SOCIAL AND PSYCHOBIOLOGICAL REGULATION OF THE HUMAN CHILD’s HYPOTHALAMUS-PITUITARY-AXIS: AN ONTOGENETIC PERSPECTIVE A Dissertation presented to The Faculty of the Graduate School University of Missouri-Columbia In Partial Fulfillment Of the Requirement for the Degree Doctor of Philosophy by Davide Ponzi Dr. Frederick S. vom Saal, Dissertation Supervisor December 2011 The undersigned, appointed by the dean of the Graduate School, have examined the dissertation entitled SOCIAL AND PSYCHOBIOLOGICAL REGULATION OF THE HUMAN CHILD’S HYPOTHALAMUS-PITUITARY-AXIS: AN ONTOGENETIC PERSPECTIVE presented by Davide Ponzi, a candidate for the degree of Doctor of Philosophy and hereby certify that, in their opinion, it is worthy of acceptance. Professor Frederick vom Saal Professor Mark Flinn Professor Joel Maruniak Professor David Geary Professor Rex Cocroft 2 Volevo dirti qualcosa adesso che e’ notte e le parole se ne vanno… dirti che ti voglio bene, figlio, che il mio sogno sei tu. Osvaldo Soriano, L’ora senz’ombra Questo lavoro e’ dedicato alla memoria di mio padre e a mia madre, le cui vite fatte di sacrifici e sudore hanno reso, ai miei occhi, le loro piccole e quotidiane vittorie uno straordinario viaggio che non e’ ancora finito. 3 Acknowledgements This professional and life accomplishment would not have happened without the cultural and emotional support of many people. Everything began with two amazing professors that have been my sources of inspiration for the study of biology and evolution, Prof. Paola Palanza and Prof. Stefano Parmigiani. They are the ones that made me to love biology and that opened the possibility for me to come to Mizzou to meet Prof. Vom Saal and Prof. Maruniak, the two best advisors that a student would dream to have. Their infinitive knowledge and emotional support helped me to get through the ups and downs of the graduate school experience. Their support for my professional success was even more evident when they agreed that I could seek for an interdisciplinary research plan. And here, other two amazing professors came along, Prof. Flinn and Prof. Geary. Prof. Flinn, my dissertation supervisor, brought me to Dominica and allowed me to turn an idea into what I am proudly presenting in this dissertation. He also openly shared is knowledge and experience with me, which was a source of great inspiration and curiosity for the study of evolutionary anthropology. Mark, thank you for having introduced to me the great works and thoughts of Richard Alexander, I will be thankful to you for the rest of my life. Dave, you are the professor I would like to be one day: an energetic and successful scientist and a great advisor. I thank Prof. Cocroft for being part of my committee and for the great suggestions he gave me throughout out the all process. Special thanks go to my family, my sister Patrizia, my mom Zaira and my beloved father Pierino, that I miss every day more. What I would do to ii have the chance to hug you in these days Dad! Without them I would not have been the honest and idealist man I believe I am. To my wife, Jessica, thank you for being with me and make my life shining every day. Thanks to my Dominican friends Eugenia, Dwayne and the Abbots, they made my experience in Dominica delightful and unforgettable. And thank you to all my friends and people that shared with me parts of their lives. iii Table of Contents ACKNOWLEDGEMENTS ............................................................................... II TABLE OF CONTENTS ................................................................................. IV LIST OF TABLES...………………………………………………………………..VII LIST OF FIGURES ......................................................................................... IX ABSTRACT .................................................................................................... XI CHAPTER 1 .................................................................................................... 1 General Introduction ................................................................................................................ 1 1.1 Introduction ...................................................................................................................... 1 1.2 The organization of the dissertation ................................................................................. 2 1.3 Theoretical background: Evolution of the human child .................................................... 4 1.4 The social neuro-endocrinology of the human child: an ontogenetic perspective ........... 6 CHAPTER 2 .................................................................................................... 8 Day-to-day and year-to-year stability of cortisol and DHEA ................................................ 8 2.1 Introduction ...................................................................................................................... 8 2.2 Methods ......................................................................................................................... 13 2.2.1 Subjects and saliva collection ................................................................................. 13 2.2.2 Statistical analysis ................................................................................................... 14 2.3 Results ........................................................................................................................... 17 2.3.1 CORT daily and yearly change and day-to-day (year-to-year) measurement stability ...................................................................................................... 17 2.3.2 Differences between averaged mean values of cortisol across ages ..................... 17 2.3.3 DHEA daily and yearly change and day-to-day (year-to-year) measurement stability ............................................................................................................................. 17 2.3.4 Differences between averaged mean values of DHEA across ages ...................... 18 2.4 Discussion ...................................................................................................................... 19 CHAPTER 3 .................................................................................................. 30 Mother-child bond, stress response and social competence in a rural Dominican community........................................................................................................... 30 3.1 Introduction .................................................................................................................... 30 3.2 Methods ......................................................................................................................... 33 3.2.1 The village ............................................................................................................... 33 3.2.2 Participants and general description of the study ................................................... 33 3.2.3 Internal and externalizing behavior ......................................................................... 34 3.2.4 Social network ......................................................................................................... 35 iv 3.2.5 Mother-child bond ................................................................................................... 35 3.2.6 Behavioral assessment ........................................................................................... 36 3.2.7 Saliva sampling, handling and preparation ............................................................. 37 3.2.7.1 Saliva collection during regular days (no-interview) ............................................ 37 3.2.7.2 Saliva collection during the interview ................................................................... 38 3.2.8 Cortisol and DHEA .................................................................................................. 38 3.3 Statistical Analysis ......................................................................................................... 39 3.4 Results ........................................................................................................................... 41 3.4.1 Effect of the interview, comparing basal vs interview samples ............................... 41 3.4.2 Correlation analysis ................................................................................................. 41 3.4.3 Relationship between basal levels of cortisol and DHEA with mother-child bonds, externalizing behaviors and popularity. ................................................................ 42 3.5. Discussion ..................................................................................................................... 42 CHAPTER 4 .................................................................................................. 52 Sex biased maternal investment and sex differences in child’ sensitivity to stress ....................................................................................................................................... 52 4.1 Introduction .................................................................................................................... 52 4.2 Adaptive explanation of sex biased ratio in primate and humans ................................. 56 4.3 Adaptive models of sex biased investment after birth ................................................... 59 4.4 Mother-offspring relationships in free ranging and captive social