DOI: 10.11606/9786587596167 This book is made available under Creative Commons license to allow others to freely access, copy and use provided the authors are correctly attributed. Universidade de São Paulo Reitor – Prof. Dr. Vahan Agopyan Vice-Reitor – Prof. Dr. Antonio Carlos Hernandes Pró-Reitor de Pesquisa – Prof. Dr. Sylvio Roberto Accioly Canuto Pró-Reitor de Pós-Graduação – Prof. Dr. Carlos Gilberto Carlotti Júnior Pró-Reitor de Pós-Graduação – Prof. Dr. Edmund Chada Baracat Pró-Reitora de Cultura e Extensão Universitária – Profa. Dra. Maria Aparecida de Andrade Moreira Machado Instituto de Psicologia Diretora – Profa. Dra. Ana Maria Loffredo Vice-Diretor – Prof. Dr. Gustavo Martineli Massola Departamento de Psicologia Experimental Chefe – Prof. Dr. Marcelo Fernandes Da Costa Vice-Chefe – Prof. Dr. Marcelo Frota Lobato Benvenuti Organizing Committee of the Twin Studies in Behavioral and Health Research: Current Status, Prospects and Applications Profa. Dra. Emma Otta (IPUSP) Profa. Dra. Patrícia Ferreira Monticelli (FFCLRP) Prof. Dr. Claudio Possani (IME-USP) Dra. Tania Kiehl Lucci (IPUSP) Dr. Ricardo Prist (IPUSP) Cover Photo: Tomaz Maranhão Book formatting: Sofia Barbosa Lima English Editing Services: Michael Germain and Lisa Burger, MC TRADUÇÕES S/S LTDA Apoio: Catalogação na publicação Serviço de Biblioteca e Documentação Instituto de Psicologia da Universidade de São Paulo Twin studies in behavioral and health research: current status, prospects and aplications / Organized by Emma Otta e Tania Kiehl Lucci -- São Paulo, Instituto de Psicologia da Universidade de São Paulo, 2021. 170 p. ISBN: 978-65-87596-16-7 DOI: 10.11606/9786587596167 1. Gêmeos. 2. Pesquisa comportamental. 3. Pesquisa em saúde. I. Otta, E., ed. II. Lucci, T. K., ed. III. Título. Ficha elaborada por: Cristiane de Almeida Camara - CRB 5384/08 Contents Foreword i Nancy L. Segal Acknowledgments iii Dedication iv Part A - Laying the Foundation for a Research Program CHAPTER 1: The University of São Paulo Twin Panel: 2 fostering research on twin-related issues from a behavioral perspective Emma Otta and Eloisa de Souza Fernandes CHAPTER 2: The Uruguayan Twins Project: Foundation of a 18 Registry of Uruguayan Twins Sylvia Corte, Valentina Melo, Laura Szteren Part B - Statistical analysis of twin data CHAPTER 3: Mixed models and statistical analysis of twin data 30 Vinicius Frayze David Part C - Subjective Well-Being and Individual Differences CHAPTER 4: Environmental sensitivity and vantage sensitivity 41 Michael Pluess CHAPTER 5: Genetically Informed Family Studies Are Social 52 Science Eric Turkheimer Part D - Psychological Perspective on Twinship Development CHAPTER 6: New Directions in Understanding Twin 62 Relationships Hila Segal and Ariel Knafo-Noam CHAPTER 7: Twin Relationships in Childhood: Effects of 71 Zygosity, Age and Sex Isabella França Ferreira, Tania Kiehl Lucci, Vinicius Frayze David, and Emma Otta CHAPTER 8: Building identity in twins: some reflections 80 Maria Elizabeth Barreto Tavares dos Reis CHAPTER NINE: Mate Preference and Sexual Orientation in 84 Twin Pairs Hellen V. V. Corrêa, Luis C. P. Monteiro, Flávia I. B. Brandão, Nelson C. M., Willian D. Ribeiro, and Ana C. Miranda CHAPTER 10: Twins Reared Apart: History, Findings, Unique 103 Cases and Implications Nancy L. Segal Part E – Health and Well-Being CHAPTER 11: Evaluation of food neophobia in twins 113 Fívia de A. Lopes, Luzia E. A. Martins, Felipe N. Castro CHAPTER 12: Twin pregnancy: challenges to reduce preterm 124 births Maria de Lourdes Brizot CHAPTER 13: Genetic influence on developmental enamel 130 defects Marina de Deus Moura de Lima, Renara N. C. Silva, and Lúcia de F. A. de D. Moura CHAPTER 14: Assessment of Oral Health Outcomes among 138 Twins: The Cardec Twins Initiative Fausto Medeiros Mendes, Julia G. Freitas, Laura Regina A. Pontes, Esperanza A. Martinez-Mier, Juan S. Lara CHAPTER 15: Overview of the Clinical Branch of the 147 University of São Paulo Twin Panel Maria Lívia Tourinho Moretto, Gustavo de Giorgi Ramos Foreword Nancy L. Segal Twin research is expanding at an increasing rate, largely due to evidence of genetic influences on many human characteristics thought to be of mostly environmental origin, such as religiosity and political participation. Methodological advances and statistical refinements have reshaped the classic monozygotic (MZ) - dizygotic (DZ) twin comparison into one of the most informative investigative tools, without detracting from its simplicity and elegance. First of all, I would like to revisit the idea behind the conception of this book. It was inspired by the online conference “Twin Studies in Behavioral and Health Research: Current Status, Prospects and Applications” organized by Emma Otta, Tania Kiehl Lucci and others