The Influence of Ethnicity, Sex and Subject on Facial Shape

Objectives: To determine the influence of ethnicity, biological sex and subject on facial shape using 3-level Multilevel Principal Component Analysis (mPCA).
Methods: 3D laser facial scans were captured of 15-32 year old Caucasian English, Welsh, Croatian and Finnish males and females (n=250). 21 landmarks were manually plotted onto scaled grey-scale images. Multilevel PCA assessed ethnicity-, sex-, and subject-level variation individually. These differences were visualised as videos using average faces at 0.1 standard deviation (SD) increments to as many SDs as sample sizes would reasonably allow (+/- 2-3SD).
Results: 1. Ethnicity-level variation: The Croatians were most distinguishable. Differences between the ethnicities were found in all of the main facial features.
2. Sex-level variation: Female faces are shorter and rounder with smaller noses, less prominent brow ridges and shorter upper lips. The Finnish population was the least sexually dimorphic.
3. Subject-level variation: Most of the variation is at this level, therefore most of the differences between the faces are not explained by ethnicity or sex. Facial height, facial profile, inter-canthi width, nasal shape and lip competence describe the largest differences between the subjects.
Conclusions: 1. Ethnicity influences all facial features.
2. Female faces are differentiable from male faces in all ethnicities, however sexual dimorphism was less pronounced in the Finnish population.
3. The majority of the differences in individuals’ faces are not explained by ethnicity or biological sex.
4. Multilevel PCA allows confounding factors to be analysed independently of each other. It provides a tool for exploring the influence of genetic and environmental factors on facial shape, which is the subject of further work.