Nasal Gracilization in Sri Lankan Indigenous Vedda: Phenotypic Plasticity and Evolutionary Continuity

The nasal complex, a climatically sensitive trait, offers insight into both long-term adaptation and short-term phenotypic plasticity. We test whether nasal morphology exhibits plasticity parallel to postcranial gracilization in response to subsistence shifts, using Sri Lanka's Indigenous Vedda as a model population. They represent a unique lineage with deep evolutionary continuity to the island's prehistoric inhabitants. While genetic studies affirm their deep ancestry, no systematic data exist on their nasal morphology-making this the first study of its kind in Sri Lanka.

Nasal height and breadth were measured in 328 Vedda adults (≥ 19 years) of confirmed Indigenous ancestry from Yakkure (minimal displacement, 6 km) and Henanigala (resettled 38 km). Nasal index was calculated, and group comparisons used t-tests with age stratification.

Significant sexual dimorphism was observed in groups (p < 0.05). Yakkure adults exhibited larger nasal dimensions (height: 47.59 ± 3.34 mm; breadth: 37.38 ± 2.84 mm) than Henanigala adults (height: 46.55 ± 3.05 mm; breadth: 36.98 ± 2.75 mm), yet Nasal Indices were statistically indistinguishable (Yakkure: 79.69 ± 7.26, Henanigala: 79.20 ± 7.85), with both groups predominantly mesorrhine (67.7%).

This dissociation between size reduction and shape conservation parallels systemic skeletal gracilization, suggesting phenotypic plasticity. The pattern is consistent with Henanigala's environmental disruption and reduced masticatory strain from softer agricultural diets; Yakkure's morphology reflects greater ecological continuity. Comparison with early 20th century data reveals a secular trend toward gracilization and nasal broadening. These findings extend loading-related plasticity to the craniofacial skeleton, illustrating how nasal morphology may encode deep ancestral heritage and plastic responses to rapid biocultural change.