Differential Parental Investment Research Articles

A long-lasting, distant journey of a male griffon vulture informs on the success of differential parental investment.

A long-lasting, distant journey of a male griffon vulture informs on the success of differential parental investment.

Sex differences in diet and life conditions in a rural Medieval Islamic population from Spain (La Torrecilla, Granada): An isotopic and osteological approach to gender differentiation in al-Andalus.

Gender differentiation can influence the diet, physical activity, and health of human populations. Multifaceted approaches are therefore necessary when exploring the biological consequences of gender-related social norms in the past. Here, we explore the links between diet, physiological stress, physical activity, and gender differentiation in the Medieval Islamic population of La Torrecilla (Granada, Spain, 13th-15th century AD), by analyzing stable isotope patterns, stature, and long bone diaphyseal measurements. The sample includes 96 individuals (48 females, 48 males) classified as young and middle adults (20-34 and 35-50 years of age respectively). Diet was reconstructed through the analysis of δ13 C and δ15 N. Stature, humeral and femoral diaphyseal shape and product of diaphyseal diameters served as proxies of physiological stress and physical activity. Isotopic ratios suggest a substantial dietary contribution of C4 plants (e.g., sorghum, millet), a variable access to animal proteins, and no differences between the sexes. Sexual dimorphism in stature derives from a markedly low female stature. Long bone diaphyseal properties suggest that men performed various physically stressful activities, whereas women were involved in less physically demanding activities (possibly related to household work). Gender differentiation in La Torrecilla was expressed by a possibly differential parental investment in male versus female offspring and by culturally sanctioned gender differences in the performance of physical tasks. Diet was qualitatively homogenous between the sexes, although we cannot rule out quantitative differences. Our results shed new light on the effects of gender-related social norms on human development and lifestyle.

Child Wantedness and Low Weight at Birth: Differential Parental Investment among Roma.

Studies investigating child wantedness, birthweight and parental care are limited. This study assessed relationships of child wantedness, low birthweight and differential parental investment in a poor population of Serbian Roma. Data from the Multiple Indicator Cluster Survey round 5 for Roma settlements were used to account for the association between child wantedness and birthweight, and three measures of parental investment: breastfeeding practices, immunization of children and quality of mother–child interaction. The sample included 584 children aged 0–24 months. The child variables were gender, birth order, birthweight (low birthweight at <2500 g and normal birthweight at >2500 g) and whether the child was wanted, while maternal independent variables included age, literacy and household wealth. The results show that unwanted children were at greater risk of having low birthweight. After controlling for birthweight, child wantedness emerged as a predictor of breastfeeding practices and immunization status: Roma mothers biased their investment toward children who were wanted. The quality of mother–child interaction varied with the mother’s household wealth. Given the high rates of infant and child mortality among Roma, investments in children’s health should be prioritized within the family, where maternal bias in parental investment may contribute to their children’s health disparities.

The Effects of Mating Cues and Intrasexual Competition on Humor Production

The roles of mating cues and of intrasexual competition in humor production have not yet been assessed. Therefore, the present study explored the influence of implicit mating cues on humor enhancement. In two experiments involving 306 participants, using a priming methodology to examine sex differences and enhancement in humor production ability, participants were exposed to unattractive and attractive opposite-sex photographs, after which their humor production ability was rated. Studies differed in presentation durations of primes, and manipulation of intrasexual competition. The findings of Study 2 showed that, under conditions of intrasexual competition, men were superior to women in humor production ability and exhibited enhancement in humor ability following exposure to attractive women primes. The findings broaden the evolutionary cognitive framework in relation to sexual selection, differential parental investment, and social cognition.

Maternal mRNA input of growth and stress-response-related genes in cichlids in relation to egg size and trophic specialization

