Temporal trends in migration in the Aland Islands: effects of population size and geographic distance.

Using a model developed by Relethford (1992), we assess temporal trends (1750-1949) in marital migration in the Aland Islands, Finland, in relation to both geographic distance and population size. The 200-year time period was divided into four 50-year periods. For all time periods both geographic distance and population size are important determinants of migration among 15 Lutheran parishes. The geographic distance parameter of the model decreases significantly over time, and the population size parameter fluctuates slightly but shows no significant change over time. For all time periods migration is negative density dependent, indicating that there is greater relative flow from larger to smaller subdivisions. Even though both the geographic distance and population size parameters are statistically significant, the analysis suggests that geographic distance has a greater relative effect on migration than population size. There is a clear indication of isolate breakdown during the last two time periods (1850-1899 and 1900-1949). Residual analysis indicated that the smallest parish (Sottunga) was a major outlier that showed greater exogamy (less endemicity) than expected from the model.

Marital exogamy in the Aland Islands, Finland, 1750-1949.

Marriage records from 1750 through 1949 were used to examine effects of population size, geographic distance, and temporal change on rates of marital exogamy in the Aland Islands, Finland. Exogamy rates for individuals (not couples) were computed for 15 Aland parishes in each of four 50-year time periods, giving a total of 60 observations. These rates were analysed with respect to population size using a quadratic regression model. Regression analyses were also used to examine the relationship of marital exogamy with two measures of geographic distance--average distance to all other parishes and nearest-neighbour distance. Analysis of variance was used to examine temporal trends. Multiple regression analyses were used to examine all of these factors simultaneously. Marital exogamy is highest in smaller and larger populations, and less in medium-sized populations. Higher exogamy rates in small populations are related to the lack of available mates in small groups. Higher exogamy rates in larger populations may reflect economic attraction of larger groups. Exogamy rates are lower in the more geographically isolated parishes. From 1750 through 1899 there is little change in exogamy rates, whereas exogamy rates double after 1900. This temporal change reflects changes in transportation technology and other cultural factors promoting increased migration. The multiple regression model shows population size, geographic distance, and temporal change are all significant correlates of exogamy, collectively explaining a large percentage of variation in rates (R2 = 0.79).

Age and sex differentials in mortality during two nineteenth century population crises.

"The exceptionally detailed Finnish materials are used to examine age- and sex-specific mortality in different regions during the country's last famine, the Great Famine of the 1860s. This is compared with another mortality crisis, the 1808-09 War. The results show that in cases when multiple infectious diseases were responsible for elevated mortality, the increases for different age categories were, by and large, proportional to the levels prevailing during normal times. However, excess mortality showed more variability for children. Furthermore, age- and sex-specific social behaviour (specifically large-scale temporary migration) during the crisis period shaped the age patterns and sex differentials in mortality." (SUMMARY IN FRE)

War demography: the impact of the 1808-09 war on the civilian population of Aland, Finland.

"A pre-industrial population crisis caused by a war is examined using Finnish historical records. During the War of Finland (1808-09) the Swedish military deployed on the Aland Islands helped spread infectious diseases among the civilian population. The result was a short but intense period of high mortality. This article focuses on the short-term demographic impact of this crisis. Changes in age-specific and sex-specific mortality, fertility, and nuptiality are explored....A projection, assuming that the crisis did not occur, indicates that Aland's population losses were never compensated." (SUMMARY IN FRE)

Predicting smallpox epidemics: A statistical analysis of two Finnish populations.

We analysis data on death due to smallpox in two subdivided Finish populations, the relatively isolated Åland Islands and the mainland parish of Kitee. The data span a 135-year time period (1750-1885). Logisitic regression and Cox proportional hazards models are used to assess the effects of predictive variables on (1) the probability that an individual subdivision experiences an epidemic and (2) the length of the time period between two epidemics in each subdivision. The predictive variables include population sizes, migration rates, geographic distance, and presence or absence of vaccination. Vaccination was found to be the single most important predicative variable (odds ratio = 6.3 in Åland and 4.4 in Kitee). No other variable were significant predicators in Kitee, while geographic distance was an additional significant predicator in Åland (odds ratio = 1.05). As expected, vaccination and geographic distance were both negatively associated with the probability of epidemic occurrence. The Mantel regression approach was used to evaluate the effects of independent variables on the probability that any two subdivisions experienced the same epidemic. Between-subdivision migration rates were the most important predictive variable here, and population size was an important predictor in Åland but not in Kitee. The differing results in these two populations are explained in terms of differences in ecological setting and social organization.

Marital migration and genetic structure in Kitee, Finland.

