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.
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The author has carried out a comparison between the female/male ratio (x 100) in different age groups in the Nordic countries and Greenland. The ratio was much the same, about 95, up to the age 45-50 years. But there were two exceptions, the Faroe Islands and Greenland. Here the excess of males aged 20-49 years was much higher than in the other countries. In Greenland for this was mainly due to an immigration of adult males, and the female/male ratio was 75.4. Some possible influences on the society are discussed.
About 50% of Swedish infants born in 1750 survived to have children themselves, and when they did they produced about 4 babies per family. In 1970 nearly all infants born could be expected to survive to adulthood, and about 2 babies were produced per family. This matching of the fertility rate to the childhood mortality rate could be the result of changes in the adult sex ratio.
Reports on adverse reactions to nitrofurantoin today are common in Sweden and constitute 10 to 12 percent of all incoming reports. We present an analysis of 921 reports of adverse reactions received by the Swedish Adverse Drug Reaction Committee during the period 1966--1976. The two largest groups consist of reports of acute pulmonary reactions (43 percent) and allergic reactions (42 percent). The remaining reports fall into any of four smaller groups, chronic pulmonary reactions, liver damage, blood dyscrasias or neuropathy. Acute pulmonary and acute allergic reactions in all aspects are very similar and carry the characteristics of an acute hypersensitivity reaction. The increasing number of reports--even in relation to sales figures--would be best explained by a continuous sensitization. Chronic pulmonary reactions (interstitial pneumonitis) afflict older patients, often after prolonged treatment with relatively small doses. We suggest that these reactions are elicited by a toxic mechanism. Seventy-one percent of all reactions were severe enough to cause the patient's hospitalization; only 1 percent was fatal. The risk of an adverse reaction varies with sex and age, increases with age and is higher in women than in men. The time has come for a re-evaluation of nitrofurantoin and its role in the treatment of urinary tract infections.
The prevalence of severe mental retardation (SMR) was studied in one of the 24 suburban municipalities in Stockholm. The study area had a high proportion of non-European nationals. The study population comprised 14138 children born between 1979 and 1992 who resided in this municipality on the census day, 31 December 1995. The total prevalence of SMR was 4.5 per 1000, being 3.7 per 1000 and 5.9 per 1000 in the European and in the non-European population, respectively. The majority of cases (66%) had a definite prenatal origin. Down syndrome was the cause in 20%. Six families (10%) had at least two children with SMR. It was concluded that the prevalence was higher than in previous Swedish studies. Many cases were attributed to genetic factors. Consanguineous marriages were assumed to be a factor of importance in the distribution of aetiologies. Demographic differences between areas in Sweden must be considered when planning habilitation services.
Alzheimer's disease (AD) is a neurodegenerative disorder which is characterized by a progressive loss of memory and the alteration of cognitive functions. At least three chromosomal segments have been associated with early-onset AD in genetic linkage studies. These results argue for a certain degree of heterogeneity in the genetic origin of some forms of AD, although environmental risk factors cannot be ruled out in late-onset AD. In this preliminary study, we analyzed the geographical distribution of the birth places of a sample of 235 AD cases born in a defined region of Quebec (Canada), between 1895 and 1935. We wished to test the hypothesis that risk factors acting at, or around birth place and time play a role in the etiology of AD. The field of study was divided into rural and urban areas. A reference population of live births was used to compute a measure of odds ratio (OR). The OR results showed a statistically significant excess of AD cases in the rural area as compared to the reference population. When stratified for sex, the OR results showed a global excess of female AD cases in both the rural and the urban areas. For men, only the urban area presented a statistically significant deficit. We also analyzed the structures of the genealogical kinships of the rural and urban sub-groups. Although AD cases from the rural sub-group were more closely related to each other than those from the urban one, removal of the kin pairs from the OR analysis seemed to have little effect on the rural/urban distribution of cases. Therefore, the OR results would not appear to be due primarily to a difference in the kinship structures of the two sub-groups. This could mean that some risk factors for AD afflict women more strongly than men, the effect being different depending on the urban or rural origin. However, potential biases such as a higher rate of report for women, differential migration between birth places or a differential mortality ratio between sexes could produce spurious results in the direction of what we have observed in this preliminary study.
The theory that natural selection has conserved mechanisms by which women subjected to environmental stressors abort frail male fetuses implies that climate change may affect sex ratio at birth and male longevity. Using time series methods, we find that cold ambient temperatures during gestation predict lower secondary sex ratios and longer life span of males in annual birth cohorts composed of Danes, Finns, Norwegians, and Swedes born between 1878 (earliest year with complete life tables) and 1914 (last birth cohort for which male life span can be estimated). We conclude that ambient temperature affects the characteristics of human populations by influencing who survives gestation, a heretofore unrecognized effect of climate on humanity.