Social and biological determinants of reproductive success in Swedish males and females born 1915–1929

Studying biological and social determinants of mortality and fertility provides insight into selective pressures in a population and the possibility of trade-offs between short- and long-term reproductive success. Limited data is available from post-demographic transition populations. We studied determinants of reproductive success using multi-generational data from a large, population-based cohort of 13,666 individuals born in Sweden between 1915 and 1929. We studied the effects of birthweight for gestational age, preterm birth, birth multiplicity, birth order, mother's age, mother's marital status and family socioeconomic position (SEP) upon reproductive success, measured as total number of children and grandchildren. We further tested the hypothesis that number of grandchildren would peak at intermediate family size, as predicted by some life history explanations for fertility limitation. Reproductive success was associated with both social and biological characteristics at birth. In both sexes, a higher birthweight for gestational age, a term birth and a younger mother were independently associated with a greater number of descendants. A married mother and higher family SEP were also associated with a greater number of descendants in males (but not in females), while higher birth order was associated with a greater number of descendents in females (but not males). These effects were mediated by sex-specific effects upon the probability of marriage. Marriage was also affected by other early life characteristics including birthweight, indicating how ‘biological’ characteristics may operate via social pathways. Number of grandchildren increased with increasing number of children in both sexes, providing no evidence for a trade-off between quantity of offspring and their subsequent reproductive ‘quality’.     

As the geneticist sees it

Abstract

Responses from 6,642 adolescents from forty‐six high schools in the United States were analyzed in a stepwise multiple regression to determine the independent as well as the combined effects of the variables (family size, birth order, and objective social class of father) on high‐school grade point average. Family size and birth order were not important. Contrary to other research findings, social class was of some importance. However, additional variables need to be introduced to explain grade point average.     

Gender,family configuration,and the effect of family background on educational attainment

Abstract

A comprehensive model of family influences on educational resemblance of siblings expands the traditional sibling pair model to a full sibship model in order to investigate how gender, gender composition of sibships, and a measure of ordinal position moderate the effect of social origins on educational attainments of siblings. One common family factor is sufficient to explain the variation of educational attainment among brothers and sisters. Although effects of social origin variables on brothers are larger than on sisters, the relative effects of measured social origins are virtually the same among sisters and brothers. The disparity between educational attainments of brothers and sisters persists across sex composition and family size. Ordinal position does not alter the effects of social origins on educational attainment nor does it directly affect educational attainment. Father's and mother's education are equally important for all siblings regardless of birth order, gender composition, and family size.     

Stillbirth pattern in an isolated mediterranean population: La Alpujarra, Spain

This study attempted to analyze the effect of several factors on the stillbirth pattern in a relatively isolated rural population, La Alpujarra (Spain), during the first half of the 20th century. The study was a retrospective analysis from a total sample of 2199 births to 525 mothers, allowing for birth year of mother, maternal age, parental inbreeding, family size, birth order, sex, single/twin delivery, and birth interval. Binomial probability distribution of stillbirths provided no evidence for any significantly increased risk in relation to family size. Analysis of covariance (ANCOVA) of stillbirth risk in affected families indicated a significant effect for sex of the child, parental consanguinity, and birth year of mother. Logistic regression showed increased risk in twin delivery and pregnancy order one, but not for birth order other than one. Multivariate analysis of variance (MANOVA) testing for differences between affected and unaffected families supported a temporal decrease of stillbirths during the period studied. Although the birth interval average was significantly shorter in affected families (p < 0.0001), this association did not hold, in a more detailed analysis, for individual intervals in these families (p = 0.20). There was no significant effect of maternal age on stillbirths in the whole sample or limited to first pregnancies. These results suggest that birth order one and twin delivery were the main determinants of the stillbirth pattern in La Alpujarra. Furthermore, our data indicate that the decline in stillbirth rate began before medical facilities for perinatal care became available, which was not until after 1950. The temporal decrease in stillbirth rates may therefore be related to an increasing social attention to deliveries rather than to prenatal care medical facilities.     

