Early life of Neanderthals

Abstract

The early onset of weaning in modern humans has been linked to the high nutritional demand of brain development that is intimately connected with infant physiology and growth rate. In Neanderthals, ontogenetic patterns in early life are still debated, with some studies suggesting an accelerated development and others indicating only subtle differences vs. modern humans. Here we report the onset of weaning and rates of enamel growth using an unprecedented sample set of three late (∼70 to 50 ka) Neanderthals and one Upper Paleolithic modern human from northeastern Italy via spatially resolved chemical/isotopic analyses and histomorphometry of deciduous teeth. Our results reveal that the modern human nursing strategy, with onset of weaning at 5 to 6 mo, was present among these Neanderthals. This evidence, combined with dental development akin to modern humans, highlights their similar metabolic constraints during early life and excludes late weaning as a factor contributing to Neanderthals' demise.

Keywords: Neanderthal ontogeny; dental histology; life histories; nursing strategy; spatially resolved chemical analyses.

Fig. 1.

Geographical, paleoecological, and chronological framework. (A) Oxygen isotope curve from North Greenland Ice Core Project (22), with Greenland Stadials 5 to 21 highlighted. Chronologies of the human specimens are also reported (as detailed in the SI Appendix); Fumane 2 is UPMH (green), while Nadale 1, Riparo Broion 1, and Fumane 1 are Neanderthals (yellow). (B–D) Modeled Alpine glacier extent during the time intervals of the teeth recovered at the sites of Fumane Cave (B and C), Riparo Broion (C), and Nadale (D); location within Italy is also shown (Inset). Simulations show a high temporal variability in the total modeled ice volume during Marine Isotope Stages 4 (70-ka snapshot) and 3 (50-40-ka snapshots) with glaciers flowing into the major valleys and possibly even onto the foreland (23).

Fig. 2.

Dental crown growth parameters. (A) Postnatal crown formation time in days from birth for the four investigated fossil deciduous teeth relative to the range of variability reported in literature for modern and archaeological individuals (red, blue, green lines). (B) Box plot of the daily secretion rate (DSR) variation in the first 100 µm from the enamel–dentine junction (min., second quartile, median, third quartile, max.) in comparison to the corresponding variability (min., mean, max.) of modern humans (MH), reassessed from refs. –. (C) Box plot of the daily secretion rate variation across the whole crown (min., second quartile, median, third quartile, max.) and range of variation (min., mean, max.) of modern humans (MH), reassessed from refs. –. Ldm1, lower deciduous first molar; Ldm2, lower deciduous second molar; Udc, upper deciduous canine; Ldi2, lower deciduous later incisor.

Fig. 3.

Nursing histories from time-resolved Sr/Ca variation in Middle-Upper Paleolithic deciduous teeth. NEA, Neanderthal; UPMH, Upper Paleolithic modern human. The elemental profiles (Sr/Ca; Ba/Ca for comparison) were analyzed within enamel closest to the enamel–dentine junction (EDJ); [U] is reported as diagenetic alteration proxy for all fossil specimens (15) (SI Appendix, Text S4 and Fig. S13); diagenetically affected sections are grayed out. All are plotted relative to secretion time (in days); the birth event is highlighted by a vertical line in each plot. Elemental ratios are reported mass (weight)-based, not as mol/mol (15). The compositional profiles were smoothed with a locally weighted polynomial regression fit (LOWESS), with its associated SE range (±3 SE) for each predicted value. (A) Comparison between two contemporary individuals with known feeding histories, MCS1 (exclusively breastfed) and MCS2 (exclusively formula-fed); t1, transitional period, i.e., first time solid food starts; t2, progressively reduced breastfeeding during day; t3, transitional period ends, end of breastfeeding. (B) Nadale 1: the slight decrease of Sr/Ca indicates exclusive breastfeeding until the end of crown formation (4.7 mo). (C) Fumane 1: Sr/Ca variation indicates breastfeeding until 4 mo of age (fully comparable with MCS1 sample; SI Appendix, Fig. S6). (D) Riparo Broion 1: Sr/Ca profile indicates exclusive breastfeeding until 5 mo of age. (E) Fumane 2: 55 d of available postnatal enamel shows exclusive breastfeeding. (F) Comparative Sr/Ca profiles of all fossil specimens adjusted to the birth event; the interpolated modeled profiles were calculated based on those portions unaffected by diagenesis ([U] < 0.05 ppm), with strong smoothing parameters to reveal the biogenic signal. Riparo Broion 1, the specimen most affected by diagenesis, retains the overall outline of a breastfeeding signal (A). Further details are provided in Materials and Methods.

Fig. 4.

Mobility of the Middle-Upper Paleolithic infants via time-resolved ⁸⁷Sr/⁸⁶Sr profiles of their deciduous teeth. Gray horizontal bands represent the local Sr isotopic baselines defined via the Sr isotopic composition of archaeological rodent enamel (SI Appendix, Table S1). The birth event is indicated by a vertical line. (A and B) Nadale 1/Fumane 1: exploitation of local food resources through the entire period; (C) Riparo Broion 1: possible limited seasonal mobility (nonlocal values between ca. −45 and 85 d, ∼4 mo); (D) Fumane 2: exploitation of nonlocal food resources through the entire period.