Psychologist colin deyoung and his colleagues had over 100 male and female participants undergo mri scans and also take the neo personality inventory, a personality test that is used to measure the big five. the researchers then compared the brain scans and the personality test results. what was one of the results that they found

They found that Agreeableness was associated with greater volume in the fusiform gyrus, an area of the cortex specialized for perceiving faces.
This indicates that people that are more agreeable more nature tend to obtain the characteristic because they're better at identifying small facial expression that might reveal someone's characters.