Abstract
The kin selection theory suggests that individuals more likely invest in individuals to whom they are more genetically related. Many studies showed that matrilineal family members may invest more than patrilineal, which is could be explained by connection to the paternity uncertainty.
The grandparents are more certain of the biological relation with their daughters' children (than with their sons') and are expected to invest in them more, which could cause the distinction in perception between matrilineal and patrilineal family members from the respondents. In the present research, we focused on the effect of the kinship rate of various family members on appraisal of representative personal quality - the kindness.
We collected data using an internet questionnaire and recruited respondents through a pool of research volunteers, Facebook and newspapers. The survey contained various socioeconomic, demographic and psychological data related questions aiming mainly on inquiry of prejudice and superstition thinking.
It resulted in obtaining data from 4914 respondents (2044 men, mean age 28.3; 2571 women, mean age 28.0). The respondents rated various family members (and step members) in the dimension of kindness ("this member is more/less kind than other people in general") on a scale 0-5.
Analysis of covariance (ANCOVA) with age of respondents as a covariate showed, that the respondents rated as the "kindest" family member their mother (the average was 3.64) followed closely by matrilineal grandmother (3.59; p<0.001). The next in the rating were the matrilineal grandfather (3.45), the patrilineal grandmother (3.37) and the father (3.37).
They were followed by the patrilineal grandfather (3.26). All the siblings were rated worse than parents and grandparents in general and the average rating for the siblings was 3.05.
We used various family step-members as a control group - there average rating was 2.62-2.71. No significant differences in the ratings were found, if the respondent's gender was taken into account.
In an agreement with the theory of paternity uncertainty, our results showed that the higher is the certainty of biological kinship, the better rating the family member achieved.