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

ABSTRACT

Objectives

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.

Materials and Methods

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.

Results

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%).

Discussion

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.

Highlights

• First systematic nasal morphology data for Sri Lanka's indigenous Vedda.

• Nasal gracilization linked to masticatory strain reduction in displaced group.

• Shape conserved despite size change, suggesting phenotypic plasticity.

• Interior‐Coastal Vedda divergence suggests distinct ancestral signals.

1. Introduction

The Vedda, the indigenous people of Sri Lanka, represent one of the most culturally and biologically distinct populations in South Asia. Historically classified as hunter‐gatherers, they have long been of interest to anthropologists seeking to understand human population continuity on the island (P. E. Deraniyagala ¹⁹³⁹; Kennedy ¹⁹⁷¹; Kulathilake ^2016a; Kulathilake ^2016b; Wedage et al. ²⁰¹⁹). Archaeological evidence from Fa Hien Cave, Batadombalena, Belilena, and Bellanbandi Palassa has revealed anatomically modern humans dating from approximately 48,000 to 4800 years ago, with the earliest finds representing some of the oldest such remains in South Asia (S. U. Deraniyagala ¹⁹⁸⁵; S. U. Deraniyagala ^1992a; S. U. Deraniyagala ^1992b; Kennedy et al. ¹⁹⁸⁷). These remains, described by S. U. Deraniyagala (1998) as Homo sapiens balangodensis or “Balangoda Man,” are characterized by robust skeletal traits, prominent brow ridges, large teeth, and relatively short nasal structures; features that persist in varying degrees among contemporary Vedda. Kennedy (1971) demonstrated pronounced biological affinity between prehistoric and modern Vedda skeletons through extensive morphometric comparisons, suggesting long‐standing continuity of hunter‐gatherer morphology on the island. Similarly, Kulatilake et al. (2007) affirmed this continuum, highlighting the Vedda as a population retaining many features of Late Pleistocene and early Holocene inhabitants. Collectively, these studies indicate deep evolutionary ties to prehistoric Sri Lankan humans rather than recent arrival (Kennedy and Deraniyagala 1989; S. U. Deraniyagala ^1992a; S. U. Deraniyagala ^1992b; Kennedy ²⁰⁰⁰).

Genetic studies reinforce these conclusions. Autosomal, Y‐chromosomal, and mitochondrial analyses show that Vedda groups contain genetic elements independent of major later South Asian migrations and share deep ancestry with early Holocene forager populations (Ranaweera et al. 2014). Recent whole‐genome analysis confirms that Vedda retain substantially higher ancient hunter‐gatherer ancestry (52.5%–53.7%) compared to Sinhalese (45.4%–46.9%), directly supporting the continuity hypothesis (Urban Aragon et al. 2025). Independent mitogenomic studies further document population expansion during the microlithic period (~30,000 years ago), linking Vedda demography directly to Balangoda archaeological culture, and reveal high runs of homozygosity indicative of low effective population size and strong genetic drift patterns consistent with long‐term isolation (Welikala et al. 2024). Genetic distance calculations further estimate a divergence time of approximately 50,000 years between Vedda and Sinhalese, corresponding precisely to the period when Homo sapiens balangodensis inhabited Sri Lanka (Ellepola and Wikramanayake 1986). While gene flow with surrounding Sinhalese and Tamil populations has occurred, genetic signatures suggest long‐term isolation and drift rather than recent assimilation (Harihara et al. 1992).

Historically, anthropologists have noted morphological similarities between the Vedda and other South Asian and Southeast Asian foraging populations, including the Kadar and Chenchu of South India and the Andaman Islanders (Wijesekara 1987; S. U. Deraniyagala ^1992a; S. U. Deraniyagala ^1992b; Blundell ²⁰¹²). Such comparisons suggest that the Vedda may preserve traits from multiple waves of early human migration into South Asia, including the southern dispersal route out of Africa (P. E. Deraniyagala ¹⁹³⁹; Kulathilake ²⁰¹³). Geological evidence indicates that Sri Lanka was periodically connected to the Indian subcontinent by land bridges during lowered sea levels, facilitating gene flow and cultural exchange (S. U. Deraniyagala ^1992a; S. U. Deraniyagala ^1992b; Kulathilake ^2016a; Kulathilake ^2016b). Thus, as small, relatively endogamous communities with long‐term occupancy of specific ecological niches, the Vedda preserve phenotypic signatures of both local adaptation and deep evolutionary history. Complementing this evidence, historical and ethnographic sources provide further insight into the ancient distribution of Vedda populations across the island.

The Mahavamsa records (1989) that the Vedda are descended from Prince Vijaya through Kuveni, with their progeny migrating to the region of Sumanakuta (Sri Pada) in the island's wet zone rainforests (Seligman and Seligman 2011). Scholarly evidence, including placenames such as Vedda‐gala and Vedda‐ela in the Ratnapura District and the name Sabaragamuwa itself (“village of forest barbarians”), confirms a significant Vedda presence in these rainforest regions in ancient times (Wijesekara 1987). Over time, with the expansion of agricultural settlements and the growth of Sinhalese and Tamil populations, Vedda communities gradually retreated to the drier interior and eastern regions. This historical displacement was later intensified by large‐scale development programs such as the Gal Oya scheme (1950s) and the Mahaweli Development Project (1980s), which submerged or resettled many remaining traditional settlements.

Given their long‐term occupation of Sri Lanka's interior dry forest and tropical zones including Dambana, Bintenne, and Mahiyanganaya; Vedda nasal morphology is expected to reflect climatic pressures characteristic of hot, seasonal, and often arid environments. These regions experience high daytime temperatures, low humidity, and marked seasonality, all of which exert strong ecogeographic pressures on respiratory morphology. Critically, environmental conditions differ between Vedda subgroups, providing an ideal natural experiment for assessing climate‐related nasal variation and phenotypic plasticity.

The Yakkure community is situated in the Dimbulagala Divisional Secretariat (Polonnaruwa District) within Sri Lanka's historic dry zone, characterized by seasonal monsoons, lower humidity, and dry evergreen forest reflecting the long‐standing ecological niche of many Vedda groups. In contrast, the Henanigala community was resettled from the Uva Province (Dambana/Mahiyanganaya in Badulla District) to the Ampara District in the Eastern Province (Ananda and Nahallage 2022). This relocation represents a significant shift from the island's intermediate zone to the Mahaweli System C zone within Sri Lanka's dry zone landscape fundamentally transformed by large‐scale irrigation and agricultural development under the Mahaweli Project. Thus, the comparison between Yakkure and Henanigala captures not only a contrast between historical continuity and recent displacement but also an ecological transition from a traditional forest‐based habitat to a human‐modified, irrigated agricultural landscape.

Nasal morphology provides a powerful lens through which to examine this interplay between deep ancestry and recent adaptation. Encompassing height, breadth, and shape, the nose reflects a combination of genetic inheritance, climatic adaptation, and long‐term selective pressures (Harrison et al. 1988; Lieberman ²⁰¹¹). As one of the most climatically sensitive craniofacial traits, it exhibits adaptations for respiratory efficiency and thermoregulation. Variation in nasal aperture dimensions correlates strongly with temperature and humidity: populations from cold‐dry climates exhibit features that enhance air warming and humidification, while those from hot‐humid climates display broader, shorter apertures that facilitate airflow and heat dissipation (Noback et al. 2011; Maddux et al. ²⁰¹⁷; Harvati and Weaver ²⁰⁰⁶). This ecogeographic patterning is further evidenced by parallel evolution, where craniofacial form can converge under similar climatic pressures while retaining population‐specific distinctions (Evteev et al. 2024).

Nasal morphology is broadly classified into four types based on the nasal index (breadth/height × 100): Leptorrhine (< 70.0, narrow nose), Mesorrhine (70.0–84.9, medium nose), Platyrrhine (85.0–99.9, broad nose), and Hyperplatyrrhine (≥ 100, very broad nose) (Williams et al. 1995; Porter and Olson ²⁰⁰¹; Oladipo et al. ²⁰⁰⁹). This classification allows for the comparison of Vedda nasal morphology with both regional South Asian populations and globally diverse groups, providing insights into patterns of adaptation, population history, and biological affinity.