A genetic analysis of marital migration in Kitee, Finland, is presented. The data are based on 9970 marriages which took place between 1750 and 1877. The results of this analysis are compared with those of previous studies of the population of the Aland Islands, Finland. Analysis of inter-subdivision genetic kinship matrices shows that genetic heterogeneity in Kitee is substantially less than in Aland. This is due primarily to higher rates of migration, both between subdivisions and from outside the population, in Kitee compared to Aland. These differences in migration rates can in turn be attributed to greater geographic isolation in Aland and the contrasting social structures of the two populations. Because of differences in geographic structure and population distribution, geographic distance between subdivisions is a better predictor of inter-subdivision genetic kinship in Kitee than in Aland. The Aland Islands are known to have high frequencies of several otherwise rare genetic diseases; in addition, these diseases are distributed very non-randomly among Aland's subdivisions. The genetic structure results presented here suggest that Kitee should have a less unique distribution of genetic diseases.

Twinning rate in Scandinavia, Germany and The Netherlands during years of privation.

Twinning rates were studied in Swedes, Aland Islanders, Finns, Germans, and Dutch during years of starvation when death rates were two to three times higher than average. In contrast to the situation among some animals, this study suggests that nutrition above a certain threshold is unimportant for human reproduction, including twinning. The twinning rates for these different populations display marked temporal differences, but low values in the twinning rate are not consistently associated with periods of epidemics, famine, or similar nutritional stress. After years of privation and/or separation of spouses, a rapid "catch-up effect" can often be seen in the twinning rates, as well as marriage and birth rates. Psychoendocrine factors and interparental immunological conditions that may be involved in this phenomenon are discussed.

Population structure in the Connecticut Valley. I. Marital migration.

This study reports on an analysis of marital migration among 12 communities in the Connecticut River Valley of Massachusetts during the years 1790-1849. Genetic inferences are drawn, and the requisite assumptions considered. The effect of geographic distance on genetic kinship is predicted using Malécot's isolation-by-distance model. The resulting estimates are discussed in terms of geographic and historical factors. The configuration of communities as predicted by kinship values approximates closely their actual geographic locations. Estimated genetic heterogeneity was low for the historical Connecticut Valley population, and community isolation breaks down rapidly over time. The region thus assumes its place among a number of sedentary, agricultural populations for which the isolation-by-distance model provides an adequate representation. A regression analysis which includes variables in addition to distance indicates that historical and economic factors contribute some additional explanatory power to the distribution of mating frequencies.

Historical epidemiology of smallpox in Aland, Finland: 1751-1890.

We analyze a 140-year series of smallpox deaths in the Aland Islands, Finland. Vaccination, introduced in 1805, dramatically reduced the annual number of smallpox deaths. It also influenced the age distribution of smallpox deaths, changing smallpox from a childhood disease before 1805 to one which affected both adults and children after 1805. This appears to be due to the fact that Alanders were usually vaccinated only once during childhood and often lost their immunity during adulthood. Spectral analysis of the prevaccination time series of smallpox deaths demonstrates a strong seven-year periodicity, reflecting the amount of time necessary to build up a cohort of nonimmune individuals. After the introduction of vaccination, the periodicity changes to eight years. The probability that a parish in Aland was affected by a smallpox epidemic is shown to be highly correlated with migration patterns and parish population sizes.

Population structure of Alaskan and Siberian indigenous communities.

Genetic data consisting of 14 red cell antigen groups and 11 serum and erythrocytic protein marker systems from four Eskimo populations of the Norton Sound area of Alaska are reported. The population structure of these four groups in analyzed both separately and within the larger context by comparison to 15 other circumpolar groups. These analyses reveal a good fit between genetic structure, geographic distribution, linguistic affiliation, and the ethnohistory of the region.

The genetic structure of finland.

The Finnish gene pool derives primarily from a relatively homogeneous Finno-Ugric population established during the Iron Age (100 B.C.-800 A.D.) in the southwest and southeast of Finland. Gene flow from Sweden to the southwest coastal areas, dating from prehistoric times, as well as the patterns of settlement and migration throughout Finland during the past 1000 years, appear to have been the major biosocial factors underlying the genetic structure of the contemporary population. Analysis of genetic variation and covariation at nine polymorphic loci in a large random sample of rural Finns, partitioned into either 8 countries or 27 geographic districts, showed that all of the essential features of the genetic structure suggested by the archaeological and historical data could be distinguished. Procedures for obtaining inference on the genetic structure of such a population are reviewed, including coefficients of similarity and (genetic) distance among subpopulations, the relation between linear or planar geographic structure and genetic covariation, and the methods for describing allelic differentiation. Bias resulting from the inappropriate assumption of a simple phylogenetic model can be substantial, expecially for the analysis of isolation by distance; procedures for avoiding misleading inference on the genetic structure are demonstrated.