The measurement of ancestral roots with genealogical data

ABSTRACT

This study presents a new method to measure the depth of ancestral roots in a population. This method sheds light on the migratory movements that led to present-day population distribution across space. The method was applied to a dataset of 5,100 ascending genealogies from 17 regions of the province of Quebec (Canada). Dates of marriage of the earliest ancestors married in the same region as their descendants were used to measure the age of individual ancestral roots. The average regional ages vary between 16 and 157 years, while some individual roots reach as far back as 300 years in the same region. The proposed method can be useful for assessing how deeply rooted a contemporary population is at a local, regional, or other geographical level.

KEYWORDS:

• Ancestral roots
• genealogies
• population database
• regional founders

Acknowledgements

The author wishes to thank Ève-Marie Lavoie and Jean-Sébastien Bournival (BALSAC Project, Université du Québec at Chicoutimi) for their technical assistance. Many thanks also go to the two anonymous reviewers for their helpful comments and suggestions.

Funding

This research was supported by the Social Sciences and Humanities Research Council of Canada (grant number 435-2015-0638).

Notes

1. These marriages are essentially Catholic. Marriages of other faiths or unions which have not been the subject of a marriage certificate were thus excluded from the samples. A total of 919,507 marriages were recorded in Quebec between 1966 and 1985 (Girard, Charbonneau, and Payeur 2016), of which approximately 87% were Catholic (the exact proportion is not known). For each region, the distribution of subjects according to their place of marriage is proportional to the population of the municipalities of the region according to the 1976 census (mid-point of the subjects' marriage period).

2. In some cases, due to missing data, information about the first immigrant was unknown. Overall, 97% of the total genetic contribution to the 5,100 subjects was traced to known immigrants.

3. Regional founders must not be confused with immigrant founders. Immigrant founders refer to the territory of Quebec as a whole, whereas regional founders refer to specific regions of Quebec. Hence, the genealogical branches do not necessarily end with regional founders (in fact, most branches do not). Since all regional founders are known, their genetic contribution to the subjects is totally (100%) explained (there is no missing data).

4. Some founders can appear several times in a single genealogy, through different branches of various lengths. The probability of multiple appearances increases with the number of generations separating the founder and the subject. For example, in the Capitale-Nationale genealogies, one couple of regional founders who were married in 1657 (from eight to 13 generations back) appears 1,668 times in the 300 genealogies, for an average of 5.6 appearances per genealogy; this couple explains 0.97% of the region's gene pool. Most founders, however, appear only a few times. In the Capitale-Nationale genealogies, 53% of the regional founders appear less than four times in the 300 genealogies; the average among all regional founders is 25 appearances in the 300 genealogies, for an average of 0.08 appearance per genealogy and an average genetic contribution of 0.03%.

5. As stated previously, all regional founders have been identified in the genealogies. In the case of missing data, the age of regional ancestral roots could still be calculated based on all known regional founders, assuming that the average contribution of unknown founders is similar to that of known founders. Alternatively, the contribution of the earliest ancestors (going up every genealogical branch) married in the same region as the subject could be used if the place of marriage of their parents is unknown; in such cases, the age of regional ancestral roots must be considered as a minimal value.

6. Since these results were obtained using data from ascending genealogies, they do not represent all the migration movements that occurred in the regions since the beginning of settlement. The objective of this study was to measure the ancestral roots of contemporary people in the population based on information about their ancestors. As such, results cannot reflect migrations of people who did not have descendants in the contemporary population. In fact, they may be best interpreted as a kind of “resulting intergenerational interregional migration” in Quebec since the early seventeenth century.