BackgroundEgg size represents an important form of maternal effect determined by a complex interplay of long-term adaptation and short-term plasticity balancing egg size with brood size. Haplochromine cichlids are maternal mouthbrooders showing differential parental investment in different species, manifested in great variation in egg size, brood size and duration of maternal care. Little is known about maternally determined molecular characters of eggs in fishes and their relation to egg size and trophic specialization. Here we investigate maternal mRNA inputs of selected growth- and stress-related genes in eggs of mouthbrooding cichlid fishes adapted to different trophic niches from Lake Tanganyika, Lake Malawi, Lake Victoria and compare them to their riverine allies.ResultsWe first identified two reference genes, atf7ip and mid1ip1, to be suitable for cross-species quantification of mRNA abundance via qRT-PCR in the cichlid eggs. Using these reference genes, we found substantial variation in maternal mRNA input for a set of candidate genes related to growth and stress response across species and lakes. We observed negative correlation of mRNA abundance between two of growth hormone receptor paralogs (ghr1 and ghr2) across all haplochromine cichlid species which also differentiate the species in the two younger lakes, Malawi and Lake Victoria, from those in Lake Tanganyika and ancestral riverine species. Furthermore, we found correlations between egg size and maternal mRNA abundance of two growth-related genes igf2 and ghr2 across the haplochromine cichlids as well as distinct clustering of the species based on their trophic specialization using maternal mRNA abundance of five genes (ghr1, ghr2, igf2, gr and sgk1).ConclusionsThese findings indicate that variations in egg size in closely related cichlid species can be linked to differences in maternal RNA deposition of key growth-related genes. In addition, the cichlid species with contrasting trophic specialization deposit different levels of maternal mRNAs in their eggs for particular growth-related genes; however, it is unclear whether such differences contribute to differential morphogenesis at later stages of development. Our results provide first insights into this aspect of gene activation, as a basis for future studies targeting their role during ecomorphological specialization and adaptive radiation.

Infant and childhood diet at the passage tomb of Alto de la Huesera (north‐central Iberia) from bone collagen and sequential dentine isotope composition

AbstractDuring the Late Neolithic (ca. 3500–2900 cal BC), the Rioja Alavesa region of north‐central Spain witnessed great demographic pressure and social unrest, manifested as widespread violent conflict. Drawing upon the ethnographic literature, it is possible that this situation impacted upon child‐rearing practices, both through food shortages and differential parental investment, favouring male infants. Here, carbon (δ13C) and nitrogen (δ15N) stable isotope measurements from bone collagen of 17 juveniles and from 163 serial microsamples of dentine from first and second molars of seven adults from the site of Alto de la Huesera are used to examine breastfeeding, weaning, and childhood diets. Bone and dentine collagen δ13C and δ15N isotope values both decrease from infancy to early childhood and increase slightly towards adolescence, but dentine provides a more time‐sensitive means of monitoring dietary changes. High δ13C and δ15N values compatible with exclusive breastfeeding are detected up to ca. 1 year, with a significantly shorter duration among males, suggesting differential sex‐related parental strategies from infancy. This is tentative given the small number of individuals being compared, but does suggest that further work would be worthwhile. A gradual decline in both δ13C and δ15N, compatible with the weaning process, is then observed up to ca. 4 years in both sexes. This delayed cessation of nursing is interpreted as a possible response to food shortage. With regard to postweaning patterns, shifts to lower δ13C and δ15N values in females at around age 9–11, and a general progressive increase in both isotope values from childhood to adolescence, are detected. These could be linked either with differential protein intake due to social age‐related nutritional practices or to physiological demand. The comparison between bone and dentine values shows differences between survivors and nonsurvivors in both isotopes, so that assessments based on deceased children may be biased by their potentially compromised health status.

Kin and birth order effects on male child mortality: three East Asian populations, 1716–1945

Human child survival depends on adult investment, typically from parents. However, in spite of recent research advances on kin influence and birth order effects on human infant and child mortality, studies that directly examine the interaction of kin context and birth order on sibling differences in child mortality are still rare. Our study supplements this literature with new findings from large-scale individual-level panel data for three East Asian historical populations from northeast China (1789–1909), northeast Japan (1716–1870), and north Taiwan (1906–1945), where preference for sons and first-borns is common. We examine and compare male child mortality risks by presence/absence of co-resident parents, grandparents, and other kin, as well as their interaction effects with birth order. We apply discrete-time event-history analysis on over 172,000 observations of 69,125 boys aged 1–9 years old. We find that in all three populations, while the presence of parents is important for child survival, it is more beneficial to first/early-borns than to later-borns. Effects of other co-resident kin are however null or inconsistent between populations. Our findings underscore the importance of birth order in understanding how differential parental investment may produce child survival differentials between siblings.

Maternal Behavior by Birth Order in Wild Chimpanzees (Pan troglodytes): Increased Investment by First-Time Mothers.