from the University of São Paulo Twin Panel. The event was held on 11 December 2020 and brought together a group of international presenters and moderators who addressed a diversity of twin-related topics in the behavioral and health sciences. It is a pleasure to introduce the distinguished authors and their chapters on twin studies. The book is divided into five sections that together provide a unifying framework for the different chapters. Part A. Laying the Foundation of a Research Program includes contributions from Emma Otta and Eloisa S. Fernandes of the University of São Paulo Twin Panel; and Sylvia Corte, Laura Szteren and Valentina Melo González of the Uruguayan Twins Project. Otta and Fernandes offer a comprehensive overview of research activities by the University of São Paulo Twin Panel, noting the underrepresentation of twin studies from South America. Corte and colleagues provide an overview of the new registry of Uruguayan twins, developed as part of the Uruguayan Twins Project. Part B. Statistical Analysis of Twin Data, provides an insightful chapter by Vinicius Frayze David of the Institute of Psychology of São Paulo. David defines the genetic components of heritability and describes analyses of twin data via intraclass correlations, mixed models and related procedures. Part C. Subjective Well-Being and Individual Difference, includes chapters by Michael Pluess of the Queen Mary University of London, and Eric Turkheimer of the University of Virginia, Charlottesville. Pluess discusses the nature and mechanisms of environmental and vantage sensitivity in genetic perspective. Turkheimer explores relationships between behavior genetics and twin studies, asserting that behavior genetics is about using the structure of twin genetics to enable inferences about causality in ways that cannot be inferred from ordinary data. Part D. Psychological Perspective on Twinship Development, brought together Hila Segal and Ariel Knafo-Noam of the Hebrew University of Jerusalem, in Israel; Isabella França Ferreira, Tania Kiehl Lucci, Vinicius Frayze David and Emma Otta of the Institute of Psychology of São Paulo; Maria Elizabeth Barreto Tavares dos Reis from the State University of Londrina; Hellen Vivianni V. Corrêa, Luis C. P. Monteiro, Flávia I. B. Brandão, Nelson C. Medrado, Willian D. Ribeiro, Ana C. Miranda of the Federal University of Pará; and Nancy L. Segal from the Twin Studies Center at California State University, Fullerton. H. Segal and Knafo-Noam present new directions in twin relationship research, defining specific dimensions of relatedness, while noting the relative lack of research in this area. Ferreira et al. focus on twin relationships in childhood, noting that MZ twins are closer and more dependent on one another than other pairs, and boys are less close and more conflictual regardless of zygosity. dos Reis examines twins’ identity issues, in particular twins’ early relations with and separation from their mother, and their complex sense of self as both part of and distinct from their twinship. Hellen Vivianni Veloso Corrêa and her colleagues examine mate selection and sexual orientation in MZ and DZ twins from the northern regions of Brazil. Segal surveys findings from past and present reared-apart twin research and presents outcomes from a study of doubly switched-at-birth Colombian twins. Part E. The book concludes with Part E. Health and Well-Being. This section includes contributions from Fivia de Araújo Lopes, Luzia Elionaide Albuquerque Martins and Felipe Nalon Castro of the Federal University of Rio Grande do Norte; Maria de Lourdes Brizot of the University of São Paulo; Marina de Deus Moura de Lima of the Federal University of Piauí; Fausto Medeiros Mendes, Julia Gomes Freitas, and Laura Regina Antunes Pontes the University of São Paulo and Esperanza Angeles Martinez-Miller and Juan Sebastian Lara from the Indiana University School of Dentistry; and Maria Lívia Tourinho Moretto and Gustavo di Giorgi Ramos of the University of São Paulo. Lopes, Martins and Castro compare resemblance in the food neophobia categories of twins and non-twins siblings, finding evidence for heritable effects, albeit less than estimates from previous research. Brizot documents challenges to multiple pregnancies, reviews the efficacy of different interventions and notes that the best method for preventing preterm twin birth in mothers with a short cervix has not been determined. de Lima reports findings from a cross-sectional twin study of developmental enamel effects in which genetic influence on molar incisor hypomineralization was observed. Mendes and colleagues outline a study that will recruit young twins to assess variables related to oral health, determine if improvements in dental care affect quality