Sibling, family environment and ability correlates of adolescents' aspirations: ethnic group differences

Longitudinal data are used to examine relationships between sibling variables and adolescents' aspirations at different social status, family environment, and ability levels in a sample of 260 Anglo-Australian, 120 Greek, and 90 Southern Italian families. In this follow-up study of an earlier investigation, each family has a 16-year-old child and the analyses relate to these adolescents. The study shows that for the sample, sibling variables have modest associations with their educational and occupational aspirations, even after taking into account relationships involving social status, parents' associations, and ability. However, there are also ethnic group variations in the relations between the sibling variables and adolescents' aspirations. In particular, while sibship size tends not to be associated with aspirations within the different ethnic groups, birth order continues to show several significant relationships. The study suggests that there are differential relationships between birth order and educational and occupational aspirations for adolescents from different ethnic groups, even after taking into account the effect on aspirations of measures of ability and family environment.     

Social life factors affecting the mortality, longevity, and birth rate of total Japanese population: effects of rapid industrialization and urbanization

To expand upon the findings that lower mortality was found in Japanese urban areas in contrast to the Western model where in the US and Britain the risk of death was higher in metropolitan areas and conurbations, 22 social life indicators are examined among 46 prefectures in Japan in terms of their effect on age specific mortality, life expectancy, and age adjusted marriage, divorce, and birth rates. The effects of these factors on age adjusted mortality for 8 major working and nonworking male populations, where also analyzed. The 22 social life factors were selected from among 227 indicators in the system of Statistical Indicators on Life. Factor analysis was used to classify the indicators into 8 groups of factors for 1970 and 7 for 1975. Factors 1-3 for both years were rural or urban residence, low income and unemployment, and prefectural age distribution. The 4th for 1970 was home help for the elderly and for 1975, social mobility. The social life indicators were classified form 1 to 8 as rural residence in 1970 and 1975, urban residence, low income, high employment, old age, young age, social mobility, and home help for the elderly which moved from 8th place in 1970 to 1st in 1975. Between 1960-75, rapid urbanization took place with the proportion of farmers, fishermen, and workers declining from 43% in 1960 to 19% in 1975. The results of stepwise regression analysis indicate a positive relationship of urban residence with mortality of men and women except school-aged and middle-aged women, and the working populations, as well as life expectancy at birth for males and females and ages 20 and 40 years for males. Rural residence was positively associated with the male marriage rate, whereas the marriage rate for females was affected by industrialization and urbanization. High employment and social mobility were positively related to the female marriage rate. Low income was positively related to the divorce rate for males and females. Rural residence and high employment were positively related to the birth rate. The birth rate is higher in rural areas. Mortality of professional, engineering, and administrative workers was slightly lower than the total working population, while sales workers, those in farming, fishing, and forestry, and in personal and domestic service had significantly higher mortality. The mortality of the nonworking population was 6-8 times higher than sales, transportation, and communication, and personal and domestic service as well as the total population.     

Plain faces are more expressive: comparative study of facial colour,mobility and musculature in primates

Facial colour patterns and facial expressions are among the most important phenotypic traits that primates use during social interactions. While colour patterns provide information about the sender''s identity, expressions can communicate its behavioural intentions. Extrinsic factors, including social group size, have shaped the evolution of facial coloration and mobility, but intrinsic relationships and trade-offs likely operate in their evolution as well. We hypothesize that complex facial colour patterning could reduce how salient facial expressions appear to a receiver, and thus species with highly expressive faces would have evolved uniformly coloured faces. We test this hypothesis through a phylogenetic comparative study, and explore the underlying morphological factors of facial mobility. Supporting our hypothesis, we find that species with highly expressive faces have plain facial colour patterns. The number of facial muscles does not predict facial mobility; instead, species that are larger and have a larger facial nucleus have more expressive faces. This highlights a potential trade-off between facial mobility and colour patterning in primates and reveals complex relationships between facial features during primate evolution.     