Despite this rich interdisciplinary background, systematic data on Vedda nasal morphology remain scarce. Early 20th century surveys, notably by Marett (reported in Stoudt ¹⁹⁶¹), provide a crucial historical benchmark, recording a mean nasal height of 50.31 mm, breadth of 36.96 mm, and a nasal index of 73.93 for Vedda males, suggesting a predominantly mesorrhine to leptorrhine morphology (Stoudt 1961). Sarasin and Sarasin (1886) provided qualitative descriptions of Vedda noses as “very broad” (~40 mm) and “flat,” while Virchow (1881) noted sexual dimorphism in nasal type. However, as Kennedy (1971) and Wikramanayake and Wikramanayake (1992) noted, these early studies were often based on small samples, questionable techniques, or osteological collections of uncertain provenance. As explicitly stated in the literature, “after the work of Stoudt in 1937 comprehensive work on Vedda people's anthropometrical data (on living) have not yet been conducted” (Wikramanayake and Wikramanayake 1992), creating a critical gap for contemporary, systematic somatometric data. Anthropometric data on Sinhalese, Tamil, and Moor populations are also limited to very few studies (Wikramanayake and Gunasekara 1994; Nanayakkara and Chandrasekera ¹⁹⁹⁸). Moreover, the latter study was restricted to children and adolescents below 18 years of age, and recent adult data for these groups remain largely unavailable. Vedda measurements remain limited (Ananda and Nahallage 2024), often outdated, or geographically restricted, with most past studies focusing on cultural practices rather than systematic biological measurement. Consequently, nasal morphology of the Vedda has never been systematically compared across subgroups nor contextualized within South Asian or global climatic patterns.

This gap underscores the need for a systematic morphometric analysis of Vedda nasal structures that tests a specific evolutionary hypothesis. A well‐documented secular trend of skeletal gracilization characterized by reduced bone mass and robusticity has been linked to decreases in biomechanical loading associated with transitions from foraging to agricultural subsistence (Ruff et al. 1993; Trinkaus et al. ¹⁹⁹⁴; Ryan and Shaw ²⁰¹⁵). Phenotypic plasticity, the capacity of a genotype to produce different phenotypes in response to environmental conditions, is increasingly recognized as a key mechanism in human evolution, particularly in craniofacial traits (West‐Eberhard ²⁰⁰³; Lieberman ²⁰¹¹). This study investigates whether similar plastic responses to changes in mobility and environmental loading are detectable in the nasal morphology of the historically distinct Yakkure and Henanigala Vedda populations, thereby extending principles of loading‐related adaptation from the postcranial to the craniofacial skeleton. As shown in the historical baseline data (Table 8) and global comparative framework (Table S4), the Vedda occupy an intermediate nasal position between narrow‐nosed temperate populations and broad‐nosed tropical groups, making them an ideal case study for examining how subsistence transitions and environmental displacement influence nasal morphology. Specifically, we test the hypothesis that nasal morphology in Vedda subgroups reflects their distinct recent histories of ecological continuity versus displacement, leading to differences in absolute size but conservation of proportional shape.

TABLE 8.

Historical and contemporary nasal measurements in Vedda populations.

Population (source)	Era	N	Mean nasal height (mm)	Mean nasal breadth (mm)	Nasal index	Notes
Vedda (Marett/Stoudt 1961)	Early 20th C.	138	50.31 ± 0.31	36.96 ± 0.26	73.93 ± 0.64	Pooled male sample from Anuradhapura & Badulla
Badulla Vedda (Marett/Stoudt 1961)	Early 20th C.	—	49.85	36.77	74.21
Anuradhapura Vedda (Marett/Stoudt 1961)	Early 20th C.	—	52.50	37.85	72.62
Yakkure adults (present study)	21st C.	164	47.59 ± 3.34	37.38 ± 2.84	79.69 ± 7.26	Adults, both sexes
Henanigala adults (present study)	21st C.	164	46.55 ± 3.05	36.98 ± 2.75	79.20 ± 7.85	Adults, both sexes

By examining nasal dimensions, indices, and proportional relationships, this study provides not only a quantitative description of Vedda nasal morphology but also situates these features within broader anthropological, ecological, and evolutionary frameworks. The overarching objective is to elucidate patterns of deep continuity and recent adaptation, thereby assessing the role of phenotypic plasticity versus genetic change in shaping morphological variation. In doing so, this research seeks to contribute to a more nuanced understanding of the Vedda's biological heritage, clarify their affinities with prehistoric Sri Lankan populations, position them within the global context of human craniofacial diversity, and offer new insights into the broader processes shaping human adaptation to environmental change.

2. Materials and Methods

2.1. Study Area and Population History

2.1.1. Henanigala (Resettled Population)

The Henanigala community was formed in the 1980s when indigenous groups from Kandeganvila, Dambana, and Kotabakiniya (Uva Bintenna) were relocated to Henanigala South in Mahaweli System C under the Mahaweli Development Project. This area now falls within the Eastern Province (Ampara District, Dehiathtakandiya Secretariat Division), approximately 38 km from their origin in Mahiyanganaya. The Henanigala South division historically comprised approximately 1930 individuals from 485 families; the current indigenous descendant population is estimated at 1450 individuals (320 families), residing alongside a significant Sinhalese population. Geographically, Henanigala is situated approximately 255 km from Colombo.

2.1.2. Yakkure (Historically Continuous Population)

The Yakkure community is situated in the North Central Province (Polonnaruwa District, Dimbulagala Divisional Secretariat). Affected by the Mahaweli Development Project in 1987, they were relocated from their traditional lands (Parana Yakkure) to their present locality (Pahala Yakkure) a distance of only 6 km, which maintained them within their ancestral ecological zone. Historical records confirm a long‐standing indigenous presence in this locale; they were already established in the region during Seligman's (1908) survey (Seligman and Seligman 2011), though they remained isolated from early anthropological census. The current population of the Pahala Yakkure GN Division is approximately 380 individuals (133 families), residing about 56 km from Kaduruwela and 284 km from Colombo.

2.1.3. Environmental Context

Climate data provide quantitative context for the environmental contrast between the study locations and the original homeland of the Henanigala community. Polonnaruwa District (Yakkure) has a mean annual temperature of approximately 28.6°C, mean annual rainfall of approximately 1600 mm, and a pronounced dry season from June to September, with daytime relative humidity dropping to 50%–53% during the driest months (Department of Meteorology ²⁰²²). Badulla District, where the Henanigala community originally resided in the Dambana/Mahiyanganaya area, has a mean annual temperature of approximately 23.6°C (based on 2014–2021 data) and mean daytime relative humidity of approximately 73% (Department of Meteorology ²⁰²²). The Ampara District (current Henanigala location) has a mean annual temperature of approximately 28°C, mean annual rainfall of approximately 1750 mm, and less seasonal extremes (Centre for Environmental Justice ²⁰²², 15). Nationally, the dry zone (including both Polonnaruwa and Ampara) experiences higher daytime temperatures (average maximum 33°C–35°C) and lower daytime relative humidity (approximately 65%–70%, dropping to ~60% in the driest areas) compared to the wet zone (Department of Census and Statistics ²⁰²²). These climatic differences are significant: the Henanigala community relocated from a cooler upland environment (Badulla, ~23.6°C) to a warmer lowland dry zone (Ampara, ~28°C), a difference of approximately 4°C–5°C, while also experiencing a shift from intermediate to dry zone rainfall patterns and the transformation of the landscape through large‐scale irrigation. These contrasts provide the environmental framework for testing the hypothesis that displacement and subsistence transition influence nasal morphology. However, these climate data represent broad regional averages and may not fully reflect site‐specific microclimates present during the period of anthropometric data collection.

2.2. Sampling Procedure

A purposive sampling strategy was employed to include individuals with confirmed Indigenous ancestry through both matrilineal and patrilineal descent, verified by community leaders and Village Officer's records. Purposive sampling was necessary because some individuals who identify as Vedda have known Sinhalese or Tamil admixture through intermarriage. Including such individuals would introduce genetic confounding, making it difficult to attribute observed nasal differences to displacement and environmental change rather than recent admixture. This approach strengthens internal validity by ensuring that the sampled individuals represent the Indigenous Vedda lineage without recent genetic mixing.

