Status competition,inequality, and fertility: implications for the demographic transition

The role that social status plays in small-scale societies suggests that status may be important for understanding the evolution of human fertility decisions, and for understanding how such decisions play out in modern contexts. This paper explores whether modelling competition for status—in the sense of relative rank within a society—can help shed light on fertility decline and the demographic transition. We develop a model of how levels of inequality and status competition affect optimal investment by parents in the embodied capital (health, strength, and skills) and social status of offspring, focusing on feedbacks between individual decisions and socio-ecological conditions. We find that conditions similar to those in demographic transition societies yield increased investment in both embodied capital and social status, generating substantial decreases in fertility, particularly under conditions of high inequality and intense status competition. We suggest that a complete explanation for both fertility variation in small-scale societies and modern fertility decline will take into account the effects of status competition and inequality.     

More on the determinants of the fertility transition

Abstract

The economic approach to fertility is an application of the economics theory of consumer behavior. It is assumed that consumers of children are utility‐maximizers with stable preferences over time. Thus, changes in fertility are related to changes in household income and the “price” of children. One concern in this approach is that demographic changes are a product of changes in tastes rather than exogenous changes in economic factors such as the earning ability of women. In this paper, the effect of economic variables on the demand for children in the United States in 1950, 1960, 1970, and 1980 is examined. Support is provided for the hypothesis that the earning ability of women is an important determinant of fertility.     

More on the determinants of the fertility transition

The economic approach to fertility is an application of the economics theory of consumer behavior. It is assumed that consumers of children are utility-maximizers with stable preferences over time. Thus, changes in fertility are related to changes in household income and the "price" of children. One concern in this approach is that demographic changes are a product of changes in tastes rather than exogenous changes in economic factors such as the earning ability of women. In this paper, the effect of economic variables on the demand for children in the United States in 1950, 1960, 1970, and 1980 is examined. Support is provided for the hypothesis that the earning ability of women is an important determinant of fertility.     

Period and cohort dynamics in fertility norms at the onset of the demographic transition in Kenya 1978-1998

A characteristic of African pre-transitional fertility regimes is large ideal family size. This has been used to support claims of cultural entrenchment of high fertility. Yet in Kenya fertility rates have fallen. In this paper this fall is explored in relation to trends in fertility norms and attitudes using four sequential cross-sectional surveys spanning the fertility transition in Kenya (1978, 1984, 1989 and 1998). The most rapid fall in the reported ideal family size occurred between 1984 and 1989, whilst the most rapid fall in the total fertility rate occurred 5 to 10 years later, between 1989 and 1998. Thus these data, spanning the fertility transition in Kenya, support the traditional demographic model that demand for fertility limitation drives fertility decline. These data also suggest that the decline in fertility norms over time was partly a period effect, as the reported ideal family size was seen to fall simultaneously in all age cohorts, and partly a cohort effect, as older age cohorts reporting higher ideal family sizes were replaced by younger cohorts reporting lower ideal family sizes. These data also suggest that a new fertility norm of four children may have developed by 1989 and continued until 1998. This is consistent with, and perhaps could have been used to predict, the stall in the Kenyan fertility decline after 1998.     

Emotions and the intergenerational embodiment of social suffering in rural Bolivia

In this article, I take the embodied manifestations of distress across generations as the lens from which to illustrate the subtle articulations between the political restructuring of the Bolivian state and the private anxieties women experience under enduring political and economic instability. Emotions such as rage and sorrow generated by economic hardship, domestic violence, and social conflict played a fundamental role in how market- and working-class women perceived not only their own health problems but also many of the health problems that affected their infants. Mother's bodies and emotions are seen as the vectors through which gestating babies and breastfeeding infants develop transient and enduring ailments and debility.     