Determinants of Low Birth Weight in Malawi: Bayesian Geo-Additive Modelling

Studies on factors of low birth weight in Malawi have neglected the flexible approach of using smooth functions for some covariates in models. Such flexible approach reveals detailed relationship of covariates with the response. The study aimed at investigating risk factors of low birth weight in Malawi by assuming a flexible approach for continuous covariates and geographical random effect. A Bayesian geo-additive model for birth weight in kilograms and size of the child at birth (less than average or average and higher) with district as a spatial effect using the 2010 Malawi demographic and health survey data was adopted. A Gaussian model for birth weight in kilograms and a binary logistic model for the binary outcome (size of child at birth) were fitted. Continuous covariates were modelled by the penalized (p) splines and spatial effects were smoothed by the two dimensional p-spline. The study found that child birth order, mother weight and height are significant predictors of birth weight. Secondary education for mother, birth order categories 2-3 and 4-5, wealth index of richer family and mother height were significant predictors of child size at birth. The area associated with low birth weight was Chitipa and areas with increased risk to less than average size at birth were Chitipa and Mchinji. The study found support for the flexible modelling of some covariates that clearly have nonlinear influences. Nevertheless there is no strong support for inclusion of geographical spatial analysis. The spatial patterns though point to the influence of omitted variables with some spatial structure or possibly epidemiological processes that account for this spatial structure and the maps generated could be used for targeting development efforts at a glance.     

Birth order, sibship size, and status in modern Canada

This paper investigates the possibility that birth order affects the degree to which individuals attain higher status. Humans give birth to a variable number of (usually) single offspring spaced one to many years apart, and continue to maintain contact with them for extended periods of time. The continued presence of older siblings, and arrival of younger ones, means that each child is reared in a different family environment. Research findings from the field of behavior genetics suggest that these differences have a significant impact on the development of individual differences between children in the same family. Although no two families are likely to be exactly the same, factors such as birth order remain constant across them, and may have similar influences. The present study examines the relationships between birth order, sibship size, and several variables thought to index future status attainment (status striving) in a random sample of Canadians. Firstborn children appear to be more status oriented than lastborns, and this effect is mediated by sibship size. While firstborn children are unaffected by the number of younger siblings they have, the status ambitions of youngest children decrease the more older siblings they have. Birth order effects on status attainment are not as strong as they are on status ambitions.     

Sibling and environment correlates of children's achievement: Sex group differences

Abstract

Regression surface analysis was used to examine associations between sibling variables and measures of academic achievement and intellectual ability at different levels of social status and family environment variables for girls and boys. The sample was 460 Anglo‐Australian families, each with an 11‐year‐old child. Family environments were defined by parents’ aspirations for their children and parents’ instrumental and affective orientations. Regression models included terms to account for possible linear, interaction, and curvilinear relations between sib size and birth order and measures of word knowledge, word comprehension, mathematics performance, and intellectual ability. The findings indicated that the sibling variables were poor predictors of children's cognitive performance. Typically, sib size and birth order were not related to children's academic performance at different levels of family environment scores.     

Birth order, sibling investment, and fertility among Ju/’Hoansi (!Kung)

Birth order has been examined over a wide variety of dimensions in the context of modern populations. A consistent message has been that it is better to be born first. The analysis of birth order in this paper is different in several ways from other investigations into birth order effects. First, we examine the effect of birth order in an egalitarian, small-scale, kin-based society, which has not been done before. Second, we use a different outcome measure, fertility, rather than outcome measures of social, psychological, or economic success. We find, third, that being born late in an egalitarian, technologically simple society rather than being born early has a positive outcome on fertility, and fourth, that number of older siblings and sibling set size are even stronger predictors of fertility, especially for males. Patricia Draper is a professor in the Department of Anthropology at the University of Nebraska. Her research interests are in cross-cultural human development, evolutionary theory, hunter-gatherer society, and comparative family organization. Raymond Hames is also a professor in the Department of Anthropology at the University of Nebraska. His research interests are in behavioral and evolutionary ecology, exchange systems, and tropical forest peoples.     

