The demographic history of the northern european countries in the eighteenth century

Grandmother presence improved grandchild survival against childhood infections but not vaccination coverage in historical Finns

Grandmother presence can improve the number and survival of their grandchildren, but what grandmothers protect against and how they achieve it remains poorly known. Before modern medical care, infections were leading causes of childhood mortality, alleviated from the nineteenth century onwards by vaccinations, among other things. Here, we combine two individual-based datasets on the genealogy, cause-specific mortality and vaccination status of eighteenth- and nineteenth-century Finns to investigate two questions. First, we tested whether there were cause-specific benefits of grandmother presence on grandchild survival from highly lethal infections (smallpox, measles, pulmonary and diarrhoeal infections) and/or accidents. We show that grandmothers decreased all-cause mortality, an effect which was mediated through smallpox, pulmonary and diarrhoeal infections, but not via measles or accidents. Second, since grandmothers have been suggested to increase vaccination coverage, we tested whether the grandmother effect on smallpox survival was mediated through increased or earlier vaccination, but we found no evidence for such effects. Our findings that the beneficial effects of grandmothers are in part driven by increased survival from some (but not all) childhood infections, and are not mediated via vaccination, have implications for public health, societal development and human life-history evolution.

Mortality in the Western Pyrenees during the 18th century. Data from the parish register of the village of Arudy (1741-1800), Bearn, France

OBJECTIVES

We aimed to determine the public health status of an 18th century mountain locality.

METHODS

We collected data registered in parish death certificates from Arudy, a small village in the French Pyrenees during the period 1741-1800.

RESULTS

Two thousand and six hundred and sixty-three cases were studied. About 50% of deaths occurred during the first 10 years of life. There were some particularities in deaths pattern with regards to age categories between males and females and seasonality. A fraction of individuals died at advanced ages (24.1% ≥60 years and of note three cases ≥100 years). The cause of death was reported in only 2.2% of cases (nearly always sudden fatalities). Maternal mortality could not be precisely determined. Throughout this period we identified a series of mortality crises which targeted mostly children and were probably in relation with undocumented epidemics.

CONCLUSIONS

These data offer some clues about the sanitary situation of an European mountain community during the 18th century.

Grandmotherhood across the demographic transition

Grandmothers provide key care to their grandchildren in both contemporary and historic human populations. The length of the grandmother-grandchild relationship provides a basis for such interactions, but its variation and determinants have rarely been studied in different contexts, despite changes in age-specific mortality and fertility rates likely having affected grandmotherhood patterns across the demographic transition. Understanding how often and long grandmothers have been available for their grandchildren in different conditions may help explain the large differences between grandmaternal effects found in different societies, and is vital for developing theories concerning the evolution of menopause, post-reproductive longevity, and family living. Using an extensive genealogical dataset from Finland spanning the demographic transition, we quantify the length of grandmotherhood and its determinants from 1790–1959. We found that shared time between grandmothers and grandchildren was consistently low before the demographic transition, only increasing greatly during the 20^th century. Whilst reduced childhood mortality and increasing adult longevity had a role in this change, grandmaternal age at birth remained consistent across the study period. Our findings further understanding of the temporal context of grandmother-grandchild relationships, and emphasise the need to consider the demography of grandmotherhood in a number of disciplines, including biology (e.g. evolution of the family), sociology (e.g. changing family structures), population health (e.g. changing age structures), and economics (e.g. workforce retention).

Limited support for the X-linked grandmother hypothesis in pre-industrial Finland

The level of kin help often depends on the degree of relatedness between a helper and the helped. In humans, grandmother help is known to increase the survival of grandchildren, though this benefit can differ between maternal grandmothers (MGMs) and paternal grandmothers (PGMs) and between grandsons and granddaughters. The X-linked grandmother hypothesis posits that differential X-chromosome relatedness between grandmothers and their grandchildren is a leading driver of differential grandchild survival between grandmother lineages and grandchild sexes. We tested this hypothesis using time-event models on a large, multigenerational dataset from pre-industrial Finland. We found that the presence of an MGM increases grandson survival more than PGM presence, and that granddaughter survival is higher than that of grandsons in the presence of a PGM. However, there was no support for the key prediction that the presence of PGMs improves granddaughter survival more than that of MGMs, diminishing the overall support for the hypothesis. Our results call for alternative explanations for differences in the effects of maternal and paternal kin to grandchild survival in humans.

Predicting global variation in infectious disease severity: A bottom-up approach

BACKGROUND AND OBJECTIVES

Understanding the underlying causes for the variation in case-fatality-ratios (CFR) is important for assessing the mechanism governing global disparity in the burden of infectious diseases. Variation in CFR is likely to be driven by factors such as population genetics, demography, transmission patterns and general health status. We present data here that support the hypothsis that changes in CFRs for specific diseases may be the result of serial passage through different hosts. For example passage through adults may lead to lower CFR, whereas passage through children may have the opposite effect. Accordingly changes in CFR may occur in parallel with demographic transitions.