Impact of diet quality on demographic attributes in adult grasshoppers and the nitrogen limitation hypothesis

1. Various formulations of the nutrient stress hypothesis predict that insect herbivore populations will respond positively to increased nutrient quality of host plants, especially dietary nitrogen. Survival and reproduction by adult females of two grasshopper species [Acrididae;Melanoplus sanguinipes (Fabricius) and Phoetaliotes nebrascensis (Thomas)] were evaluated in response to defined diets that varied factorially in both total nitrogen (1–7%) and total soluble carbohydrate (4.3–26.7%). These grasshopper species coexist naturally but are typically shifted phenologically so that specific developmental stages normally encounter host plants of different nutritional quality under natural conditions. 2. Demographic responses by adult females of both species varied according to diet quality, but not in the same fashion. Diet quality affected survival significantly in P. nebrascensis but not in M. sanguinipes. Survival in P. nebrascensis was greatest on diets containing the lowest nitrogen concentrations; carbohydrate level had no effect. 3. Diet quality influenced reproduction significantly in both species. Egg production rate (eggs/day) in M. sanguinipes exhibited a negative linear response to increased carbohydrate, coupled with a significant quadratic response to nitrogen that reached a maximum at an intermediate level of about 4% total N. A significant quadratic response to total N for pod production rate (indicating the timing of reproduction) was also observed. Clutch size in M. sanguinipes exhibited a negative relationship with total carbohydrate in the diet, but no response to nitrogen. No interaction was observed between nitrogen and carbohydrate levels. For P. nebrascensis, response to diet quality was much weaker, with only a suggestive maximum at 4% total-N for both egg production rate (eggs/day) and clutch size (eggs/pod) and a suggestive linear response for pod production rate as carbohydrate level increased. Female body weight did not contribute to any reproductive response as a covariate variable. 4. Combined with a similar, previous analysis of demographic responses by the grass-feeding grasshopper, Ageneotettix deorum, these results challenge the ability to draw generalizations about host plant nutritional quality and grasshopper demographic responses. These three grasshopper species respond quite differently to defined diets that vary in total nitrogen and carbohydrate levels. Thus, although host plant quality can contribute significantly to grasshopper population responses, a uniform explanation is not likely.     

The effect of predator limitation on the dynamics of simple food chains

We investigate the influence of competition between predators on the dynamics of bitrophic predator–prey systems and of tritrophic food chains. Competition between predators is implemented either as interference competition, or as a density-dependent mortality rate. With interference competition, the paradox of enrichment is reduced or completely suppressed, but otherwise, the dynamical behavior of the systems is not fundamentally different from that of the Rosenzweig–MacArthur model, which contains no predator competition and shows only continuous transitions between fixed points or periodic oscillations. In contrast, with density-dependent predator mortality, the system shows a surprisingly rich dynamical behavior. In particular, decreasing the density regulation of the predator can induce catastrophic shifts from a stable fixed point to a large oscillation where the predator chases the prey through a cycle that brings both species close to the threshold of extinction. Other catastrophic bifurcations, such as subcritical Hopf bifurcations and saddle-node bifurcations of limit cycles, do also occur. In tritrophic food chains, we find again that fixed points in the model with predator interference become unstable only through Hopf bifurcations, which can also be subcritical, in contrast to the bitrophic situation. The model with a density limitation shows again catastrophic destabilization of fixed points and various nonlocal bifurcations. In addition, chaos occurs for both models in appropriate parameter ranges.     

Effects of the fertility transition on birth seasonality in the Netherlands

Synchronous with the decline in fertility that took place in the post-war period in the Netherlands, patterns of birth seasonality changed as well. In this paper seasonal fluctuations in fertility in the Netherlands are examined using population register data for the period 1952 to 2005. The peak in births has changed from spring to summer and subsequently to August/September, thereby shifting from the European to the American pattern. The seasonal shift can be attributed to parity-specific changes. Before the transition, birth seasonality did not differ much between the different parities. In the transition period from higher to low fertility, differences between parities increased which persist up to today. At present, the overall seasonality pattern is determined by first births. Moreover, birth seasonality varies by maternal age. The findings stimulate the discussion on the role of planning as a cause of birth seasonality.     