Population information for sample selection was obtained from the respective officers. Although the total sample size for the broader anthropometric study was determined using the Krejcie and Morgan (1970) formula, the present morphometric analysis was restricted to adults aged ≥ 19 years. Individuals below 19 years were excluded to ensure skeletal maturity, reduce measurement variability due to ongoing craniofacial growth, and maintain comparability with adult facial morphology studies previously conducted on these populations. The final adult sample distribution for each community is presented in Table 1.

TABLE 1.

Age and sex distribution of adult participants from Yakkure and Henanigala indigenous populations.

Age group (years)	Yakkure male (n)	Yakkure female (n)	Yakkure total	Henanigala male (n)	Henanigala female (n)	Henanigala total	Grand total
19–29	16	24	40	15	29	44	84
30–39	16	14	30	12	37	49	79
40–49	8	14	22	12	10	22	44
50–59	16	28	44	8	14	22	66
60+	12	16	28	11	16	27	55
Total	68	96	164	58	106	164	328

Note: Bold values indicate sample totals (row and column sums).

2.3. Data Collection

Nasal measurements were collected in accordance with standardized anthropometric protocols (Centers for Disease Control and Prevention [CDC] ²⁰⁰⁹; Bass ¹⁹⁸⁷). Participants were seated with the head oriented in the Frankfurt Horizontal Plane, aligning the tragion and orbitale (Table 2). To ensure precision and rigorous quality control, each nasal dimension was measured twice in succession for every subject using a digital sliding caliper. The final value recorded for analysis was the arithmetic mean of these two readings, rounded to the nearest millimeter. Intra‐observer consistency was quantified using the technical error of measurement (TEM). The calculated TEM for linear dimensions ranged between 0.34 and 0.36 mm, with a relative TEM consistently remaining below 1%. This falls well within the widely accepted reliability threshold of 2% (Perini et al. 2005), confirming the reproducibility of the dataset.

TABLE 2.

Definitions and measurement techniques of nasal dimensions and indices.

Measurement	Definition
Nasal height	Direct distance from nasion to the midpoint of a line connecting the lowest points of the inferior margin of the nasal notches.
Nasal breadth	Maximum breadth of the nasal aperture.
Nasal index	(Nasal breadth/Nasal height) × 100

Note: CDC (2009), Bass (1987), and Porter and Olson (2001).

2.4. Data Analysis

Quantitative data were analyzed using SPSS and Microsoft Excel. Descriptive statistics (mean, minimum, maximum, and standard deviation) were generated for all variables. Parametric comparisons between Yakkure and Henanigala adult populations were conducted using Independent Sample t‐tests. Cohen's d effect sizes were calculated for significant comparisons to assess the magnitude of differences.

2.5. Ethical Approval and Informed Consent

All procedures involving human participants were performed in compliance with the relevant laws and institutional guidelines of Sri Lanka and have been approved by the appropriate institutional Ethics Review Committee (Ref. No. 18/18).

Prior to data collection, informed consent was obtained from all individual adult participants included in the study. The privacy rights of all participants were strictly observed; all data were anonymized during analysis, and personal identifiers were removed from the dataset.

3. Results

The final study sample consisted of 328 adult individuals (≥ 19 years), stratified equally between the Yakkure (n = 164) and Henanigala (n = 164) settlements. The cohort included 126 males (38.4%) and 202 females (61.6%). The mean age was 43.94 ± 15.68 years for Yakkure and 41.23 ± 16.10 years for Henanigala. An independent sample t‐test confirmed that there was no statistically significant difference in the age distribution between the two communities (t = 1.54, p = 0.12). This age matching is critical for the present analysis, ensuring that observed differences in nasal dimensions are attributable to population history rather than age related cartilaginous changes.

3.1. Nasal Dimensions and Sexual Dimorphism

Descriptive statistics for nasal height, breadth, and index are presented in Table 3. Notable sexual dimorphism was observed in both populations, with males exhibiting significantly larger nasal dimensions than females (all p < 0.05, Table 4). In Yakkure, males had higher mean nasal height (49.06 ± 3.26 mm vs. 46.54 ± 3.03 mm) and breadth (39.57 ± 2.81 mm vs. 36.51 ± 2.08 mm) compared to females. A similar pattern was evident in Henanigala, though dimorphism was less pronounced, as reflected in the smaller Cohen's d values (d = 0.35 for nasal height and d = 0.47 for nasal breadth, compared to d = 0.81 and d = 1.27 for Yakkure).

TABLE 3.

Nasal measurements of Yakkure and Henanigala populations (adults aged ≥ 19 years).

Village	Gender	N	Nose height (mm)	Nasal breadth (mm)	Nasal index
			Min–Max (Mean ± SD)	Min–Max (Mean ± SD)	Min–Max (Mean ± SD)
Yakkure	Female	96	41.03–52.65 (46.54 ± 3.03)	31.40–41.03 (36.51 ± 2.08)	63.50–92.00 (78.73 ± 6.32)
	Male	68	41.66–55.00 (49.06 ± 3.26)	30.93–44.73 (39.57 ± 2.81)	57.43–96.24 (81.06 ± 8.26)
Pooled		164	41.03–55.00 (47.60 ± 3.34)	30.93–44.73 (37.89 ± 3.08)	57.43–96.24 (79.64 ± 7.42)
Henanigala	Female	106	40.74–54.39 (46.51 ± 2.96)	29.79–41.99 (36.53 ± 2.75)	63.55–96.13 (78.85 ± 7.60)
	Male	58	40.67–53.00 (47.57 ± 3.12)	32.72–41.54 (37.79 ± 2.57)	67.63–96.14 (79.85 ± 8.31)
Pooled		164	40.67–54.39 (46.88 ± 3.03)	29.79–41.99 (36.90 ± 2.71)	63.55–96.14 (79.14 ± 7.97)
Grand Total		328	40.67–55.00 (47.24 ± 3.18)	29.79–44.73 (37.40 ± 2.91)	57.43–96.24 (79.39 ± 7.70)

Note: Bold values indicate pooled sample summaries (combined male and female) and the grand total.

TABLE 4.

Independent samples t‐test results for population, sex, and cross‐population gender differences in nasal measurements.

Comparison	Group(s)	Measurement	t	df	p	Cohen's d	Interpretation
Population difference	Yakkure vs. Henanigala (all adults)	Nasal height	1.996	326	0.047	0.23	Small effect, Yakkure > Henanigala
		Nasal breadth	2.586	326	0.010	0.34	Small effect, Yakkure > Henanigala
		Nasal index	0.590	326	0.555	0.07	Negligible, not significant
Sex difference (Yakkure)	Yakkure (male–female)	Nasal height	−5.078	162	< 0.001	0.81	Large effect, males >females
		Nasal breadth	−8.007	162	< 0.001	1.27	Very large effect, males>females
		Nasal index	−2.051	162	0.042	0.32	Small effect, males>females
Sex difference (Henanigala)	Henanigala (male–female)	Nasal height	−2.152	162	0.033	0.35	Small‐to‐medium effect, males>females
		Nasal breadth	−2.859	162	0.005	0.47	Medium effect, males>females
		Nasal index	−0.781	162	0.436	0.12	Negligible, not significant
Cross‐population (females)	Yakkure vs. henanigala (females only)	Nasal height	0.093	200	0.926	0.01	Negligible, not significant
		Nasal breadth	−0.077	200	0.938	0.01	Negligible, not significant
		Nasal index	−0.123	200	0.902	0.02	Negligible, not significant
Cross‐population (males)	Yakkure vs. henanigala (males only)	Nasal height	2.613	124	0.010	0.47	Medium effect, Yakkure males>Henanigala males
		Nasal breadth	3.682	124	< 0.001	0.66	Medium‐to‐large effect, Yakkure males>Henanigala males
		Nasal index	0.819	124	0.414	0.15	Negligible, not significant

Note: Bold Cohens d values indicate effect sizes. Cohen's d interpretation: 0.2 = small, 0.5 = medium, 0.8 = large effect (Cohen 1988).