Parental investment theory predicts that maternal resources are finite and allocated among offspring based on factors including maternal age and condition, and offspring sex and parity. Among humans, firstborn children are often considered to have an advantage and receive greater investment than their younger siblings. However, conflicting evidence for this "firstborn advantage" between modern and hunter-gatherer societies raises questions about the evolutionary history of differential parental investment and birth order. In contrast to humans, most non-human primate firstborns belong to young, inexperienced mothers and exhibit higher mortality than laterborns. In this study, we investigated differences in maternal investment and offspring outcomes based on birth order (firstborn vs. later-born) among wild chimpanzees (Pan troglodyte schweinfurthii). During the critical first year of life, primiparous mothers nursed, groomed, and played with their infants more than did multiparous mothers. Furthermore, this pattern of increased investment in firstborns appeared to be compensatory, as probability of survival did not differ by birth order. Our study did not find evidence for a firstborn advantage as observed in modern humans but does suggest that unlike many other primates, differences in maternal behavior help afford chimpanzee first-borns an equal chance of survival.

Sex-specific traits in Common Tern Sterna hirundo chicks: associations with rearing environment, parental factors and survival

Offspring phenotypic variation has important consequences for the future survival, reproductive success and individual fitness of nestlings, but the sex-specific reproductive value and fitness returns for parents of this variation have only rarely been explored. We analysed twelve phenotypic traits of nestling Common Terns (Sterna hirundo) in relation to their sex, age and hatching date, and explored whether sexual differences in these traits were associated with the rearing environment and survival. In addition, we studied sex-specific differences in offspring phenotype related to parental factors, since the existence of sexual dimorphism may reflect differential parental investment. Bill–head length and mediated immune response varied in relation to offspring sex, with males showing larger values than females. Immune response was also affected by environmental (year), rearing (competition over 14 days old) and parental (clutch size) factors. None of the morphological, serological and immunological variables were associated with chick mortality, but female nestlings that did not survive had suffered longer periods of within-brood competition. Although some parental traits influenced offspring phenotype, sexual differences among nestlings did not vary in relation to parental age, mass or arrival date, which may imply that there is no great difference in cost between raising sons and raising daughters, and thus no adjustment of parental effort in relation to nestling sex. However, the evidence that immune response was higher for sons in larger clutches that were raised with siblings indicates a difference in the developmental strategies for sons and daughters, which may be related to their reproductive value. These results therefore provide evidence of certain pathways for parental sex allocation that may differentially affect sons and daughters.

High Incubation Investment of Females Paired to Attractive Males in Barn Swallows

Differential parental investment is the sexual selection process in which females that have acquired an attractive male invest relatively more in his offspring than females that are paired to an unattractive male. However, it is often difficult to distinguish between differential parental investment and compensation for a decrease in parental investment by an attractive mate. Using Barn Swallows Hirundo rustica gutturalis, in which males rarely participate in incubation, we investigated differential incubation investment of females. We made the following four observations: (1) Females participate in 94% of total nest attentiveness (time that eggs were incubated). (2) Female nest attentiveness was positively correlated with the ornamentation of their mates, the size of white spots in the tail, which is a measure of male attractiveness in this population. (3) Male nest attentiveness was not related to male ornaments. (4) Total nest attentiveness was positively correlated with the size of white spots in the tail. These results are consistent with differential parental investment, but not with compensation for a decrease in parental investment by a mate. Therefore, we conclude that female Barn Swallows that have acquired an attractive male invest differentially in incubation.

Does Biology Underlie the Oldest Profession? Prostitution and Sex Disparities in John Behavior

This study considers a biosocial explanation of why johns, the purchasers of commercial sex exchanges, are almost exclusively male. Trivers's theory of parental investment and sexual selection predicts that differential parental investment by biological sex will lead to divergent sex-based reproductive instincts. The sex bearing the larger parental investment will tend to be choosier, whereas the sex bearing the lesser investment will tend to be relatively indiscriminate and competitive for access to sexual resources. We hypothesized that men are more likely than women to offer objects of value in exchange for access to sexual resources. Using self-reports of sex-purchasing from Add Health data (N = 14,544), we found that maleness was a robust predictor of john behavior even after controlling for well-known criminogenic risk factors.

Sex differences in child nutritional and immunological status 5–9 years post contact in fringe highland Papua New Guinea

This study examines sex differences in vulnerability among children experiencing rapid culture change that may reflect distinct microecologies driven by differential parental investment and/or sex-specific life history strategies. Apparent female growth canalization may be a life history strategy favoring growth over maintenance but also may reflect sex-differentiated selection for resilience based on unequal treatment during early life. Stature, weight, and serum measures of C-reactive protein (CRP, an inflammation marker) and Epstein-Barr Virus antibodies (EBV, a humoral immune response marker) were collected longitudinally among children/adolescents ages 5-20 years (N = 65), 5-9 years after sustained contact in a fringe highland hunter-horticulturalist group from the Schrader Range in Papua New Guinea exhibiting male preference and sex-biased survival. It was hypothesized that girls would exhibit canalization, with better nutritional status than boys; lower maintenance investment would yield lower female immune activation; and because of differential survivorship, females would appear increasingly canalized as early conditions for girls worsened relative to boys. Girls had greater arm circumference z-scores than boys, less frequent stunting, and lower CRP despite high pathogen load. Average nutritional status for girls improved over time as the sex ratio became increasingly male biased and the condition of female infants reportedly worsened. Both canalization and survivorship effects were found. Although a life history perspective on female canalization can help explain developmental outcomes in populations undergoing rapid culture change amid adversity, possible sex differences in the strength of survivorship effects that select for resiliency should not be ignored.

