Twins Psychology 12 Brothers 7 Mistaken identity 7 Shipwreck survival 6 Brothers and sisters 5 Nature and nurture 5 more ... Research 4 Families 3 Siblings 3 Social aspects 3 Blind women 2 Child psychology 2 Cystic fibrosis 2 Ethnology 2 Family relationships 2 Genetic aspects 2 Genetic psychology 2 Health 2 Infants 2 Mental illness 2 Methodology 2 Multiple birth 2 Multiple pregnancy 2 Patients 2 Shipwreck victims 2 Sibling rivalry 2 Sisters 2 Social ecology 2 Toddlers 2 less ...