3.2. Inter‐Population Differences

Yakkure adults displayed significantly greater nasal height (t = 1.996, p < 0.047) and nasal breadth (t = 2.586, p < 0.010) than Henanigala adults (Table 4). However, nasal index did not differ significantly between the two groups (t = 0.590, p < 0.555). Cross‐population comparisons stratified by sex revealed that Yakkure males had significantly larger nasal height (t = 2.613, p < 0.010) and breadth (t = 3.682, p < 0.001) than Henanigala males, whereas no significant differences were observed between females of the two communities.

3.3. Age‐Stratified Morphological Variation

Age‐specific analyses revealed nuanced patterns of variation, particularly among males (Table S2). Significant differences in nasal height between Yakkure and Henanigala males were observed in the 30–39 and 40–49 year age groups (p < 0.01). Nasal breadth differed significantly in the 19–29, 50–59, and 60+ year age groups (p < 0.05). Among females, the only significant interpopulation difference was in nasal index within the 50–59 year group (p < 0.039). Detailed age and sex‐stratified descriptive statistics are provided in Table S1.

3.4. Classification of Nasal Morphology

Categorical analysis based on nasal index classified the majority of individuals as mesorrhine (67.7% of total sample), with platyrrhine (21.6%) and leptorrhine (10.7%) morphologies less frequent (Table 5). Mesorrhine predominance was consistent across both sexes and populations, though Yakkure males exhibited a higher frequency of platyrrhine types (38.2%) compared to Yakkure females (8.3%). Age specific distributions revealed that leptorrhine forms were more common in younger adults, whereas platyrrhine morphology increased with age, particularly among Yakkure males aged 60+ (66.7%, Table S3).

TABLE 5.

Nasal index variation by village and gender.

Village	Gender	Leptorrhine (%)	Mesorrhine (%)	Platyrrhine (%)
Yakkure	Female	12.5	79.2	8.3
	Male	8.8	52.9	38.2
	Total	11.0	68.3	20.7
Henanigala	Female	11.3	67.9	20.8
	Male	8.6	65.5	25.9
	Total	10.4	67.1	22.6
Overall population	—	10.7	67.7	21.6

Detailed descriptive statistics by age group (Table S1), age‐specific group comparisons (Table S2), age‐stratified nasal index variation (Table S3), and global comparative data (Table S4) are provided in the Supporting Information.

3.5. Multivariate Analysis of Nasal Dimensions

To assess the combined effects of population (village), sex, and age on nasal morphology, a multivariate analysis of variance (MANOVA) was conducted with nasal height, nasal breadth, and nasal index as dependent variables. All main effects and interactions were included in the model.

Results revealed significant main effects for all three factors (Table 6). Population (village) showed a significant multivariate effect (Pillai's Trace = 0.048, F = 5.135, p = 0.002), indicating that Yakkure and Henanigala differ significantly across the combined nasal dimensions. Sex (Gender) showed a strong multivariate effect (Pillai's Trace = 0.218, F = 28.475, p < 0.001), confirming pronounced sexual dimorphism. Age group also showed a significant multivariate effect (Pillai's Trace = 0.118, F = 3.157, p < 0.001), indicating age‐related variation in nasal dimensions.

TABLE 6.

Multivariate test results (Pillai's trace) for nasal dimensions.

Effect	Pillai's trace	F	Hypothesis df	Error df	p
Intercept	0.998	50964.762	3	306	< 0.001
Village (population)	0.048	5.135	3	306	0.002
Gender (sex)	0.218	28.475	3	306	< 0.001
Age (age group)	0.118	3.157	12	924	< 0.001
Village × gender	0.068	7.438	3	306	< 0.001
Village × age	0.085	2.251	12	924	0.008
Gender × age	0.095	2.531	12	924	0.003
Village × gender × age	0.166	4.513	12	924	< 0.001

Note: Bold p‐values indicate statistically significant effects (p < 0.05). All tests used Pillai's Trace criterion. Exact statistics are reported.

Several interaction effects were also significant. The Village × Gender interaction (Pillai's Trace = 0.068, F = 7.438, p < 0.001) indicates that the magnitude of sexual dimorphism differs between Yakkure and Henanigala. The Village × Age interaction (Pillai's Trace = 0.085, F = 2.251, p = 0.008) and the Gender × Age interaction (Pillai's Trace = 0.095, F = 2.531, p = 0.003) were also significant. The three‐way Village × Gender × Age interaction was significant (Pillai's Trace = 0.166, F = 4.513, p < 0.001), suggesting that the combined effects of population, sex, and age on nasal dimensions are complex and non‐additive.

Follow‐up univariate tests (Table 7) provide specific insights into each dependent variable. Nasal height was significantly influenced by population (F = 4.851, p = 0.028), sex (F = 32.321, p < 0.001), and the village × gender interaction (F = 4.567, p = 0.033). Age group approached but did not reach significance (p = 0.068). The model explained approximately 20% of the variance in nasal height (R ² = 0.201).

TABLE 7.

Tests of between‐subjects effects for nasal dimensions.

Source	Dependent variable	Sum of squares	df	Mean square	F	p
Village	Nasal height	42.672	1	42.672	4.851	0.028
	Nasal breadth	32.995	1	32.995	5.535	0.019
	Nasal index	0.224	1	0.224	0.838	0.361
Gender	Nasal height	284.330	1	284.330	32.321	< 0.001
	Nasal breadth	274.456	1	274.456	46.041	< 0.001
	Nasal index	1.419	1	1.419	5.299	0.022
Age	Nasal height	77.788	4	19.447	2.211	0.068
	Nasal breadth	75.590	4	18.898	3.170	0.014
	Nasal index	2.933	4	0.733	2.738	0.029
Village × gender	Nasal height	40.180	1	40.180	4.567	0.033
	Nasal breadth	81.835	1	81.835	13.728	< 0.001
	Nasal index	1.241	1	1.241	4.633	0.032
Village × age	Nasal height	65.703	4	16.426	1.867	0.116
	Nasal breadth	47.918	4	11.979	2.010	0.093
	Nasal index	4.033	4	1.008	3.764	0.005
Gender × age	Nasal height	107.686	4	26.921	3.060	0.017
	Nasal breadth	63.627	4	15.907	2.668	0.032
	Nasal index	3.620	4	0.905	3.380	0.010
Village × gender × age	Nasal height	105.185	4	26.296	2.989	0.019
	Nasal breadth	76.109	4	19.027	3.192	0.014
	Nasal index	6.925	4	1.731	6.464	< 0.001

Note: Bold values indicate statistical significance at p < 0.05. R ² = 0.201 for nasal height, 0.294 for nasal breadth, 0.192 for nasal index.

Nasal breadth was significantly influenced by population (F = 5.535, p = 0.019), sex (F = 46.041, p < 0.001), age group (F = 3.170, p = 0.014), and the village × gender interaction (F = 13.728, p < 0.001). The model explained approximately 29% of the variance in nasal breadth (R ² = 0.294).

Nasal index showed no significant main effect of population (p = 0.361), confirming the t‐test finding that shape is conserved between Yakkure and Henanigala. However, nasal index was significantly influenced by sex (F = 5.299, p = 0.022), age group (F = 2.738, p = 0.029), and the village × gender (F = 4.633, p = 0.032), village × age (F = 3.764, p = 0.005), Gender × Age (F = 3.380, p = 0.010), and three‐way (F = 6.464, p < 0.001) interactions. The model explained approximately 19% of the variance in nasal index (R ² = 0.192).

These multivariate results confirm and extend the univariate t‐test findings: (1) population and sex independently influence absolute nasal dimensions, (2) nasal shape (as measured by the nasal index) is conserved between populations despite size differences, and (3) complex interactions among population, sex, and age suggest that phenotypic plasticity operates differently across demographic subgroups, with the most pronounced differences observed in specific age and sex categories. However, a stable nasal index—a one‐dimensional ratio of breadth to height—does not preclude more nuanced geometric alterations in the nasal complex. A geometric morphometric approach would be required to confirm full shape conservation. It is important to note, however, that while these multivariate effects are statistically significant, the effect sizes are modest (Pillai's Trace = 0.048 for population), indicating that population explains only a small proportion of the overall variance in nasal dimensions.