Sex-specific behavior by a monomorphic seabird represents risk partitioning

The presence of sex-stereotyped behavior in monomorphic animals, where there are no sexual differences in form to account for sexual differences in function, is often attributed to intraspecific competition or to differential parental investment. The possibility that the use of different behavioral strategies by each parent may increase reproductive success for both partners through risk partitioning is seldom considered. We studied thick-billed murres (Uria lomvia), where the male exclusively feeds the offspring during the late chick rearing. During the period of biparental care, males fed on “risk-averse” prey (consistent across time and space; unitized risk = 0.29), whereas females fed on “risk-prone” prey (risk = 0.59). Males fed at night at 1 colony, during the day at 2 colonies, and there was no pattern at another colony. We suggest that these differences reflect the availability of risk-prone prey. Modeling suggested that mixed-risk pairs had higher success than “risky” or “riskless” pairs. Males accumulated reserves and reduced chick provisioning just prior to fledging. Thus, sex-specific patterns at 1 period (male-only care during postfledging) may have led to sex-specific patterns at earlier periods through the need for specialization in foraging habits and risk. We propose that risk partitioning may contribute to the prevalence of sex-specific behaviors in monomorphic animals and that patterns are likely context specific rather than species specific.

Differential parental investment in families with both adopted and genetic children

Stepchildren are abused, neglected and murdered at higher rates than those who live with two genetically related parents. Daly and Wilson used kin selection theory to explain this finding and labeled the phenomenon “discriminative parental solicitude.” I examined discriminative parental solicitude in American households composed of both genetic and unrelated adopted children. In these families, kin selection predicts parents should favor their genetic children over adoptees. Rather than looking at cases of abuse, neglect, homicide and other antisocial behavior, I focused on the positive investments parents made in their children as well as the outcomes of each child. The results show that parents invested more in adopted children than in genetically related ones, especially in educational and personal areas. At the same time, adoptees experienced more negative outcomes. They were more likely to have been arrested, to have been on public assistance and to require treatment for drug, alcohol or mental health issues. They also completed fewer years of schooling and were more likely to divorce. In adoptive families, it appears that “the squeaky wheel gets the grease.” Parents invest more in adoptees not because they favor them, but because they are more likely than genetic children to need the help. I conclude that discriminative parental solicitude differs in adoptive and step households because adoptive families generally result from prolonged parenting effort, not mating effort like stepfamilies.

Parental Investment in Children with Chronic Disease: The Effect of Child's and Mother's Age

Parents do not invest their resources in their children equally. Three factors which elicit differential parental investment are the parent's reproductive value, the child's reproductive value (RV), and the impact of the investment on the child (II). As the child matures, his RV increases while the II may decrease. This raises a question regarding the favored strategy of investment by child age. It was hypothesized that different categories of parental investment generate different age-based strategies. Emotional investment, such as maternal worrying for the child's health, was hypothesized to increase with the child's age, while direct care was hypothesized to decrease with the child's age. Both categories were hypothesized to increase with the mother's age at childbirth. 137 Israeli mothers of children with chronic neurological conditions reported levels of worrying for their child and levels of change in direct care. Maternal worrying about the child's health was positively associated with the child's age at diagnosis and the severity of his illness, and negatively associated with the time from diagnosis. An increase in direct care was positively associated with maternal age at childbirth and illness severity, and negatively associated with the time from diagnosis, and the duration of the marriage. Contrary to the hypothesis, the child's age had no effect on changes in direct care. It appears that in mothers of children with adverse neurological conditions, child and maternal age effect parental investment differently. While the child's age is related to maternal worrying about his health, the mother's age at childbirth is related to changes in direct care.