A test of the child replacement hypothesis: nineteenth century Massachusetts

Child mortality experiences may affect subsequent fertility of couples by exerting a physiological effect, influencing length of birth, interval, or a replacement effect, in which couples continue to procreate in an attempt to reach a desired number of surviving offspring. Where biological constraints are potentially important, however, it may be difficult to distinguish between purely physiological and purely behavioral components of the process regulating production. Natural spacing of births and onset of sterility may be affected by health and diet and prior childbearing and breastfeeding practices. Biological pressures can, in turn, be infuenced behaviorally both by social custom and individual choice. Studies of 126 families in 19th century Massachusetts show that reduction in infant mortality is not a prerequisite for onset of family limitation. Results for the study population did not exhibit a relationship between parity progression ratios and the experience of child mortality, consisten with the child replacement hypothesis. 1 factor involved may be the parent's expectations of more than the desired number of children because of imperfect contraceptive technology at the time. Preference for the sex of children also may weaken overall replacement effect, since the death of a child of "undesired" sex will not be replaced. The cohort age-specific fertility patterns indicate that a reduction in overall fertility level in the communities studied was parity-dependent and directed at stopping childbearing at some given range of family size. At any rate, parents are not passive participants in a natural regime of births and deaths. While child replacement may be present in some societies, it is relatively inefficient and perhaps infrequent.     

Factors associated with unfavourable birth outcomes in Kenya

Studies addressing factors associated with adverse birth outcomes have almost exclusively been based on hospital statistics. This is a serious limitation in developing countries where the majority of births do not occur within health facilities. This paper examines factors associated with premature deliveries, small baby's size at birth and Caesarean section deliveries in Kenya based on the 1993 Kenya Demographic and Health Survey data. Due to the hierarchical nature of the data, the analysis uses multilevel logistic regression models to take into account the family and community effects. The results show that the odds of unfavourable birth outcomes are significantly higher for first births than for higher order births. Furthermore, antenatal care (measured by frequency of antenatal care visits and tetanus toxoid injection) is observed to have a negative association with the incidence of premature births. For the baby's size at birth, maternal nutritional status is observed to be a predominant factor. Short maternal stature is confirmed as a significant risk factor for Caesarean section deliveries. The observed higher odds of Caesarean section deliveries among women from households of high socioeconomic status are attributed to the expected association between socioeconomic status and the use of appropriate maternal health care services. The odds of unfavourable birth outcomes vary significantly between women. In addition, the odds of Caesarean section deliveries vary between districts, after taking into account the individual-level characteristics of the woman.     

Genetic study on the mandibular molar size of rats

Tooth size is determined by genetic and environmental factors like other quantitative characters such as body weight and body height. However, the degree of the relative contribution of both factors to the determination of tooth size has not been well clarified. In order to study the genetic and environmental factors affecting tooth size, we carried out a diallel cross mating by the cohabitation of pairs of males and females among 10 strains of rats. The bucco-lingual widths of the first, second, and third molars of the right mandible were measured in each offspring of F1 population. The body weight was also measured as a parameter that might indicate systemic growth factor in connection with tooth development. The quantitative genetic analysis was performed based on Wearden's model (Heredity 19:669-680, 1964). As a result, the size of the first and the second molars was more significantly controlled by genetic effect than maternal effect, while maternal effect could not be ignored for the size of the third molar in addition to genetic effect. The genetic effect on body weight became greater with age, while the maternal effect showed its maximum influence upon the body weight around the weaning. It is concluded that the size of the molar teeth beginning to develop in the uterus and to be calcified just after birth was mainly controlled by genetic factor, and that the size of the molar teeth beginning to develop approximately after birth was mainly controlled by maternal effect affecting body weight at the same period.     

Seasonality of births and family characteristics in a Spanish population

The seasonality of births in the period 1871-1977 is studied in a rural north-western Spanish population. Based on a total sample of 11,695 birth registrations, temporal variation is analysed. For siblings, according to family reconstitution, the total family size, the legitimacy of the child, and birth order are considered. A coefficient of birth month dispersion is defined and estimated for each family. Intra-family variation is related to inter-family coefficients in order to determine whether the local seasonal pattern of births may be partly explained by family characteristics.     