METHODOLOGY

We explored the predictability of CFR using data obtained from the World Health Organization (WHO) disease databases for four human diseases: mumps, malaria, tuberculosis and leptospirosis and assessed these for association with a range of population characteristics, such as crude birth and death rates, median age of the population, mean body mass index, proportion living in urban areas and tuberculosis vaccine coverage. We then tested this predictive model on Danish historical demographic and population data.

RESULTS

Birth rates were the best predictor for mumps and malaria CFR. For tuberculosis CFR death rates were the best predictor and for leptospirosis population density was a significant predictor.

CONCLUSIONS AND IMPLICATIONS

CFR predictors differed among diseases according to their biology. We suggest that the overall result reflects an interaction between the forces driving demographic change and the virulence of human-to-human transmitted diseases.

Evolutionary ecology of human birth sex ratio under the compound influence of climate change, famine, economic crises and wars

1. Human sex ratio at birth at the population level has been suggested to vary according to exogenous stressors such as wars, ambient temperature, ecological disasters and economic crises, but their relative effects on birth sex ratio have not been investigated. It also remains unclear whether such associations represent environmental forcing or adaptive parental response, as parents may produce the sex that has better survival prospects and fitness in a given environmental challenge. 2. We examined the simultaneous role of wars, famine, ambient temperature, economic development and total mortality rate on the annual variation of offspring birth sex ratio and whether this variation, in turn, was related to sex-specific infant mortality rate in Finland during 1865-2003. 3. Our findings show an increased excess of male births during the World War II and during warm years. Instead, economic development, famine, short-lasting Finnish civil war and total mortality rate were not related to birth sex ratio. Moreover, we found no association between annual birth sex ratio and sex-biased infant mortality rate among the concurrent cohort. 4. Our results propose that some exogenous challenges like ambient temperature and war can skew human birth sex ratio and that these deviations likely represent environmental forcing rather than adaptive parental response to such challenges.

Male twins reduce fitness of female co-twins in humans

In mammals, including humans, female fetuses that are exposed to testosterone from adjacent male fetuses in utero can have masculinized anatomy and behavior. However, the reproductive consequences of such prebirth sex-ratio effects for offspring and their implications for maternal fitness remain unexplored. Here we investigate the effects of being gestated with a male co-twin for daughter lifetime reproductive success, and the fitness consequences for mothers of producing mixed-sex twins in preindustrial (1734-1888) Finns. We show that daughters born with a male co-twin have reduced lifetime reproductive success compared to those born with a female co-twin. This reduction arises because such daughters have decreased probabilities of marrying as well as reduced fecundity. Mothers who produce opposite-sex twins consequently have fewer grandchildren (and hence lower fitness) than mothers who produce same-sex twins. Our results are unlikely to be a consequence of females born with male co-twins receiving less nutrition because such females do not have reduced survival and increases in food availability fail to improve their reproductive success. Nor are our results explained by after-birth social factors (females growing up with similarly aged brothers) because females born with a male co-twin have reduced success even when their co-twin dies shortly after birth and are raised as singletons after birth. Our findings suggest that hormonal interactions between opposite-sex fetuses known to influence female morphology and behavior can also have negative effects on daughter fecundity and, hence, maternal fitness, and bear significant implications for adaptive sex allocation in mammals.

Fitness benefits of prolonged post-reproductive lifespan in women

Most animals reproduce until they die, but in humans, females can survive long after ceasing reproduction. In theory, a prolonged post-reproductive lifespan will evolve when females can gain greater fitness by increasing the success of their offspring than by continuing to breed themselves. Although reproductive success is known to decline in old age, it is unknown whether women gain fitness by prolonging lifespan post-reproduction. Using complete multi-generational demographic records, we show that women with a prolonged post-reproductive lifespan have more grandchildren, and hence greater fitness, in pre-modern populations of both Finns and Canadians. This fitness benefit arises because post-reproductive mothers enhance the lifetime reproductive success of their offspring by allowing them to breed earlier, more frequently and more successfully. Finally, the fitness benefits of prolonged lifespan diminish as the reproductive output of offspring declines. This suggests that in female humans, selection for deferred ageing should wane when one's own offspring become post-reproductive and, correspondingly, we show that rates of female mortality accelerate as their offspring terminate reproduction.

