Wintertime stress, nursing, and lead exposure in Neanderthal children

Abstract

Scholars endeavor to understand the relationship between human evolution and climate change. This is particularly germane for Neanderthals, who survived extreme Eurasian environmental variation and glaciations, mysteriously going extinct during a cool interglacial stage. Here, we integrate weekly records of climate, tooth growth, and metal exposure in two Neanderthals and one modern human from southeastern France. The Neanderthals inhabited cooler and more seasonal periods than the modern human, evincing childhood developmental stress during wintertime. In one instance, this stress may have included skeletal mobilization of elemental stores and weight loss; this individual was born in the spring and appears to have weaned 2.5 years later. Both Neanderthals were exposed to lead at least twice during the deep winter and/or early spring. This multidisciplinary approach elucidates direct relationships between ancient environments and hominin paleobiology.

Fig. 1. Analytical approach for Payre hominin molars in this study.

As shown clockwise from top left, this involves photography, micro–computed tomography (micro-CT) scanning and virtual sectioning, production of histological sections, identification of accentuated lines (including birth—dotted line with a postinitiation time of 40 days) and characterization of tooth formation time (in days), laser ablation elemental mapping, and secondary ion mass spectrometry (SIMS) analysis of oxygen isotopes. The inset in the lower left shows 16-μm sensitive high-resolution ion microprobe (SHRIMP) spots spaced every 50 μm immediately adjacent to the enamel-dentine junction (EDJ; dark line) and parallel 35-μm laser tracks in the embedding material around the tooth, which can be seen in the gold-coated section. The photograph and micro-CT model of Payre 1 are flipped for ease of visualization. E, enamel; D, dentine.

Fig. 2. Oxygen isotopes in hominin teeth from Payre.

Oxygen isotope compositions (δ¹⁸O) shown on a Vienna standard mean ocean water (VSMOW) scale measured along the EDJ at a spatial scale corresponding to approximately weekly intervals. Note that the x axis is not linear as tooth extension begins rapidly and decreases toward the cervix. Thus, isotopic values appear stretched on the left and compressed on the right. Each plot is at the same VSMOW scale with a dotted line at 18‰ for ease of comparison across teeth. (A) The modern human tooth preserved a birth line (Fig. 1), indicated here as a green vertical line 40 days after tooth initiation. (B) The Payre 6 individual preserved a birth line (Fig. 3) formed 6 days after initiation, but it was not possible to sample prenatal enamel as this line is very close to the EDJ. (C) Initial δ¹⁸O values (gray box) for Payre 336 might be influenced by diagenesis, as this region showed demineralization for the first 350 μm along the EDJ (fig. S5C).

Fig. 3. Integration of developmental, elemental, and isotopic data for Payre 6.

(A) First molar distobuccal cusp enamel development (time in days), including the birth line 6 days after enamel initiation and a marked week-long stress at 707 days (701 days of age). (B) Calcium-normalized barium (Ba/Ca) and lead (Pb/Ca) maps, with biogenic patterns indicated by arrows and brackets. The Ba/Ca map on the left shows an artificially elevated region (fig. S4), a biogenic band at 707 days after initiation, and sustained minimum values in the cervical region most likely due to weaning at 2.5 years of age. On the right, the first elevated Pb band at ~286 days after initiation corresponds to the beginning of the low Ba region in the cuspal enamel, while the second band was formed at ~772 days. It was not possible to sample the prenatal enamel exclusively as the birth line is too close to the EDJ (~20 μm away at maximum distance); thus, each innermost 35-μm laser spot includes both pre- and postnatal enamel above the dentine horn. (C) Oxygen isotope values over 2.8 years. The yellow box indicates elevated Ba/Ca values that cease 3 months before molar cusp completion. The blue vertical lines indicate the formation of the lead bands, while the red line corresponds to the elevated barium band. The other distal cusp of this tooth completed formation a few months earlier and thus does not provide a postweaning signal.

Fig. 4. Integration of developmental, elemental, and isotopic data for Payre 336.

(A) Second molar mesiobuccal cusp development (time in days), including a marked ~2-week developmental defect at 631 days and a week-long defect at 863 days (red dotted lines). (B) Calcium-normalized lead (Pb/Ca) map, with biogenic patterns indicated by blue lines registered to the temporal map. The first biogenic lead band formed at ~722 days after tooth initiation, while the second band formed after cusp completion (>1119 days). Projections of the curvature of growth lines suggest that it would have formed ~108 to 176 days after completion. (C) Oxygen isotope values (δ¹⁸O) over 3 years of tooth formation. Vertical lines on the isotopic plot reveal timing of developmental defects (red lines) and biogenic lead exposures (blue lines). No biogenic barium information was available for this tooth.