The spectacular human nose: an amplifier of individual quality?

Abstract

Amplifiers are signals that improve the perception of underlying differences in quality. They are cost free and advantageous to high quality individuals, but disadvantageous to low quality individuals, as poor quality is easier perceived because of the amplifier. For an amplifier to evolve, the average fitness benefit to the high quality individuals should be higher than the average cost for the low quality individuals. The human nose is, compared to the nose of most other primates, extraordinary large, fragile and easily broken-especially in male-male interactions. May it have evolved as an amplifier among high quality individuals, allowing easy assessment of individual quality and influencing the perception of attractiveness? We tested the latter by manipulating the position of the nose tip or, as a control, the mouth in facial pictures and had the pictures rated for attractiveness. Our results show that facial attractiveness failed to be influenced by mouth manipulations. Yet, facial attractiveness increased when the nose tip was artificially centered according to other facial features. Conversely, attractiveness decreased when the nose tip was displaced away from its central position. Our results suggest that our evaluation of attractiveness is clearly sensitive to the centering of the nose tip, possibly because it affects our perception of the face's symmetry and/or averageness. However, whether such centering is related to individual quality remains unclear.

Keywords: Amplifiers; Asymmetry; Attractiveness; Human; Nose; Perception; Signal.

Figure 1. A set of pictures used for attractiveness evaluation.

One set of pictures, in which the right side of the nose and the mouth were used to make the trait symmetric (A) unmanipulated face (B) right symmetric, centered mouth (C) right symmetric mouth, skewed 0.5 cm to the right (D) right symmetric mouth, skewed 1.0 cm to the right (E) right symmetric, centered nose (F) right symmetric nose, nose tip skewed 0.5 cm to the right (G) right symmetric nose, nose tip skewed 1.0 cm to the right.

Figure 2. Result summary.

(A) Dunnett’s 95% confidence intervals for the difference between manipulation levels of Mouth and Nose and the reference level “Unmanipulated”. (B) Box plots of attractiveness ratings for the different manipulations (1 least attractive, 7 most attractive). The uppermost line of the box is the upper (75%) quartile, the lowest line of the box is the lower (25%) quartile and the line in the middle is the median. Box plots are based on average values calculated by orientation.