺乏明确的生物标志物，因此很难从化石记录中推断出行为。在这里，我们表明，人类乳牙牙釉质中的钙同位素比值（δCa）的明显变化记录了生命早期的饮食转变。我们使用沿釉质生长轴的顺序微采样方法，从 12 个具有已知饮食史的不同现代人类个体的 51 颗乳牙中收集了 150 多个牙釉质微样本，以及 9 个来自第三磨牙的牙釉质样本。我们测量并重建了从胎儿发育到出生后第一个月的牙釉质中 Ca/Ca 比值的演变。我们表明，观察到的 δCa 变化记录了从胎盘营养到成人饮食的转变，并且钙同位素反映了每个婴儿经历的母乳喂养期的持续时间。通常，短暂或未母乳喂养的个体的 δCa 值在头 5-10 个月期间会系统增加，而母乳喂养时间长的个体在此期间形成的牙釉质的 δCa 值没有可测量的变化。牙釉质中钙同位素分析的使用允许进行微采样，并提供了一种独立的方法来解决与过去人口动态和人类断乳实践进化有关的具有挑战性的问题。
