Scheifler, N. | bioRxiv Science

bioRxiv2026

Region-specific patterns of sexual shape variation in the human bony labyrinth: 3D geometric morphometric analysis of a sample with known genomic sex

The human bony labyrinth has attracted increasing interest because of its taxonomic, evolutionary, and functional significance. Although sexual dimorphism has been reported in several aspects of the temporal bone, the extent to which sex, age, size, and allometry contribute to labyrinth shape variation remains poorly understood. Here, we investigated patterns of sexual shape variation in the human bony labyrinth using three-dimensional geometric morphometrics in a sample of 98 archaeological individuals from South America with known genomic sex. Centroid size and allometric effects were assessed in a subset of 90 individuals with comparable metric scaling. In addition to analysing the complete labyrinth, the cochlea and semicircular canals were examined separately to evaluate region-specific patterns of sexual shape variation. Principal Component Analysis showed extensive overlap between females and males, and overall labyrinth shape did not differ significantly between sexes. Males exhibited significantly larger labyrinths than females, and centroid size explained a small but significant proportion of overall shape variation. Regional analyses showed no evidence of significant sexual shape differences in the cochlea or in any individual semicircular canal when analysed separately. In contrast, the combined semicircular canal system exhibited subtle but significant sexual shape variation independent of centroid size, whereas morphological disparity did not differ between sexes. The geometric comparison of the female and male consensus configurations further showed that sexual shape variation was regionally heterogeneous. Whereas the cochlea exhibited a pattern of localized changes with low directional coherence, the semicircular canals displayed more coordinated regional shape changes. The male consensus also exhibited slightly higher canal circularity across all three semicircular canals, particularly the posterior canal, while differences in canal-plane orientation remained minimal. These findings demonstrate that sexual shape variation in the human bony labyrinth is subtle and anatomically partitioned among its components. Although significant sex differences in centroid size were detected across most anatomical regions, overall labyrinth shape and cochlear morphology were primarily influenced by allometry, whereas significant sex-related shape differences were detected only when the semicircular canals were considered as an integrated anatomical system. These findings demonstrate that sexual dimorphism in the human bony labyrinth is subtle but regionally heterogeneous, with the cochlea and semicircular canals exhibiting distinct patterns of shape variation, suggesting that these structures are influenced by different developmental, functional, and evolutionary processes.

evolutionary biology↗

bioRxiv2025

The shared genomic history of Middle to Late Holocene Southern Cone populations

The Southern Cone represents the southernmost region of South America to be colonized by humans. Although ancient genomes have been sequenced from southern Patagonia, genomic data from the central Southern Cone remain temporally and spatially sparse. The archaeological record of this region documents major cultural transformations during the Middle and Late Holocene, yet their relationship to demographic processes has long been debated. Here, we present genome-wide data from 52 individuals spanning the past 5,000 years, originating from four regions of the central Southern Cone in present-day Argentina and Uruguay: the central and southern Pampas, Northwest Patagonia, the Parana River Delta and Lower Uruguay River, and the eastern lowlands of Uruguay. Genomic evidence from the Pampas reveals the presence of at least three distinct ancestries during the Middle Holocene. While genetic contacts with southern Patagonian groups were sporadic, we identify the expansion of an ancestry of unknown geographic origin by 4,800 years ago, which increased substantially during the Late Holocene. This same ancestry arrived in Northwest Patagonia by at least 600 years ago, and it co-existed with individuals carrying a southern Andean genetic profile until colonial times. Genetic structure differentiates populations along the Parana River Delta and the Lower Uruguay River by approximately 1,600 years ago. In contrast, individuals from the eastern lowlands of Uruguay show genetic links with Sambaqui-associated populations from the southern coast of Brazil, suggesting the role of human dispersals in connecting tropical lowland cultural traditions. Overall, our work documents the diffusion of genetically distinct groups across all regions studied and provides compelling evidence that large-scale human movements contributed to the remarkable cultural diversity of central Southern Cone populations during the Middle and Late Holocene.

genetics↗