4. Discussion

This study provides the first integrated, population‐level analysis of nasal morphology among the Yakkure and Henanigala Vedda, documenting patterns of variation that reflect both deep evolutionary continuity and recent plastic adaptation. It tested the evolutionary hypothesis that the nasal complex, like the postcranial skeleton, exhibits phenotypic plasticity in response to changes in subsistence and biomechanical loading (Ruff et al. 1993; Trinkaus et al. ¹⁹⁹⁴; Ryan and Shaw ²⁰¹⁵). By examining nasal dimensions across adult males and females (aged > 19 years), the findings illuminate the interplay of deep evolutionary continuity and recent plastic adaptation, situating Vedda nasal traits within their environmental context, population history, and broader anthropological patterns.

4.1. Sexual Dimorphism in Adult Nasal Morphology

The study demonstrates clear sexual dimorphism in adult nasal morphology, consistent with global anthropometric trends (Weiner and Lourie 1981; Porter and Olson ²⁰⁰¹; Mukherjee et al. ²⁰²²). Adult males, particularly from Yakkure, exhibited significantly larger nasal height and breadth compared to females. Specifically, Yakkure males recorded a mean nasal height of 49.06 ± 3.24 mm compared to 46.54 ± 3.02 mm in females, while Henanigala males (47.57 ± 3.12 mm) similarly exceeded females (46.51 ± 2.96 mm). These patterns indicate that sexual dimorphism in nasal morphology is a robust, canalized feature in adulthood, corresponding to known hormonal and developmental processes where male craniofacial growth trajectories are extended due to androgenic influence (Enlow 1990; Bhandari et al. ²⁰²¹). This finding contrasts with some early qualitative observations (e.g., Virchow ¹⁸⁸¹, who suggested sharper sexual dimorphism in nasal type) but aligns with broader global trends of males exhibiting larger absolute dimensions.

While these differences are statistically significant, the absolute magnitude of sexual dimorphism is modest approximately 2.5 mm in nasal height and 3.0 mm in nasal breadth for Yakkure, with even smaller differences in Henanigala. To quantify the practical significance of these differences, Cohen's d effect sizes were calculated. For Yakkure, effect sizes were d = 0.81 for nasal height and d = 1.27 for nasal breadth, indicating moderate to large effects. For Henanigala, effect sizes were d = 0.35 for nasal height and d = 0.47 for nasal breadth, indicating small to moderate effects. Thus, while sexual dimorphism is present in both populations, its magnitude is substantially larger in the historically continuous Yakkure community than in the resettled Henanigala community. Statistical significance should not be equated with biological importance; the modest millimeter differences observed here align with global patterns of craniofacial sexual dimorphism. Furthermore, the high statistical power produced by the sample size (N = 328) allows for the detection of relatively small effect sizes. While the population‐level differences are statistically significant, the corresponding Cohen's d values (≈0.23 for nasal height and ≈0.34 for nasal breadth) fall within the small effect range, indicating that these differences should not be interpreted as substantial morphological shifts.

In contrast to the modest population effects, the MANOVA results further confirm the strong effect of sex on nasal dimensions (Pillai's Trace = 0.218, F = 28.475, p < 0.001). The significant village × gender interaction (Pillai's Trace = 0.068, p < 0.001) is consistent with the larger effect sizes observed in Yakkure compared to Henanigala.

4.2. Inter‐Population Variation: The Impact of Resettlement History

A critical finding of this study is the dissociation between absolute nasal dimensions and proportional nasal shape when comparing the two communities. While Yakkure adults exhibited significantly larger nasal dimensions than the Henanigala population (p < 0.05), their Nasal Indices remained statistically indistinguishable (p > 0.05). The population differences in absolute dimensions, while statistically significant, represent a subtle morphological signal (Cohen's d≈0.23–0.34) rather than a large‐scale shift in nasal morphology.

This morphological divergence correlates strongly with the distinct demographic and settlement histories of the two groups and likely reflects differential exposure to environmental and lifestyle changes. The Yakkure community represents a population with high ecological continuity. Historically situated in the North Central Province (Polonnaruwa District), they were relocated only 6 km from their traditional lands (Parana Yakkure) to their present location (Pahala Yakkure) in 1987. Historical records indicate their long‐standing presence in this distinct ecological niche, predating even Seligman's (1908) survey. This regional stability likely allowed them to maintain traditional subsistence behaviors and dietary loads, sustaining a degree of craniofacial robustness.

In contrast, the Henanigala community represents a population defined by displacement and lifestyle transition. Originally inhabiting the Uva Bintenna region (Kandeganvila and Dambana), they practiced circular migration associated with shifting chena cultivation before being permanently resettled in the Eastern Province (Mahaweli System C) in the 1980s, a substantial geographical and ecological shift. The reduced nasal dimensions in Henanigala are statistically consistent with phenotypic plasticity in response to environmental disruption and lifestyle transition, though the modest effect sizes caution against overinterpreting the magnitude of this response. While genetic drift or subtle selection cannot be ruled out in these small populations, the rapid timeline and direction of change align most parsimoniously with plastic responses documented in other populations undergoing similar subsistence shifts (Lieberman 2011; von Cramon‐Taubadel ²⁰¹⁴; Katz et al. ²⁰¹⁷).

Thus, the larger nasal dimensions in Yakkure may reflect the retention of ancestral robusticity due to historical stasis, while the reduced dimensions in Henanigala could signal morphological adjustment to environmental and lifestyle change. However, the stability of the mesorrhine shape across both groups suggests a shared, underlying morphological blueprint that persists despite these disparate recent histories.

Crucially, the observed pattern of size reduction in Henanigala makes extensive recent admixture with neighboring Sinhalese populations an unlikely sole explanation. Historical anthropometric data indicate that Sinhalese and Tamil populations possess significantly larger nasal dimensions (mean nasal height: 51.7 mm; Stoudt ¹⁹⁶¹). If substantial gene flow were the primary driver of change, a shift toward these larger dimensions might be expected. This interpretation is further supported by genetic studies that have consistently shown the Vedda to be genetically distinct from neighboring Sinhalese and Tamil groups, with mitochondrial DNA and autosomal markers indicating long‐term isolation and genetic drift rather than recent assimilation (Harihara et al. 1992; Ranaweera et al. ²⁰¹⁴). Instead, the observed reduction supports phenotypic plasticity as a key explanatory mechanism. This effect is most visible in the oldest group: Yakkure males aged 60+ retain a robust morphology (mean nasal index: 83.66), whereas their Henanigala counterparts show a more gracilized form (mean nasal index: 77.37), illustrating how environmental disruption has impacted even the older generation in the resettled community.

Notably, while Yakkure males exhibited significantly larger nasal dimensions than Henanigala males, no significant differences were observed between females of the two communities for any nasal dimension. This sex‐specific pattern suggests that the plastic response to displacement and subsistence change may be more pronounced in males, potentially due to sex differences in craniofacial growth trajectories, activity patterns, or exposure to environmental stressors. Alternatively, the absence of female differences may reflect the smaller male sample size achieving statistical significance while female similarity represents true biological equivalence. Regardless, this finding qualifies the strength of the overall inter‐population comparison and indicates that the hypothesis of differential plasticity between Yakkure and Henanigala is supported primarily by male data.

The observed pattern of reduced nasal dimensions in Henanigala parallels a well‐established trend of systemic skeletal gracilization in human populations undergoing similar subsistence transitions. However, because we lack controls for overall craniofacial or body size, we refer to this pattern as one that ‘parallels’ documented gracilization trends rather than confirming gracilization as a directly demonstrated process. Research on trabecular bone microstructure has demonstrated that mobile foragers retain a robust, primate‐like skeletal structure, while sedentary agriculturalists exhibit significant reductions in bone strength, a difference attributed primarily to decreased biomechanical loading rather than genetic change (Ryan and Shaw 2015). By analogy, the morphological divergence between the historically stable Yakkure and the resettled Henanigala may reflect a subtle plastic response in the craniofacial complex, consistent with patterns observed in other populations undergoing subsistence transitions. The conservation of the nasal index amidst changes in absolute size further suggests proportional stability, though a stable index does not preclude nuanced geometric alterations in the nasal complex.

