How do Early Experiences Affect the Timing of Sexual Development?
There can be little doubt that human beings have evolved to be able to function competently in a variety of different environments. But what enables this flexibility and adaptation? From the perspective of evolutionary developmental psychology, natural selection builds alternative developmental pathways or "strategies" into the design of the nervous system. Which strategy develops depends both on the genes we inherit from our parents and our childhood experiences, especially in the family.
My research, first in the United States and now in New Zealand, suggests that girls' experiences with their father and other adult males early in life may play an important role in entraining the development of alternative reproductive strategies. To investigate this hypothesis, my collaborators and I are studying whether girls who grow up in the same home with their biological father and who are physically and emotionally close to their dad tend to go through puberty later, delay sex and pregnancy, and show more reticence in forming sexual relationships (compared with girls who are fatherless or have more remote relationships with their dads).
Our research on this topic began by studying father-daughter relationships in early childhood (Ellis et al., 1999, 2003). We recruited a community sample of 5-year-old American girls and their families and made multiple visits to their homes, often observing parents and children around dinner time. We coded both positive aspects (e.g., encouragement, affectionate contact) and negative aspects (e.g., coercive discipline, harsh words) of father-daughter relationships. We also collected information about the amount of time that fathers spent in childcare, age of daughters at onset of father absence, and the quality of relationships between fathers and mothers. Daughters were then tracked annually throughout childhood and adolescence, at which time we asked about onset of puberty - if they had any pubic hair, if their breasts had begun to show, if they had gotten their first period. We found that girls from father-present homes tended to experience later puberty than did girls from father-absent homes, but that even within father-present homes more active caregiving by fathers and direct interaction with daughters at age 5 was associated with later puberty (Ellis et al., 1999). Most interesting, in a separate longitudinal study of girls growing up in father-absent homes, we found that more prolonged exposure by daughters to unrelated adult males (particularly stepfathers and mothers' boyfriends) forecast earlier puberty (Ellis & Garber, 2000).
These American samples, along with a New Zealand sample, have now been followed to adulthood. We have found dramatic effects of early father absence (particularly in the first five years of life) on risk for both early sexual activity and teenage pregnancy. For example, rates of teenage pregnancy increased from about 1/20 among father-present girls to 1/3 among early father-absent girls in the US sample and from about 1/30 among father-present girls to 1/4 among early father-absent girls in the NZ sample. These elevated rates were either not explained (in the US study) or only partly explained (in the NZ study) by family and personal disadvantages associated with father absence (Ellis et al., 2003). Again, consistent with our earlier research, exposure to stepfathers partly accounted for the relation between early father absence and risky sexual behavior.
Based on this research, I have developed a theory of the role of paternal investment in regulation of girls' sexual development (Ellis, 2004). This theory posits that girls detect and internally encode information specifically about the quality of paternal investment during approximately the first five years of life as a basis for calibrating the development of (a) neurophysiologic systems involved in timing of pubertal maturation and (b) related motivational systems, which make certain types of sexual behavior more or less likely in adolescence. My current research is primarily focused on testing various aspects of this theory.
What are the Neural and Hormonal Mechanisms that Underlie Variation in Sexual Development?
Biological reactivity to psychological stressors comprises a complex, integrated, and highly conserved repertoire of central neural and peripheral neuroendocrine responses designed to prepare the organism for challenge or threat. These responses, however, may also be among the physiological pathways by which psychological trauma influences timing of pubertal development.
Developmental experience plays a role, along with heritable, polygenic variation, in calibrating the response dynamics of stress reactivity systems, with early adversity biasing their combined effects toward a profile of heightened or prolonged reactivity. Conventional views of such high reactivity suggest that it is an atavistic and pathogenic legacy of an evolutionary past in which threats to survival were more prevalent and severe. Recent evidence, however, indicates that: (a) stress reactivity is not a unitary process, but rather incorporates counter-regulatory circuits serving to modify or temper physiological arousal, and (b) the effects of high reactivity phenotypes on psychiatric and biomedical outcomes are bivalent, rather than univalent, in character, exerting both risk-augmenting and risk-protective effects in a context-dependent manner (Boyce & Ellis, in press). These observations suggest that heightened stress reactivity may reflect, not simply exaggerated arousal under challenge, but rather an increased biological sensitivity to context, with potential for negative health effects under conditions of adversity and positive effects under conditions of support and protection.
From an evolutionary perspective, the developmental plasticity of the stress response systems, along with their structured, context-dependent effects, suggests that these systems may constitute conditional adaptations: evolved psychobiological mechanisms that monitor specific features of childhood environments as a basis for calibrating the development of stress response systems to adaptively match those environments (Boyce & Ellis, in press). Taken together, these theoretical perspectives generate a novel, testable hypothesis: that there is a curvilinear, U-shaped relation between early exposures to adversity and the development of stress-reactive profiles, with high reactivity phenotypes disproportionately emerging within both highly stressful and highly protected early social environments. This hypothesis has received provisional support in two studies of early development and psychopathology (Ellis, Essex, & Boyce, in press).
My current work investigates the complementary hypothesis that there is also curvilinear, U-shaped relation between early adversity-support and timing of puberty, with later pubertal development occurring in both acutely stressful and exceptionally supportive early family environments (Ellis, 2004). Initial analyses suggest that heightened autonomic reactivity in preschool is associated with later onset of puberty. Our goal is to examine whether the hypothesized curvilinear relation between family adversity-support and pubertal timing is mediated by heightened reactivity in one or more of the stress response systems.
How do we Regulate Investment in Dating and Marital Relationships?
My research in this domain focuses on developing and empirically testing a causal model of the personality and cognitive processes that underlie day-to-day variations in investment in romantic relationships. This research has followed two tracks. First, I have focused on developing and validating new multi-dimensional measures of relationship investment (Ellis, 1998) and relationship dependence (Ellis, Simpson, & Campbell, 2002). The scale development phase of this research was necessitated by the need for new measures to enable testing of the theory and reflects my long-standing interest in psychometrics. Second, I have sought to test the causal model, first developed in my dissertation (Ellis, 1995), specifying three features of individuals and dyads that should influence patterns of investment behavior: enduring individual differences in orientation toward relationships (e.g., attachment styles, sociosexual orientation), subjective beliefs of each partner about the difficulty in replacing the other with a comparable alternative (i.e., relative dependence), and variations in the levels and types of investment that are received from one's partner. Specific facets of the model have received empirical support (Ellis, 1998; Ellis & Malamuth, 2000; Ellis, Simpson, & Campbell, 2002), and I am now in the process of testing the full model in a longitudinal study of dating couples.
One of the most interesting findings to emerge from this research has been the relative independence of love and anger in predicting patterns of investment in dating relationships. In longitudinal work on antecedent of dating violence, I have found that although aggressive beliefs and behavior in childhood predict levels of aggression toward dating partners, they do not predict levels of love, trust, and commitment to dating partners. This suggests that the psychological processes that underlie antisocial behavior in dating relationships may be independent of the psychological processes that underlie prosocial behavior. Along these lines, I have found that variations in intensity of love that individuals experience toward their partners are independent of variations in intensity of anger that individuals experience during conflict-evoking episodes with their partners. This independence (rather than counteraction) of love and anger may help explain the cycle of violence in many dating and marital relationships (Ellis & Malamuth, 2000).
An important focus of my current work on close relationships is examining the role of self-esteem in mate selection and regulation of investment (Ellis & Kelley, 1999; Kirkpatrick & Ellis, 2001, in press). Specifically, I am testing the hypothesis that self-esteem functions to guide individuals to select and maintain high-quality, yet defensible social relationships.
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