Intergenerational Correlation of Effective Family Size in Early Que ´ bec (Canada) ALAIN GAGNON 1 * AND EVELYNE HEYER 2 1 Programme de recherche en de ´mographie historique (PRDH), De ´partement de de ´mographie, Universite ´ de Montre ´al, Succ. Centre-Ville, Montre ´al, Que ´bec, Canada 2 CNRS—Laboratoire d’anthropologie biologique, Muse ´e de l’Homme, Paris, France ABSTRACT The use of a comprehensive demographic database of the early French Canadian population (1608–1800) reveals an almost null impact of parents’ fertility on children’s fertility (r  0.01–0.05), which contradicts the commonly held view that family size has a tendency to run in families. However, in this population, there is a clear transmission from one generation to the next of the effective family size within a given geographical area (EFS, defined as the number of children that settle per settled individual). Three types of correlations between EFS of parents and children are presented in order to account for the impact of socio-demographic differentials. Individuals who belong to a large sibship and who settled in a given subdivision tend to encourage the settlement of a high number of their own children in the same subdivision (r  0.1–0.3). An additional correlation was introduced to see if geographically-based differentials of EFS can account for the differential of founders’ regional genetic contribution. The analysis shows that EFS correlation has a definite impact on the concentration of a population’s gene pool (it increases it by 20%–45%), and partly accounts for the differences between subdivisions in this regard. Am. J. Hum. Biol. 13:645–659, 2001. © 2001 Wiley-Liss, Inc. In many studies, positive correlations have been reported between the number of children born to a family and the number of children within the husband’s and/or wife’s family. In other words, it appears that fam- ily size has a tendency to run in families. This phenomenon was first interpreted as evidence of the inheritance of fecundity (i.e., biological capacity to reproduce), and at- tempts have been made to assess the contri- bution of inheritance to the total variation in individual reproduction. The earliest study goes back to the turn of the century when Pearson et al. (1899) used records of the British peerage to investigate fertility correlations. Working with several thou- sand pairs of mothers and daughters, they found a positive correlation between daugh- ters and mothers in fertility, which was in- terpreted as an inherited capacity to repro- duce. Some 30 years later, Fisher (1930) used these data to estimate the genetic vari- ance in fertility and concluded that about 40% of the observed variance in fertility was due to heredity. However, from a re-examination of Pear- son’s data, Williams and Williams (1974) have shown that secular change, i.e., emer- gence of birth control practices, contributed significantly to the correlation between sib- ship size and progeny number. They con- cluded that attempts to measure the heri- table component in fertility are neither valid nor reliable because of the overwhelm- ing contribution of the social environment to fertility in human populations. These con- clusions were reinforced by Langford and Wilson (1985), who, using 16 th - to 19 th -cen- tury family reconstitutions of seven British parishes, showed that there was no evi- dence for the transmission of fecundity. Concomitant with this failure to identify an underlying biological determinant of in- tergenerational fertility, there has been a shift toward concern with socioeconomic fac- tors that affect the transmission of fertility behavior (Ben-Porath, 1975; Johnson and Stokes, 1976; Thornton, 1980; Thornton et al., 1986). Among cohorts of marriages where the prevalence of birth control could be assumed, a certain traditional continuity in family-building habits was also offered as an explanation of fertility differentials (Anderton et al., 1987). In summary, it appears that when paren- tal family size exerts a definite, even small, differentiating effect on fertility (i.e., the de- *Correspondence to: Alain Gagnon, Laboratoire d’anthro- pologie biologique, Muse ´e de l’Homme, 17 Place du Trocade ´ro, 75016 Paris, France. E-mail: gagnoal@mnhn.fr Received 31 July 2000; Revision received 30 January 2001; Accepted 31 January 2001 AMERICAN JOURNAL OF HUMAN BIOLOGY 13:645–659 (2001) © 2001 Wiley-Liss, Inc. PROD #M20057R2