The observed reduction in nasal dimensions in Henanigala is consistent with the masticatory‐functional hypothesis, offering a plausible functional interpretation of the observed trends. This hypothesis posits that craniofacial robusticity is maintained, in part, by the magnitude and repetition of strains generated during chewing (Carlson and van Gerven ¹⁹⁷⁷; Lieberman ²⁰¹¹). The traditional Vedda subsistence economy, rooted in hunting and gathering, involved the consumption of mechanically demanding foods: lean game meats requiring significant shearing, fibrous tubers and yams, and hard nuts. These foods generate high‐magnitude strains across the facial skeleton during mastication, which may contribute to bone deposition and the maintenance of robusticity (Carlson and van Gerven ¹⁹⁷⁷). The transition to chena cultivation introduced cooked cereals and legumes, likely representing an initial reduction in dietary mechanical properties. However, the subsequent shift to permanent, irrigated agriculture in the Henanigala resettlement zone with diets becoming dominated by soft, processed carbohydrates (e.g., rice and dairy) likely accelerated this trend, representing a dramatic reduction in masticatory strain. This marked reduction in masticatory loading during growth and development is a well‐documented driver of craniofacial gracilization in bioarchaeological contexts (Carlson and van Gerven ¹⁹⁷⁷; Larsen ¹⁹⁹⁵; Katz et al. ²⁰¹⁷). The smaller absolute nasal dimensions in Henanigala are therefore consistent with a systemic reduction in facial robusticity resulting from decreased masticatory strain, a plastic response, appears to preserve overall nasal shape (Katz et al. 2017), that is superimposed upon their shared Vedda genetic heritage. However, direct proxies for masticatory strain such as dietary hardness, muscle attachment sites, or bone microstructure were not evaluated in this study. This interpretation should therefore be regarded as a plausible, yet untested, functional hypothesis consistent with our findings rather than conclusive evidence of a causal mechanism and should be understood as a morphological analogy to gracilization patterns observed in other bioarchaeological contexts, given that we did not directly measure bone mass, density, or body size.

The MANOVA results confirm that population has a significant multivariate effect on nasal dimensions (Pillai's Trace = 0.048, p = 0.002) even when controlling for sex and age. However, the univariate tests show that this effect is driven by nasal height and breadth, not nasal index (p = 0.361), supporting the hypothesis of proportional shape conservation as measured by the nasal index amidst size variation. A geometric morphometric approach would be required to verify whether full shape conservation extends beyond this proportional measure. The significant three‐way interaction (Village × Gender × Age, Pillai's Trace = 0.166, p < 0.001) further indicates that phenotypic plasticity may operates differently across demographic subgroups, though the modest effect sizes warrant cautious interpretation.

Regarding the age‐specific patterns, the MANOVA results confirm a significant overall Age effect (Pillai's Trace = 0.118, p < 0.001) and a significant three‐way interaction (Village × Gender × Age, p < 0.001), indicating that age‐related nasal variation is complex and non‐uniform across demographic subgroups. The observation that not all male age categories showed significant inter‐population differences may reflect the smaller sample sizes in certain age strata (e.g., Yakkure males aged 40–49, n = 8; Henanigala males aged 50–59, n = 8), which reduces statistical power to detect differences. Additionally, craniofacial growth continues into early adulthood, and age‐related changes in nasal cartilage may contribute to variation in older groups. These factors, combined with sampling variability, likely explain why significant differences are concentrated in specific age groups rather than uniformly across all ages.

4.3. Historical Comparisons and the Secular Trend of Gracilization

When viewed against historical baseline data, a clear secular trend of gracilization and proportional change emerges. Early 20th century surveys, such as those by Marett (reported in Stoudt ¹⁹⁶¹), provide a crucial historical benchmark with precise metrics (Table 8). The comparison reveals a significant morphological shift over approximately 60 years. Contemporary populations show a reduction of approximately 2.7–4.0 mm in Nasal Height but only a marginal increase of 0.3–0.4 mm in Nasal Breadth. This differential change results in a substantial increase of approximately 5.3–6.0 points in the Nasal Index, moving from a historical leptorrhine‐mesorrhine boundary (Nasal Index ~74) to a clear mesorrhine profile (Nasal Index ~79–81). This pattern aligns with Franciscus and Long's (1991) observation that nasal breadth can contribute significantly to nasal index variation, challenging earlier views that nasal height dominates global nasal morphology differences. In the Vedda, both dimensions appear responsive, but height shows greater magnitude of change, consistent with its higher global variability, while breadth changes subtly but meaningfully in shaping the overall index. This suggests not merely gracilization (size reduction) but a proportional broadening of the nose relative to its height, a shift that may reflect changing functional demands or developmental influences associated with sedentary lifeways.

This gradient of reduction is consistent with the relaxation of biomechanical and selective pressures associated with subsistence transition. The correlation between degree of sedentism/resettlement and magnitude of size reduction suggests that lifestyle factors have likely contributed to this morphological trend. As populations transition to agriculture and processed diets, the robust skeletal traits described in prehistoric “Balangoda Man” and early Vedda cohorts (S. U. Deraniyagala ^1992a; S. U. Deraniyagala ^1992b; Kennedy ¹⁹⁷¹) may undergo gracilization, a phenomenon documented globally following subsistence transitions (von Cramon‐Taubadel ²⁰¹⁴; Katz et al. ²⁰¹⁷). The observed nasal broadening further aligns with potential climatic adaptation or developmental responses to changed respiratory patterns. While nasal height is often more variable globally, changes in nasal breadth, as seen in the Vedda's increased nasal index, can reflect functional adaptation to warmer, more humid environments (Franciscus and Long 1991; Noback et al. ²⁰¹¹).

Marett's survey further documented regional variation, with Badulla Vedda and Anuradhapura Vedda both recording mean nasal heights exceeding 50 mm. The reduction observed in Yakkure descended from populations historically near the Anuradhapura region indicates that gracilization may be a widespread trend among Vedda groups, not limited to those experiencing major displacement. However, the more pronounced reduction in Henanigala, whose ancestors share affinities with the Badulla/Bintenna groups, reinforces the interpretation that the combination of long‐distance displacement and accelerated sedentism can amplify morphological change beyond the baseline secular trend.

The observed increase in nasal index from historical (~74) to contemporary Vedda (~79–81) may reflect a combination of plastic responses to lifestyle change and subtle climatic adaptation within warmer, more humid resettlement zones. This aligns with recent findings of parallel craniofacial adaptation in native populations across continents, where nasal morphology shifts predictably with climate yet retains population‐specific signatures (Evteev et al. 2024).

4.4. Regional and Global Context: The Distinctiveness of the Interior Vedda

Having established this pattern of change within the Vedda over time, we now situate the contemporary phenotype of the Yakkure and Henanigala populations within the broader landscape of global human nasal diversity. This comparison clarifies their evolutionary affinities and adaptive profile (A detailed comparative table is provided in Table S4).

The predominantly mesorrhine nasal index of the Vedda aligns with their tropical ecology and is consistent with global trends where broader nasal apertures are found in warmer, more humid climates (Noback et al. 2011; Zaidi et al. ²⁰¹⁷). Our analysis reveals a crucial distinction between the Interior Vedda (Yakkure/Henanigala) and other regional groups, positioning them within a global morphometric range. Historically, anthropologists have noted morphological similarities between the Vedda and other South Asian and Southeast Asian foraging populations, including the Kadar and Chenchu of South India and the Andaman Islanders (Wijesekara 1987; S. U. Deraniyagala ^1992a; S. U. Deraniyagala ^1992b; Blundell ²⁰¹²). While Sarasin and Sarasin (1886) qualitatively described the Vedda as Platyrrhine (“very broad” ~40 mm), our quantitative data classify the modern Interior Vedda as predominantly Mesorrhine (medium nosed), with indices clustering around 79–81. This suggests a refinement of these historical classifications and underscores the value of precise metric analysis over qualitative description. This intermediate nasal index aligns closely with other tropical populations, such as the mesorrhine Malay of Southeast Asia (Nasal Index 76.7/74.6; Than et al. ²⁰¹⁸) and the Akan of West Africa (Nasal Index 82.6/81.5; Appiah et al. ²⁰²³), while remaining distinct from narrower North Indian and broader Coastal Vedda morphologies.

