Dental size variability in Central African Pygmy hunter-gatherers and Bantu-speaking farmers

From hunter-gatherers to food producers: New dental insights into the Nile Valley population history (Late Paleolithic-Neolithic)

OBJECTIVES

This study presents biological affinities between the last hunter-fisher-gatherers and first food-producing societies from the Nile Valley. We investigate odontometric and dental tissue proportion changes between these populations from the Middle Nile Valley and acknowledge the biological processes behind them.

MATERIALS AND METHODS

Dental remains of 329 individuals from Nubia and Central Sudan that date from the Late Pleistocene to the mid-Holocene are studied. Using 3D imaging techniques, we investigated outer and inner metric aspects of upper central incisors, and first and second upper molars.

RESULTS

Late Paleolithic and Mesolithic foragers display homogeneous crown dimensions, dental tissue proportions, and enamel thickness distribution. This contrasts with Neolithic trends for significant differences from earlier samples on inner and outer aspects. Finally, within the Neolithic sample differences are found between Nubian and Central Sudanese sites.

DISCUSSION

Substantial dental variation appears to have occurred around 6000 bce in the Nile Valley, coinciding with the emergence of food-producing societies in the region. Archeological and biological records suggest little differences in dietary habits and dental health during this transition. Furthermore, the substantial variations identified here would have happened in an extremely short time, a few centuries at most. This does not support in situ diet-related adaptation. Rather, we suggest these data are consistent with some level of population discontinuity between the Mesolithic and Neolithic samples considered here. Complex settlement processes could also explain the differences between Nubia and Central Sudan, and with previous results based on nonmetric traits.

Dental size variation in admixed Latin Americans: Effects of age, sex and genomic ancestry

Dental size variation in modern humans has been assessed from regional to worldwide scales, especially under microevolutionary and forensic contexts. Despite this, populations of mixed continental ancestry such as contemporary Latin Americans remain unexplored. In the present study we investigated a large Latin American sample from Colombia (N = 804) and obtained buccolingual and mesiodistal diameters and three indices for maxillary and mandibular teeth (except third molars). We evaluated the correlation between 28 dental measurements (and three indices) with age, sex and genomic ancestry (estimated using genome-wide SNP data). In addition, we explored correlation patterns between dental measurements and the biological affinities, based on these measurements, between two Latin American samples (Colombians and Mexicans) and three putative parental populations: Central and South Native Americans, western Europeans and western Africans through PCA and DFA. Our results indicate that Latin Americans have high dental size diversity, overlapping the variation exhibited by the parental populations. Several dental dimensions and indices have significant correlations with sex and age. Western Europeans presented closer biological affinities with Colombians, and the European genomic ancestry exhibited the highest correlations with tooth size. Correlations between tooth measurements reveal distinct dental modules, as well as a higher integration of postcanine dentition. The effects on dental size of age, sex and genomic ancestry is of relevance for forensic, biohistorical and microevolutionary studies in Latin Americans.

Morphological variation of the deciduous second molars in the Baka Pygmies

The Baka Pygmies are known for their short stature resulting from a reduced growth rate during infancy. They are peculiar also for their teeth erupt earlier than in any other African population, and their posterior dentition is larger than in non-Pygmy populations. However, the Baka's dental morphology, like several other aspects of their biology, is still understudied. Here, we explore the variation of the Baka's deciduous upper and lower second molars (dm2s) in comparison to a geographically heterogeneous human sample by means of 3D geometric morphometrics and analysis of dental traits. Our results show that the different populations largely overlap based on the shape of their dm2s, especially the lower ones. Their distal region and the height of the dentinal crown differ the most, with the Baka showing the most extreme range of variation. Upper and lower dm2s covary to a great extent (RV = 0.82). The Baka's and South Americans' dm2s were confirmed among the largest in our sample. Despite the Baka's unique growth pattern, long-lasting isolation, and extreme dental variation, it is not possible to distinguish them from other populations based on their dm2s' morphology only.

Age-related tooth wear in African rainforest hunter-gatherers

OBJECTIVES

Central African small-scale foragers subsist primarily on hunting game activities and wild plant-food gathering. Starch-rich tubers are underground storage organs (USOs) and staple food resources in savanna and tropical rainforests. However, little is known about the effect of USO consumption on tooth wear development in living hunter-gatherers. We report age- and sex-dependent tooth wear rates in forest-dwelling Baka Pygmies with well-documented wild-yam-tuber-based diet to explore the long-term impact of USO mechanical hardness and abrasiveness on the wearing down of the teeth.

MATERIALS AND METHODS

Percentages of dentine exposure (PDEs) of permanent left mandibular first molars (M₁ ) were recorded using in vivo high-resolution replicas of Baka individuals (aged 8-33 years), inhabiting Le Bosquet district in Cameroon (Western Africa). Regression and covariance analyses were used to test the effect of individual aging by sex on PDE rates.

RESULTS

We found a strong increase of PDE by age among Baka individuals. No evidence of sexual dimorphism in wear patterns suggests similar sex-related dietary and masticatory demands during growth. Overall, greatest dentine exposure values ≈4% denote unexpected slow wear down rates for foraging diets relying on USO consumption.

DISCUSSION

The low molar wear rates with age found in Baka Pygmies contrast with extensive wear rates in savanna-dwelling foragers, reflecting differences in thermal processing techniques affecting fracture toughness and grittiness of mechanically challenging foods. Our findings reveal that culture-specific dietary proclivities influence tooth wear among foraging behaviors with important implications in hominin dietary versatility and abrasive stress on chewing surfaces.

Tooth dimensions and body size in a Pygmy population

Background: The relationship between tooth size and stature has been analysed extensively at the interspecies level but has received less attention at the intraspecies level. The relationship between these two parameters does not seem to be the same among modern human populations.Aim: The aim of this study is to analyse the relationship between tooth dimensions and body measurements in the Baka Pygmies.Subjects and methods: Height, weight, and tooth dimensions were obtained for 45 adult Baka females and 17 males from Le Bosquet (Cameroon). Correlations were obtained between the variables and compared to results for other human populations.Results: The Baka population is distinctive in the small number of significant correlations. Only two buccolingual diameters among Baka females show any significant correlation with height. The lack of significant correlations between tooth dimensions and body dimensions among the Baka means that changes in body size are accompanied by random variations in tooth dimensions.Conclusion: The absence of correlations may be accounted for by the impact of environmental effects on the somatic growth of the Baka producing a Pygmy phenotype adapted to live in the forest. It is worth noting that many correlations become significant when sexes are pooled.