Observations of a daytime birthing event in wild titi monkeys (Callicebus oenanthe): implications of the male parental role

Behaviors displayed during birth events, including prenatal, parturition, and postpartum periods, can give insight into caretaking roles in species in which the offspring is cared for by individuals other than the mother. Titi monkeys, genus Callicebus, exhibit a pair-bonded social system along with intense male care of offspring. Here, I report the first case of a birth seen in the wild in a group of Callicebus oenanthe, a little-known species in northern Peru, and describe infant care and development during the first few months after birth. Detailed behavior during the birth sequence as well as ad libitum data postpartum were recorded on nursing and infant care behaviors, including infant carrying, infant grooming, anogenital cleaning, protection, playing, and food sharing. In the 3 h preceding and during parturition, the male remained in contact with or in close proximity to the female (<1 m). The male licked and examined the newborn 3 min after parturition, carried the infant within 24 h after birth, was the main carrier of the infant, and was the predominant manual groomer of the infant during the first 4 months after birth. I argue that the male plays an integral role during the birth in order to establish his bond with the infant as well as reinforce infant care duties to the female and in predator vigilance. In light of various explanations for the exhibition of intense paternal care, I suggest that the male titi monkey provides infant care to release the female of these duties in order that she may spend more time foraging, thus potentially increasing the pair’s overall reproductive output.     

Menarche in Newcastle upon Tyne girls

Using data for 699 white girls from Newcastle upon Tyne, England, who were born in 1962, the authors examine the relationship between age at menarche and selected social and anthropometric variables. Factors considered include family size, birth order, father's occupation, birth weight, and height and weight at five years of age and at menarche (SUMMARY IN FRE, GER)     

Reproductive success in large populations: empirical measures and theoretical predictions of fertilization in the sea biscuit Clypeaster rosaceus

For organisms that free-spawn gametes into the environment, sperm limitation can be a major determinant of reproductive success. Previous tests of sperm limitation have been restricted to very small experimental populations. Here we test and then use a fertilization model to explore sperm limitation in large populations. Predictions of the fertilization model are compared with measures of dye diffusion and in situ fertilization of the sea biscuit Clypeaster rosaceus (Linnaeus). The model could not be rejected in either test. Then this model was used to simulate large-scale spawning events in a natural population of C. rosaceus. The results of our simulations indicate that both population size and population density are important to fertilization over a very large range (2 to over 250000 individuals), but we also found an important interaction between population size and density. The importance of high density was great in small populations but negligible in large populations. This result may provide insight into why aggregation during spawning is not universally seen in nature. Overall, results indicate that sperm limitation can both constrain reproductive success and mediate social behaviors in a wide range in population sizes.     

Social development during the first twenty weeks in the cotton-top tamarin (Saguinus o. oedipus)

Fourteen infant cotton-top tamarins from five captive family groups were studied during the first 20 weeks of life. We examined the roles of parents and of siblings of different ages as caregivers and as social companions for the infants, as well as the effects of group composition and group size on these roles. Parents and adult siblings played similar active roles in infant caregiving during the first few weeks after birth, with males showing a greater involvement than females. In groups without other offspring the two parents showed equal infant caregiving behaviour, whreas fathers carried more than mothers did in groups with offspring present. Although infants received more caregiving from males, they showed a preference for contact and proximity with their mothers. No sex differences were found in infant behaviour or in the direction of behaviour by caregivers toward infants. Twins showed greater amounts of both social and solitary play in weeks 15–20 than did singletons, and there was no effect of the number of older siblings on the amount of play shown by an infant.     

Early evidence for complex social structure in Proboscidea from a late Miocene trackway site in the United Arab Emirates

Many living vertebrates exhibit complex social structures, evidence for the antiquity of which is limited to rare and exceptional fossil finds. Living elephants possess a characteristic social structure that is sex-segregated and multi-tiered, centred around a matriarchal family and solitary or loosely associated groups of adult males. Although the fossil record of Proboscidea is extensive, the origin and evolution of social structure in this clade is virtually unknown. Here, we present imagery and analyses of an extensive late Miocene fossil trackway site from the United Arab Emirates. The site of Mleisa 1 preserves exceptionally long trackways of a herd of at least 13 individuals of varying size transected by that of a single large individual, indicating the presence of both herding and solitary social modes. Trackway stride lengths and resulting body mass estimates indicate that the solitary individual was also the largest and therefore most likely a male. Sexual determination for the herd is equivocal, but the body size profile and number of individuals are commensurate with those of a modern elephant family unit. The Mleisa 1 trackways provide direct evidence for the antiquity of characteristic and complex social structure in Proboscidea.