This stands in sharp contrast to the Coastal Vedda populations of Sri Lanka. Recent data (Liyanage et al. 2024) indicate that Coastal Vedda exhibit clear Platyrrhine dominance, with significantly higher indices (Males: 94.58 ± 14.06; Females: 93.93 ± 12.23). This marked difference spanning nearly 15 nasal index points from the interior groups is unlikely to result entirely from recent plasticity. Rather, it likely reflects distinct population histories, differing ancestral signatures, or long‐term adaptation to contrasting coastal versus interior ecologies. The Coastal Vedda's extreme platyrrhine index aligns more closely with Andamanese (Nasal Index ~87–90; Pandey ²⁰⁰⁶) and certain tropical Southeast Asian populations, while the Interior Vedda's mesorrhine profile resembles South Indian tribal groups and the mesorrhine populations of mainland South Asia (Nasir et al. 2021).

This intra‐island variation raises the possibility that Sri Lanka's indigenous populations may not represent a single, homogeneous biological entity but rather preserve distinct ancestral signals from different prehistoric migration events. Such a hypothesis aligns with genetic evidence for deep ancestry in the Vedda (Ranaweera et al. 2014) but suggests that subsequent isolation and drift or differential admixture may have expanded these differences. Further integrated genetic and phenotypic research would be needed to disentangle these possibilities.

Globally, the Interior Vedda occupy a unique intermediate position. They are markedly narrower than hyper‐platyrrhine African populations such as the Ijaws of Nigeria (Nasal Index≈99.83; Oladipo et al. ²⁰¹⁰) and the Andamanese Onges (Nasal Index≈87–90; Pandey ²⁰⁰⁶). Conversely, they are consistently broader than the predominantly leptorrhine populations of North India (e.g., pooled Indian Nasal Index 73.1/72.9; Nasir et al. ²⁰²¹; North Indian general ~66.4; Mehta and Srivastava ²⁰¹⁷) and the leptorrhine South Indian sample reported by Radha and Srinivasan (2019; Nasal Index ~66), underscoring their distinct tropical adaptation. Their historical Nasal Index of ~74 (Stoudt 1961) aligns more closely with these North Indian values, highlighting the significant proportional shift over time. This shift mirrors a documented pattern of skeletal gracilization, here expressed in the craniofacial skeleton (Ryan and Shaw 2015). While deep ancestral links to South Asian populations exist, the Vedda have followed a distinct adaptive or plastic trajectory, resulting in a nasal morphology substantially broader than many contemporary South Indian populations, a pattern likely shaped by differing subsistence histories, local microclimates, and the preservation of ancestral tropical adaptations.

At the same time, the mesorrhine index (~79–81) is consistent with global trends where populations from warm humid climates exhibit broader nasal apertures (Noback et al. 2011), reflecting adaptation to Sri Lanka's tropical ecology. Our findings refine this understanding by demonstrating that despite centuries of contact and gene flow with Sinhalese and Tamil populations, the fundamental nasal proportions have shifted significantly from historical baselines (from ~74 to ~79–81), with the Nasal Index showing greater plasticity than previously recognized. The conserved mesorrhine shape across contemporary subgroups, however, suggests a retained morphological signature distinct from their Sinhalese and Tamil neighbors, one that reflects both ancestral heritage and persistent adaptation to a tropical environment.

Globally, the Vedda occupy an intermediate nasal position that reflects both deep tropical ancestry and possible recent climatic influences. Recent research shows that while nasal morphology can evolve in parallel in response to climate, regional differences in nasal breadth persist due to distinct evolutionary histories (Evteev et al. 2024). The Vedda's intermediate nasal index may therefore represent a trade‐off between ancestral morphology and adaptive plasticity within Sri Lanka's tropical environment.

The global cline from hyper‐platyrrhine to leptorrhine extremes underscores the broader evolutionary significance of the Vedda nasal phenotype. Their intermediate position reflects a dual heritage: a deep ancestral morphology adapted to tropical environments, subsequently modified by gracilization linked to subsistence change. This pattern reinforces the principle that modern human craniofacial diversity results from the interplay of long‐term climatic adaptation and more recent, plastic responses to shifting lifeways.

It is important to acknowledge, however, that the global comparison reveals considerable overlap in nasal indices across different climate zones. For example, Malay students (Nasal Index 76.7/74.6) occupy a tropical/humid environment yet exhibit nasal indices similar to the mesorrhine Vedda rather than the broader platyrrhine morphology predicted by strict ecogeographic models. This overlap suggests that while broad trends in nasal dimensions correlate with climate, finer distinctions such as those between tropical/dry and tropical/humid zones cannot be reliably distinguished using external nasal measurements alone. Factors such as population history, genetic drift, and subsistence‐related plasticity may confound climate‐driven patterns at smaller geographic scales. Thus, the climatic interpretation offered here is presented as one of several possible explanations for the observed variation.

4.5. Environmental Adaptation

The observed morphology aligns with broad ecogeographic expectations. Broad noses are functionally advantageous in warm, humid climates, facilitating heat and moisture exchange, while narrower noses are selected in colder, drier environments (Franciscus and Long 1991; Noback et al. ²⁰¹¹). The persistence of a mesorrhine‐to‐platyrrhine nasal index in the modern Vedda corresponds to their long‐term occupation of Sri Lanka's tropical zones. However, the specific environmental contrast between the study populations adds nuance to this pattern.

The Yakkure community resides within Sri Lanka's historic dry zone (Polonnaruwa District), characterized by seasonal aridity and dry evergreen forest. Quantitative climate data confirm that Polonnaruwa has a pronounced dry season (June rainfall as low as 28 mm, daytime humidity dropping to 50%–53%), while Ampara receives higher annual rainfall (~1750 mm vs. ~1600 mm) with less seasonal extremes (Department of Meteorology ²⁰²²; Centre for Environmental Justice ²⁰²²). In contrast, the Henanigala community, while also situated within the dry zone, occupies the Mahaweli System C Zone—a landscape fundamentally transformed by large‐scale irrigation and agricultural development. This transformation has created a human‐modified environment distinct from the traditional forest‐based habitat, with year‐round water availability and intensive rice cultivation. Under strict ecogeographic models, a shift to a more consistently moist micro‐environment might predict nasal broadening. Yet, nasal index remained stable between groups, while absolute size decreased in the resettled population.

The increase in nasal index from the historical baseline (~74) to contemporary Vedda (~79–81) is therefore more parsimoniously explained by the gracilization process where a reduction in nasal height outpaces any reduction in breadth, potentially amplified by the developmental context of a more sedentary lifestyle. The broader indices in Yakkure males may represent an interaction effect: the retention of greater ancestral robusticity within a plastic framework, upon which ongoing climatic selection pressures could act. This tendency is particularly pronounced in Yakkure males, among whom nasal type distribution shows a greater platyrrhine tendency (38%) compared to Yakkure females (8%), a pattern potentially linked to stronger climatic selection pressures on males engaged in traditional outdoor subsistence activities. Although contemporary Yakkure males now practice cattle farming and paddy cultivation, their recent history of chena cultivation and the deeper ancestral reliance on hunting and gathering within the dry zone forest (Ananda and Nahallage 2022) may have contributed to maintaining selective pressure for respiratory traits suited to that environment. While there is no definitive evidence of climatic selection, this pattern is consistent with broader ecogeographic trends.

Thus, the Vedda nasal complex represents a composite signal: a phylogenetic signature of deep South Asian ancestry, modified by a clear secular trend toward gracilization and proportional broadening, shaped by both lifestyle transitions and persistent climatic adaptation. In particular, the shift from a hunter‐gatherer diet to one based on cooked cereals and, ultimately, soft agricultural products would have reduced the masticatory loads on the developing facial skeleton, contributing to the observed secular trend of size reduction (gracilization). While phenotypic plasticity offers a parsimonious explanation for the rapid changes observed following displacement, the nasal complex also retains signatures of longer‐term climatic selection (Zaidi et al. 2017). The stability of nasal shape despite climatic and lifestyle shifts suggests that plastic responses to reduced loading may have a more immediate morphological impact than climatic selection over this short temporal scale, effectively decoupling recent size changes from underlying ecogeographic adaptations.

In sum, the Vedda nasal phenotype serves as a living archive, encoding signatures of deep Pleistocene ancestry, chronicling a century of rapid subsistence transition, and reflecting persistent adaptation to a tropical ecology. This study establishes nasal morphology as a sensitive, dual‐purpose indicator in bioanthropology, capable of tracking both long‐term evolutionary history and recent biocultural change.