The effect of social isolation during juvenile period on the sexual arousal in adult rats

The effects of chronic postweaning social isolation combined with subsequent resocialization on the sexual arousal were studied in male rats with inherited stress-induced arterial hypertension (ISIAH strain) and in Wistar rats. Young males were isolated on the Day 21 of postnatal life for 6 weeks. Then they were kept in groups of 5. 4-month males underwent the partition test: a receptive female was introduced into the male's cage, but the male and the female were separated by a transparent partition. The number of approaches to the partition and total time spent near the partition during the test served as an index of sexual motivation. Hormonal component of sexual arousal was estimated by measuring plasma testosterone level. No interstrain differences in magnitude of the sexual arousal were observed. However, chronic social isolation during juvenile period caused a genotype-dependent diminution of sexual motivation in the adult male rats of both strains. The decrease of sexual motivation in ISIAH rats was more pronounced as compared to Wistar rats. Moreover, the social isolation during the juvenile period completely abolished the female-induced rise in plasma testosterone in ISIAH and Wistar male rats. Plasma corticosterone level was increased during the period of sexual arousal, but this rise of corticosterone was not affected by the social conditions during postweaning period.     

The effect of ancient DNA damage on inferences of demographic histories

The field of ancient DNA (aDNA) is casting new light on many evolutionary questions. However, problems associated with the postmortem instability of DNA may complicate the interpretation of aDNA data. For example, in population genetic studies, the inclusion of damaged DNA may inflate estimates of diversity. In this paper, we examine the effect of DNA damage on population genetic estimates of ancestral population size. We simulate data using standard coalescent simulations that include postmortem damage and show that estimates of effective population sizes are inflated around, or right after, the sampling time of the ancestral DNA sequences. This bias leads to estimates of increasing, and then decreasing, population sizes, as observed in several recently published studies. We reanalyze a recently published data set of DNA sequences from the Bison (Bison bison/Bison priscus) and show that the signal for a change in effective population size in this data set vanishes once the effects of putative damage are removed. Our results suggest that population genetic analyses of aDNA sequences, which do not accurately account for damage, should be interpreted with great caution.     

Cocoon predation on diprionid sawflies: the effect of forest fertility

Predation by small mammals is thought to be one of the main regulators of outbreaking sawfly species. It has been suggested that predation may be lower in poor and dryish forests, and this is the reason why outbreaks often begin from this type of environment. We studied experimentally how fertility of the forest site affects cocoon predation experienced by two sawfly species, the common pine sawfly Diprion pini (Linnaeus) and the European pine sawfly Neodiprion sertifer (Geoffroy). We applied a fertilization treatment to selected pine-dominated barren forest sites in Finland, and 2–4 years later monitored predation on the sawfly cocoons in fertilized and control areas. The results did not support the idea that forest fertility was related to cocoon predation. We also could not verify that small mammal abundance was related to fertility of the forest. The most obvious pattern we observed was that the two sawfly species differed dramatically in predation experienced. N. sertifer has its cocoon phase in mid-summer and experienced only moderate predation (37%) whereas D. pini, with its cocoon phase in autumn, suffered from very heavy predation (96%). Our observations suggest that if predation is important in controlling the population dynamics of the species, its impact depends more on the sawfly species and season than on the fertility of the forest site. Received: 1 March 1998 / Accepted: 25 May 1998     

The effect of "social stress" during rat pregnancy on the anxiety level of the progeny

Anxiety and locomotion were studied in offsprings of female rats subjected to everyday stress (one a day being displaced into another cage with pregnant rats) during the 3d stage of pregnancy. At the age of 1 month, the prenatally stressed rats had higher anxiety and lower locomotion in comparison with control animals. At the age of 3 month, the prenatally stressed females did not significantly differ from the control in the level of anxiety and locomotion, while the males demonstrated lower ambulation than the control animals.