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Title: Nature, Nurture, and First Intercourse: Fitting Behavior Genetic Models to NLSY Kinship Data
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Rodgers, Joseph Lee Rowe, David C. Buster, Maury Allen |
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Nature, Nurture, and First Intercourse: Fitting Behavior Genetic Models to NLSY Kinship Data Presented: New Orleans, LA, Meetings of the Population Association of America, May 1996 Cohort(s): NLSY79 Publisher: Population Association of America Keyword(s): Adolescent Behavior; Adolescent Fertility; Adoption; Age at First Intercourse; Contraception; Gender Differences; Genetics; Kinship; Modeling; Pairs (also see Siblings); Peers/Peer influence/Peer relations; Sexual Behavior; Siblings; Simultaneity Permission to reprint the abstract has not been received from the publisher. Newcomer (1994) stated that "Partners, peers, parents (maybe even genes) and the community all influence [adolescent sexual] behavior" (p. 85). Udry and Campbell (1994) surveyed the literature and found only one small study that accounted for genetic influences on adolescent sexual behavior. Apparently, little research has been done to address the role that genetic influences play in various aspects of fertility behavior, or the tradeoff between genetic and environmental influences. Udry's work (e.g., Udry, 1988) suggests an important role of hormonal influences in both male and female sexual behavior, and biosocial models of adolescent sexuality are becoming increasingly popular (e.g., Hofferth, 1987; Rodgers & Rowe, 1993; Udry, 1988). Fisher's (1930) work raised doubts as to whether it would ever be fruitful to search for genetic influences on fertility behavior. Plomin, DeFries, and McClearn (1990), drawing on work by Fisher and Falconer (1981), explained that potential changes in relative fitness across generations due to a particular trait can be measured by the amount of additive genetic variance in that trait present in the population. They concluded that we should "expect heritability to be low for major components of fitness, such as fertility" (p. 285), and suggest that most genetic variance in such traits should be nonadditive. However, this expectation depends on a long enough period of time that traits with selective advantage can realize that advantage. Our investigation will treat age at first sexual intercourse in the U.S. population. During the past several centuries, there have been secular changes--both up and down--in the age at first intercourse. Furthermore, the development of reliable and widespread use of effective contraception must weaken the selective advantage offered by early onset of sexual behavior in societies with little or no contraceptive use. Such changes could certainly act to weaken the selective value of early onset of sexual activity. Given these changes, it is an important theoretical question to ask whether genes play a role in influencing onset of sexual behavior. At the same time, the role of environmental influences is also of particular interest and importance. Our modeling will simultaneously address the role of both types of influence. The data we will use to address the role of genetic and environmental influences on age at first intercourse come from the National Longitudinal Survey of Youth (the NLSY), a national probability sample of households that started with approximately 12,000 youth aged 14-21 in 1979. To separate the contribution of genetic versus environmental influences requires data from different kinship levels (e.g., monozygotic versus dizygotic twins; adoptive siblings versus full siblings; etc.). Little of this type of information is contained explicitly in the NLSY, although the household structure of the NLSY data results in many kinship links being contained in the data. We have recently developed a linking algorithm (Rodgers, 1996) that uses several variables in the NLSY files to classify kinship pairs into adoptive, half, and full sibling, twin, and cousin pairs. We will use this kinship structure along with a recently developed regression procedure, DF Analysis, (DeFries and Fulker, 1985; Rodgers, Rowe & Li, 1993) to analyze variance in age at first intercourse into that attributable to genetic, shared environmental, and nonshared environmental influences. Because patterns of sexual debut differ substantially across race and across genders, we will fit our models separately by these demographic categories. |
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Bibliography Citation
Rodgers, Joseph Lee, David C. Rowe and Maury Allen Buster. "Nature, Nurture, and First Intercourse: Fitting Behavior Genetic Models to NLSY Kinship Data." Presented: New Orleans, LA, Meetings of the Population Association of America, May 1996. |