4.6. Study Limitations

While this study provides a comprehensive analysis of nasal morphology in two Vedda communities, several limitations should be acknowledged. First, the cross‐sectional design limits our ability to infer individual‐level changes over time; longitudinal data would be needed to directly track morphological responses to resettlement. Second, despite the overall adequate sample size, certain age and sex subgroups contained smaller numbers, which may reduce statistical power for fine‐grained comparisons within the age‐stratified analyses. Third, historical comparisons rely on early 20th century datasets (e.g., Marett/Stoudt ¹⁹⁶¹) that may differ in measurement protocols, sampling strategies, and demographic composition from our contemporary sample, though they remain the best available baseline. Fourth, while phenotypic plasticity is the most parsimonious explanation for the observed differences, we cannot rule out the potential influence of genetic drift or subtle selection in these small, historically isolated populations. Future studies incorporating longitudinal designs, genomic data, and detailed environmental metrics would help to further disentangle the relative contributions of plasticity, genetics, and local adaptation.

An additional limitation concerns the interpretation of gracility and robusticity. These terms typically refer to relative bone strength or mass, not simply absolute size. The present study uses nasal height and breadth as representations for facial robusticity, but without controlling overall craniofacial or body size, it is possible that the observed differences between Yakkure and Henanigala could be partly accounted for by allometric scaling in addition to true gracilization. Given the absence of controls for overall craniofacial or body size, we cannot definitively distinguish between true gracilization (reduction in relative robusticity) and isometric scaling (proportional size reduction). We therefore interpret “gracilization” as a morphological analogy to patterns documented in other populations undergoing subsistence transitions, rather than a directly demonstrated process. Future studies incorporating cranial base dimensions, facial height, or body mass index would help determine whether the nasal differences observed here are independent of overall size or represent proportional scaling.

While we have incorporated available climate data from official sources (Department of Meteorology ²⁰²²; Centre for Environmental Justice ²⁰²²; Department of Census and Statistics ²⁰²²), these represent broad regional averages rather than site‐specific measurements taken concurrently with anthropometric data. Future studies incorporating direct environmental measurements (temperature, humidity, altitude) at the time of data collection would allow for more rigorous testing of ecogeographic hypotheses.

While the present study includes a broad regional and global comparison of nasal indices (Section 4.4, Table S4), a direct comparison with contemporary Sinhalese or Tamil populations from Sri Lanka using identical measurement protocols was beyond the scope of this study. Available data on comparable age groups are limited, use different measurement techniques, are outdated, and are restricted to few age groups (Wikramanayake and Gunasekara 1994; Nanayakkara and Chandrasekera ¹⁹⁹⁸). Furthermore, the absence of standardized contemporary comparative data from other Sri Lankan ethnic groups complicates determining whether the mesorrhine status observed in the Vedda reflects a unique indigenous feature or a broader regional trend among dry zone populations. Future studies employing standardized protocols across all Sri Lankan ethnic groups and adult age groups would help contextualize the distinctiveness of Vedda nasal morphology.

It is also important to acknowledge that the statistical significance of the population‐level differences is partly attributable to the relatively large sample size (N = 328), which provides high power to detect small effects. While these findings are robust in a statistical sense, the modest effect sizes (Cohen's d≈0.23–0.34; Pillai's Trace = 0.048) indicate that the observed morphological differences between Yakkure and Henanigala are subtle. The results should therefore be interpreted as evidence of a mild, rather than pronounced, morphological signal.

Additionally, while the nasal index provides a useful measure of proportional shape, it is a one‐dimensional ratio that cannot capture more nuanced geometric alterations in the nasal complex. A geometric morphometric approach would be required to confirm full shape conservation beyond the proportional stability observed here.

5. Conclusion

This study presents the first integrated morphometric analysis of adult nasal morphology among the Yakkure and Henanigala Vedda: the indigenous people of Sri Lanka, documenting a pattern of diversity that reflects both deep evolutionary continuity and recent plastic adaptation. By situating contemporary data within a precise demographic and historical framework, the findings reveal a significant secular trend of nasal gracilization: the reduction in nasal dimensions from early 20th century Vedda to present‐day communities mirrors the well‐documented postcranial gracilization observed globally as a plastic response to decreased biomechanical loading.

The divergence between the larger‐nosed Yakkure (historically stable, minimally displaced) and the smaller‐nosed Henanigala (experiencing major displacement and subsistence change) illustrates phenotypic plasticity in the craniofacial complex. MANOVA results confirm that while population significantly affects nasal height and breadth (Pillai's Trace = 0.048, p = 0.002), nasal index remains unaffected (p = 0.361), supporting the hypothesis of shape conservation amidst size variation. This plastic response is likely mediated, in part, by reductions in masticatory loading accompanying the transition from a mechanically demanding hunter‐gatherer diet to softer, cultivated and processed foods, a shift most pronounced in the resettled Henanigala community. The conservation of nasal shape despite changes in absolute size suggests that the Vedda retain a shared morphological blueprint; “shape stasis” alongside size reduction argues against substantial recent admixture and highlights the acculturative environment as a primary driver of phenotypic scaling. This finding underscores how environmental pressures may modulate phenotype without altering underlying genetic architecture.

Furthermore, this research refines the anthropological classification of Sri Lanka's Indigenous people. Contrary to early colonial descriptions of a strict Platyrrhine population, the modern Interior Vedda are predominantly Mesorrhine. This morphology distinguishes them from the Platyrrhine dominant Coastal Vedda and hyper‐platyrrhine African groups, aligning them more closely with deep indigenous lineages of South Asia. The marked divergence between Interior and Coastal Vedda spanning nearly 15 nasal index points raises the possibility that Sri Lanka's indigenous populations may preserve distinct ancestral signals from different prehistoric migration events, a hypothesis warranting further integrated genetic and morphological investigation. Their intermediate nasal index represents a unique adaptive position shaped by deep tropical ancestry and modified by recent gracilization linked to sedentism, dietary softening, and ecological change.

Ultimately, the Yakkure and Henanigala Vedda constitute a unique biological reservoir, preserving craniofacial adaptations that trace to the Late Pleistocene while simultaneously demonstrating the dynamic plasticity of the human skeleton. The Vedda nasal phenotype thus serves as a living archive, encoding signatures of deep evolutionary history and chronicling a century of rapid subsistence transition. This study provides support for extending the principle of loading‐related phenotypic plasticity from the postcranial to the craniofacial skeleton, offering a powerful model for understanding how indigenous phenotypes record the complex interplay of ancestral legacy, genetic continuity, and the immediate biological imprint of societal and environmental change.

Author Contributions

Charmalie Anuradha Dona Nahallage: conceptualization, supervision, writing – original draft, writing – review and editing, methodology. Dissanayakalage Tharaka Harshani Ananda: conceptualization, investigation, writing – original draft, methodology, validation, visualization, writing – review and editing, formal analysis, data curation, resources.

Funding

The authors have nothing to report.

Disclosure

The authors have nothing to report.

Ethics Statement

All procedures involving human participants were performed in compliance with the relevant laws and institutional guidelines of Sri Lanka and were approved by the Ethics Review Committee of the Faculty of Medical Sciences, University of Sri Jayewardenepura (Ref. No. 18/18). Prior to data collection, informed consent was obtained from all individual adult participants included in the study. The privacy rights of all participants were strictly observed; all data were anonymized during analysis, and personal identifiers were removed from the dataset.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Table S1: Descriptive statistics of nasal dimensions by village, gender, and age group (adults ≥ 19 years).

Table S2: Sex‐ and age‐specific differences in nasal morphology.

Table S3: Nasal index variation by village, gender, and age.

Table S4: Comparative nasal morphology in global populations.

Data Availability Statement

The datasets generated and analyzed during this study are not publicly available due to privacy and ethical restrictions related to the identification of participants from small, indigenous communities. However, de‐identified aggregate data supporting the findings are presented within this manuscript (Tables 1, 2, 3, 4, 5, 6, 7, 8) and in the Tables S1–S4. Derived data such as means, standard deviations, and test statistics are fully reported in the results. Requests for further details or collaboration may be directed to the corresponding author subject to ethical approvals and data‐sharing agreements.