Human's cognitive ability to assess facial cues from photographs: a study of sexual selection in the Bolivian Amazon.

Eduardo A Undurraga,Thomas W Mcdade,Colleen Nyberg,Tomás Huanca,Ruoxue Wang,William R Leonard,Oyunbileg Magvanjav,Susan Tanner,Taps Bolivia Study Team ,Victòria Reyes-García ,Dan T A Eisenberg ,Ricardo Godoy

doi:10.1371/journal.pone.0011027

Abstract

BackgroundEvolutionary theory suggests that natural selection favors the evolution of cognitive abilities which allow humans to use facial cues to assess traits of others. The use of facial and somatic cues by humans has been studied mainly in western industrialized countries, leaving unanswered whether results are valid across cultures.Methodology/Principal FindingsOur objectives were to test (i) if previous finding about raters' ability to get accurate information about an individual by looking at his facial photograph held in low-income non western rural societies and (ii) whether women and men differ in this ability. To answer the questions we did a study during July-August 2007 among the Tsimane', a native Amazonian society of foragers-farmers in Bolivia. We asked 40 females and 40 males 16–25 years of age to rate four traits in 93 facial photographs of other Tsimane' males. The four traits were based on sexual selection theory, and included health, dominance, knowledge, and sociability. The rating scale for each trait ranged from one (least) to four (most). The average rating for each trait was calculated for each individual in the photograph and regressed against objective measures of the trait from the person in the photograph. We found that (i) female Tsimane' raters were able to assess facial cues related to health, dominance, and knowledge and (ii) male Tsimane' raters were able to assess facial cues related to dominance, knowledge, and sociability.Conclusions/SignificanceOur results support the existence of a human ability to identify objective traits from facial cues, as suggested by evolutionary theory.

Highlights

For it is true that bones and flesh are not enough to constitute a face, (...) and that is why it is infinitely less physical than the body: it is characterized by the look in the eyes, the expression of the mouth, the wrinkles, by all that conjunction of subtle attributes whereby the souls reveals itself by way of the flesh Ernesto Sabato, On Heroes and Tombs. (1961/1981)Evolutionary theory suggests that natural selection favors the evolution of cognitive abilities which allow humans to use facial and other somatic cues to assess traits of other people, such as sex, age, health, or aggressiveness [1,2,3,4,5,6]
The results shown in column [1], row [5.1], Table 3 suggest a significant difference between the way females and males rated the health status of the subject in the photographs
Each additional ailment reported by the subject in the photograph was associated with the subject being rated as having 5.61 percentagepoints worse health by female raters than by male raters (p = 0.01)

Summary

Introduction

Evolutionary theory suggests that natural selection favors the evolution of cognitive abilities which allow humans to use facial and other somatic cues to assess traits of other people, such as sex, age, health, or aggressiveness [1,2,3,4,5,6]. Humans have developed the ability to judge traits in others. Humans have developed the ability to use facial and somatic cues to assess the ability of others to offer physical protection, access to resources, care for the offspring, and generosity [14,15,16,17,18,19,20]. Evolutionary theory suggests that natural selection favors the evolution of cognitive abilities which allow humans to use facial cues to assess traits of others. The use of facial and somatic cues by humans has been studied mainly in western industrialized countries, leaving unanswered whether results are valid across cultures

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Methods

Results

Discussion

Conclusion