Academic journal article Population

Familial and Environmental Influences on Longevity in Historical Quebec

Academic journal article Population

Familial and Environmental Influences on Longevity in Historical Quebec

Article excerpt

The dramatic increase in life expectancy witnessed over the last two centuries in developed nations has no precedent in human history. The improvement has been general and observed across most strata of society. As populations continue to age, there is a need to understand mortality differentials, whether environmental or genetic in nature. Paradoxically, old age mortality in modern medicalized contexts may not be the ideal setting to address those differences. Genetic and other effects in modern populations can be masked by the prolongation of life through public health and medical technology (Desjardins, 2001; Olshansky et al., 2002).

An alternative to the study of current mortality patterns at older ages is to focus on genealogical records from pre-industrial populations. One of the most salient issues in the literature has been the examination of the familial transmission of longevity from one generation to the next. Such studies have addressed the proportion of variation in the lifespan originating from genetic factors and have produced heritability estimates that range from zero to a moderate value of 0.33 (Cournil et al., 2000; Kerber et al., 2001). The extent and significance of the association in each of the possible parent-offspring pairs (i.e. father-son, father-daughter, mother-son, and mother-daughter) reported in many studies are not clear, and show considerable variation from one to the next.

Some studies have found a stronger paternal-offspring association (Gavrilov and Gavrilova, 2001), while others have found a stronger maternal-offspring association (Mitchell et al, 2001). Among the European aristocracy, Gavrilova and Gavrilov (2001) noticed a positive linear association between mothers living past 85 years and their daughters' longevity. They also reported a paternal-daughter association when fathers lived past age 75. These threshold ages were considered as "demarcation points'" for longevity. Bocquet-Appel and Jakobi (1990) believed that the paternal-child resemblance exceeded that of the maternal-child similarities because of the high levels of maternal mortality in historical times. Otherwise, the influence of both parents was thought to be identical. To further complicate matters, sex-specific parental-offspring resemblance may vary over time, as shown in the nineteenth century British Peerage Data (Westendorp and Kirkwood, 2001), or by socioeconomic status, as revealed by a comparison of rural Finns with the European aristocracy from 1600 to 1889 (Korpelainen, 2000).

Other enquiries have focused on sibling pairs, which provide additional evidence on the components of longevity. It was found, for instance, that the siblings of New England centenarians had a 50% lower risk of death than that of the general population (Perls et al., 1998, 2002a; Perls and Terry, 2003). Among the Mormons in Utah (1870-1907), first-degree relatives of siblings (same father and same mother) surviving to the 95th percentile were approximately twice as likely to survive to the 95th percentile as controls (Kerber et al., 2001). A similar pattern was also observed in the Icelandic population (1870-1900) (Gudmundsson et al., 2000). Further, a strong resemblance among brothers and a significant but, weaker correlation for sister-sister pairs were also reported for the Pennsylvanian Amish born prior to 1890 (Mitchell et al., 2001). Overall, the phenotypic resemblance between siblings is expected to be higher than between parents and their children because of dominance interaction(1), age similarities and exposure to more similar social and environmental conditions over the life course (Perls et al., 2002b).

The above studies provide excellent insight into familial longevity, but they are not without limitations. First, most studies do not test for the possibility of other coincidental associations, such as with other family members. When analysing parent-offspring associations, most studies do not simultaneously control for the potential influence of sibling and spousal survival on longevity. …

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