Reproductive investment in pre-industrial humans: the consequences of offspring number, gender and survival

The number and gender of offspring produced in a current reproductive event can affect a mother's future reproductive investment and success. I studied the subsequent reproductive outcome of pre-industrial (1752-1850) Finnish mothers producing twins versus singletons of differing gender. I predicted that giving birth to and raising twins instead of singletons, and males instead of females, would incur a greater reproductive effort and, hence, lead to larger future reproductive costs for mothers. I compared the mothers' likelihood of reproducing again in the future, their time to next reproduction and the gender and survival of their next offspring. I found that mothers who produced twins were more likely to stop breeding or breed unsuccessfully in the future as compared with women of a similar age and reproductive history who produced a same-gender singleton child. As predicted, the survival and gender of the offspring produced modified the costs of reproduction for the mothers. Giving birth to and raising males generally appeared to be the most expensive strategy, but this effect was only detected in mothers who produced twins and, thus, suffering from higher overall costs of reproduction.

Adaptive sex ratio variation in pre-industrial human (Homo sapiens) populations?

Sex allocation theory predicts that in a population with a biased operational sex ratio (OSR), parents will increase their fitness by adjusting the sex ratio of their progeny towards the rarer sex, until OSR has reached a level where the overproduction of either sex no longer increases a parent's probability of having grandchildren. Furthermore, in a monogamous mating system, a biased OSR is expected to lead to lowered mean fecundity among individuals of the more abundant sex. We studied the influence of OSR on the sex ratio of newborns and on the population birth rate using an extensive data set (n = 14,420 births) from pre-industrial (1775-1850) Finland. The overall effect of current OSR on sex ratio at birth was significant, and in the majority of the 21 parishes included in this study, more sons were produced when males were rarer than females. This suggests that humans adjusted the sex ratio of their offspring in response to the local OSR to maximize the reproductive success of their progeny. Birth rate and, presumably, also population growth rate increased when the sex ratio (males:females) among reproductive age classes approached equality. However, the strength of these patterns varied across the parishes, suggesting that factors other than OSR (e.g. socioeconomic or environmental factors may also have influenced the sex ratio at birth and the birth rate.

A theory of technophysio evolution, with some implications for forecasting population, health care costs, and pension costs

We argue that over the past 300 years human physiology has been undergoing profound environmentally induced changes made possible by numerous advances in technology. These changes, which we call technophysio evolution, increased body size by over 50%, and greatly improved the robustness and capacity of vital organ systems. Because technophysio evolution is still ongoing, it is relevant to forecasts of longevity and morbidity and, therefore, to forecasts of the size of the elderly population and pension and health care costs.

Differentials in demographic responses to annual price variations in pre-revolutionary France

"An examination of the annual responses of vital events to variations in wheat prices among groups of parishes in the city of Rouen from 1681 to 1787 reveals significant differences between rich and poor parishes in the strength of the preventive check. The urban poor respond to a price increase by dramatically decreasing fertility, while the fertility of the urban wealthy is virtually unaffected. An increase in prices is associated with relatively large increases in mortality, suggesting a strong positive check. However, little difference can be found between the rich and poor areas in the magnitude or timing of mortality responses to price variations." (SUMMARY IN FRE)

A technique for estimating life expectancy with crude vital rates

This paper describes a method of estimating life expectancy at birth on the basis of crude vital rates. The method is derived from stable population theory and it furnishes good estimates insofar as the current crude vital rates of a population are close to its intrinsic rates. This condition is generally met in closed populations which have not experienced sharp movements in fertility. The method is useful for estimating life expectancy in developing nations with good sample registration systems but for which information on age is of poor quality. It is also useful for estimating the movement of life expectancy in certain European nations in the period prior to regular census taking. There are a number of nations and regions in Europe for which long series of birth and death rates are available but for which census age counts are widely spaced.

Modeling and Forecasting Populations by Time Series: The Swedish Case

Time series analysis techniques are used to model and to forecast populations. An autoregressive (AR) and a moving average (MA) model, which seem to fit the population of Sweden very well, are found. Forecasts are calculated using both models and are compared with the forecasts obtained by other methods. This comparison is very favorable for the time series models. Although our study is confined to the mid-year population of Sweden, there are good reasons to expect that the technique can be successfully applied to other population parameters.

The demographic history of colonial New England

The central fact of the demographic history of early North America is rapid growth. Both Canada and the white population of the English colonies experienced increases of 2½ percent per year during the eighteenth century. Seventeenth-century rates, beginning from a low base and more influenced by immigration, were even higher. In contrast, the expansion of population in early modern Europe rarely exceeded 1 percent per annum over an extended period. Since Franklin and Malthus, interpretations of early American demography have centered on the high fertility associated with near universal marriage for women at a low average age. The extremely youthful population, high dependency ratio, and one of the largest mean census family sizes ever recorded all follow from the high level of fertility.