Abstract
In most species with parental care, offspring disperse from the natal territory either at sexual maturity or when they are competent to survive independently. In humans and numerous avian species, dispersal from the natal family may not coincide with these developmental markers. This presents an adaptive puzzle, since delaying dispersal typically delays reproduction. Various ecological explanations for delayed dispersal in birds have been proposed and tested. Emlen (1995) suggested parallels between humans and birds with regard to the circumstances that influence family formation and dispersal timing. Work by other authors has applied Emlen’s model to humans using proxy measures of “Natal Territory Quality” (NTQ). Using the Panel Study of Income Dynamics, a longitudinal survey of U.S. families, I extract direct measures of NTQ to more rigorously test Emlen’s prediction that higher NTQ leads to later dispersal. I use two age-based cohorts (born in 1957 and 1967). Focusing on three dispersal events (residential dispersal, first marriage, and first reproduction), I test whether economic variables describing family of origin (NTQ) and local conditions influence dispersal age. Multiple linear regression analysis is employed to elucidate the relationships between dispersal and NTQ.
The independent variables appear to have different influences on the three dispersal events, suggesting differential salience of the independent variables for each dispersal type. Results also point to discrepancies across the two cohorts. For the older cohort, family income, father’s employment status, and local unemployment rate appear to influence the timing of residential dispersal. Age at first reproduction and age at first marriage are both influenced by parents’ education and household density; marriage timing is also affected by father’s employment status also affecting marriage timing. For the younger cohort, father’s employment status and household density affect residential dispersal timing, father’s employment status, mother’s education, and family income affect reproductive timing, and father’s occupational prestige affects marriage timing. Females experience all dispersal events earlier than males. All results above reflect significant regression coefficients. However, according to criteria of acceptance for the models tested, the hypothesis was supported only for reproductive dispersal timing in the 1957 cohort.
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