Longevity and the costs of reproduction in a historical human population.

It has been argued that the priority that natural selection places on reproduction negatively affects other processes such as longevity and the problem posed by this trade-off underlies the disposable soma theory for the evolution of human ageing. Here we examine the relationship between reproduction and longevity in a historical human population (the Krummhörn, north-west Germany 1720-1870). In our initial analyses, we found no support for the hypothesized negative effects of reproduction on longevity: married women who remained childless lived no longer than women who reproduced and women who had few children lived no longer than women who had many children. However, more detailed analyses in relation to socio-economic class revealed that the extent to which reproduction has an effect on longevity is a function of the level of economic deprivation. We found that, when possible sources of confound were controlled for (e.g. duration of marriage and amount of time spent in fecund marriage), there is an increasingly strong relationship between longevity and reproduction with increasing poverty.

Evolutionary ecology of human reproduction.

PIP: This article reviews the evolutionary ecology of human reproduction. The evolutionary ecology of human reproduction is defined as the application of natural selection theory to the study of human reproductive strategies and decision-making in an ecological context. The life history theory provides two crucial tools for evolutionary reproductive ecology. First, it identifies trade-off problems in reproductive investment. Second, the evolutionary physiology and psychology analyze the adaptive mechanism regulating reproduction. Because of the ecology of fecundity, fertility, child-care strategies, and differential parental investment resulted to advanced empirical insights. Also included in this article are the following three theoretical aspects for future improvement in evolutionary human reproductive ecology: a) the significance of and the interaction between different levels of adaptability (genetic, ontogenetic, and contextual) for the adaptive solution of reproductive problems; b) the dialectics of constraints and adaptive choices in reproductive decisions; and c) the dynamics of demographic change.^ieng

The impact of social status and migration on female age at marriage in an historical population in north-west Germany.

It has been suggested that parish-based reconstitution studies may underestimate the true age at marriage because they do not normally include data for emigrants who may be expected to behave differently from individuals who remain in their natal parishes. This study uses data from C18-19th parish registers of north-west Germany to estimate the difference in age at marriage between leavers and stayers. The difference is not significant for males; although that for females is significant, it is small and the consequence of failing to include migrants is likely to be negligible for most studies. However, it is shown that there is also an independent effect on age at marriage that is due to the woman's natal social (economic) status; historical demographic studies that ignore this dimension may risk confounding two different effects.

Resource competition and reproduction : The relationship between economic and parental strategies in the Krummhörn population (1720-1874).

A family reconstitution study of the Krummhörn population (Ostfriesland, Germany, 1720-1874) reveals that infant mortality and children's probabilities of marrying or emigrating unmarried are affected by the number of living same-sexed sibs in farmers' families but not in the families of landless laborers. We interpret these results in terms of a "local resource competition" model in which resource-holding families are obliged to manipulate the reproductive future of their offspring. In contrast, families that lack resources have no need to manipulate their offspring and are more likely to benefit from allowing their offspring to capitalize on whatever opportunities to reproduce present themselves.

How did the Krummhörn elite males achieve above-average reproductive success?

The wealthy elite males of nineteenth-century Krummhörn (Ostfriesland, Germany) achieved an above-average reproductive success. Membership in the elite class was determined from a list of the 300 richest men in the Ostfriesland district compiled by authorities in 1812. The main components establishing the link between cultural success and reproductive success are1.differences in the number of offspring owing to differences both in time spent in fecund marriage (mating success) and in rate of reproduction;2.differences in the probabilities of one's adult offspring marrying locally vs. emigrating unmarried owing to differential ability to allocate resources that enhance the "social placement" of adult offspring; and3.differences in the probability of total reproductive failure (lineage extinction). Contrary to what might be expected, infant survivorship was lowest amongst the richest families. We conclude that to a great extent females' reproductive decisions contribute to the greater reproductive success of the elite males.

Fitness of twinning.

On the basis of a family reconstitution of the rural Krummhörn population (Ostfriesland, Germany) of the eighteenth and nineteenth centuries, we pursued the question of to what extent the birth of twins contributed to the reproductive fitness of their mothers. The twinning rate was 16.2/1000; the secondary sex ratio among twins was 0.93, and it was 1.16 among their singleton siblings. Mothers of twins were older, had a longer generative life phase, and achieved higher age-specific fertility rates with shorter birth intervals. Parity effects on twinning tendency could not be detected. Twin maternities caused reproductive costs, namely, increased maternal, infant, and child mortality and obviously higher intrafamilial competition, because adult twins had fewer local marriage chances and to a higher degree were forced to emigrate. These reproductive disadvantages mean that the productivity of a male pair of twins, as measured by the number of live-born grandchildren, is clearly less than the productivity of a single boy. On the other hand, the birth of a female pair of twins led to more live-born grandchildren than the birth of a single girl. In sum, mothers of twins achieved greater reproductive success, with 13.5% more live-born grandchildren, than mothers of singletons only. The results are discussed against the background of Anderson's (1990) error hypothesis of twinning.

[Is the postmenopausal-age-at-death variable a fitness-maximizing reproductive strategy?]. / Ist das postmenopausale Sterbealter Variable einer fitnessmaximierenden Reproduktionsstrategie?

On the basis of the complete 18th century vital statistics available for 811 women from Ostfriesland (Germany), an attempt is made to examine the relationship between the postmenopausal age at death and the reproductive behaviour (reproductive effort and reproductive management). Although reproductive activities appeared to have a basically life-shortening effect in the population under study, this was independent of the amount of reproductive effort. The positive correlation reported in the literature to exist between the number of (surviving) children and the age at death was confirmed in our analysis; and it can partly be explained by the interference of another relationship, i.e. between the age at the last parturition and longevity. This correlation is interpreted as an expression of fitness-maximizing reproductive management. To this belongs the idea that the existence of unmarried children, i.e. the sub-optimal social position of one's descendants, had a life-lengthening effect on the women investigated. Whereas the effects found are largely statistically significant, they are on the whole very minor, so that we may surmise that only a small part of the total variance of the postmenopausal age at death can be interpreted as an expression of an adaptive reproductive strategy.