Research into third party kinship recognition has been sparse even though kinship provides crucial insight into the biological underpinnings of pro-social and sexual behaviour. Furthermore, the studies that have been conducted are of varying quality and consistency, resulting in a myriad of different findings and conclusions. My doctoral research addressed the common issues in the literature by conducting studies using high quality stimuli, a consistent methodology and appropriate analyses.
Study 1 investigated what facial information is used for making kinship judgments in 3D facial images, specifically the contribution of face shape and surface reflectance information (e.g., skin texture, tone, eye and eyebrow colour). Using binomial logistic mixed models, we found that participants were able to detect relatedness at levels above chance for all three stimulus versions. Overall, both individual shape and surface reflectance information contribute to kinship detection, and both cues are optimally combined when presented together.
Study 2 investigated whether a smiling facial expression increases the accuracy of judging relatedness compared to a neutral facial expression in human raters. Contrary to expectations, smiling decreased the accuracy of relatedness judgments compared to a neutral facial expression.
Study 3 aimed to replicate previous studies suggesting that birth order affects kinship detection ability. Our findings indicate that laterborns do not have an advantage in detecting child sibling pairs and that kinship judgment accuracy is therefore unaffected by rater birth order.
Study 4 compared the performance of participants across three commonly used methods (i.e., kinship judgment, similarity rating, matching paradigm), using the same highly-controlled stimulus set. We found that while responses on all three tasks were correlated, performance varied significantly across the tasks. Furthermore, when looking at the effect sex and age of the portrayed individuals had on performance, we found that different results are found dependent on which method is used
