NATURE, NURTURE AND FIRST SEXUAL INTERCOURSE IN THE USA: FITTING BEHAVIOURAL GENETIC MODELS TO NLSY KINSHIP DATA

Findings are reported from a behavioral genetic analysis of age at first intercourse accounting for genetic shared environmental and selected non-shared environmental influences. The findings are based upon data from the nationally representative National Longitudinal Survey of Youth (NLSY) began in 1979 as a household probability sample of all people aged 14-21 years in selected households with 11406 civilian respondents. The original sample has been followed on a yearly basis since 1979 with more than 90% continuation through 1992. Many kinship links exist in the NLSY files including twins. A newly developed kinship linking procedure was used which identifies links for cousins half siblings full siblings and twins in the NLSY. Analysis of the data suggest a genetic influence in the overall dataset and also among Whites and in male-male and opposite sex pairs. However genetic influences were very small or non-existent for Blacks and female-female pairs. Shared environmental influences were small for most subsets of the data but moderate for female-female pairs. Study findings support the existence of genetic influences and implicate non-shared environmental influences as being important determinants of the timing of loss of virginity among US adolescents and young adults.