Sons or Daughters: a Cross-Cultural Study of Sex Ratio Biasing and Differential Parental Investment

Survivorship of children is dependent upon numerous variables, including the role that preferential treatment may play in biasing the birth and survival of sons and daughters across cultures. This study draws upon an evolutionary approach by examining a theory referred to as the “Trivers-Willard hypothesis” concerning condition-dependent sex allocation and differential parental investment. Previous research on humans concerning this hypothesis tends to be restricted to one cultural group and thereby limited in sample size. For this study, nationally representative household survey data collected by the Demographic and Health Surveys (DHS ) program across 35 countries was used to test biological, resource-oriented, and behavioral aspects affecting maternal condition, sex allocation, and parental investment in humans. The units of analysis for this study were the mothers and their lastborn child (N = 128,039 woman-child pairs). A series of hierarchical regressions were executed to empirically investigate the TW hypothesis in humans. Scales were developed for maternal socioeconomic resources (MSR), maternal biological condition (MBC), prenatal care for the lastborn child (PCL), and health-seeking for the lastborn child (HSL). MSR was measured by relative household economic status, woman's and partner's education, and residence in an urban/rural setting. MBC was defined by body mass index, pregnancy status and duration, and breast-feeding status. PCL was an index for type of prenatal care received, number of prenatal visits, and assistance during delivery of the lastborn child. Lastly, HSL measured indicators of treatment for diarrhea and immunizations received by the lastborn child. Across the 35 countries, the analyses did not support the Trivers-Willard hypothesis. However, there is evidence of regional and country level differences.

Differential Parental Investment in the Southwestern United States

The Trivers-Willard model (1973) predicts differential parental investment in children by sex and income; wealthier families will invest more in boys, while poorer families will invest more in girls. We investigated the TW Hypothesis in a sample of 103 six month old Tucson babies and their mothers. Hierarchical multiple regression equations were used entering baby's age, baby's sex, mother's age, male paternal commitment, a dichotomous poverty measure, per capita income, and four interaction terms, baby's sex by 1 ) mother's age 2) mother's education, 3) male paternal commitment, 4) poverty, and 5) per capita income. We included three dependent variables in successive regression equations; mother's attitudes towards ideal baby size for boy versus girl babies, weeks breast fed and the baby's weight at six months. These variables measure attitude, behavior, and physical outcomes. Poverty was a significant predictor of differential preference in ideal body size for boys versus girls; poor mothers preferred bigger baby girls. There was no evidence of differential preference in breast feeding. Education was also a significant predictor; but in the opposite direction than predicted by the TWH. Mothers with higher levels of education had heavier baby girls. Within Hispanics only, poverty was a significant predictor of sex-biased weight; poor mothers had heavier baby girls. This effect was not seen in Caucasians. These results provide mixed evidence for the Trivers-Willard model in a resource rich environment for humans.

Fitness consequences of variation in natural antibodies and complement in the Barn SwallowHirundo rustica

SummaryThe immune system and its component parts have evolved and are maintained due to the fitness benefits that hosts acquire in terms of parasite resistance. However, there are relatively few studies of the fitness consequences of natural variation in immunity in free‐living populations, mainly due to the complexity of the immune system and logistic problems of assessing immunity and fitness components.We quantified two aspects of humoral immunity in a population of Barn SwallowsHirundo rustica, natural antibodies and complement that constitute the first line of defence against parasites.The magnitude of both immune components increased during the breeding season.Very old adults had reduced levels of natural antibodies, providing evidence consistent with immuno‐senescence, while that was not the case for lysis. However, there was no evidence that survivors from one year to the next had stronger agglutination or lysis than nonsurvivors.Females with a second clutch had higher levels of natural antibodies than females that only had a single clutch, while males showed no differences. Annual fecundity of females decreased with natural antibody levels, that was not evident in males. Therefore, in females, natural antibody and complement levels are important predictors of vital rates.Tail length of male partners, but not of females, explained the variation in female natural antibodies and complement, while there was no similar effect in males. This pattern may have arisen from differential parental investment by females mated to the most attractive males.The abundance of four different ectoparasites was not predicted by either immune component.

Local Resource Enhancement and Sex‐biased Breastfeeding in a Caribbean Community

Quinlan, Robert J., Marsha B. Quinlan, and Mark V. Flinn. (2005) Local Resource Enhancement and Sex-biased Breastfeeding in a Caribbean Community. Current Anthropology, 46(3):471-480.

Parental Investment, Human Capital, and Cross-National Differences in Wealth

Economists have recently turned to family variables in search of explanations for why the economies of some countries grow more rapidly than others. This research tested the hypothesis that crossnational indicators of parental investment and human capital would be predictive of GNP per capita of 147 countries. Regression analysis found that close to two thirds of the variance in GNP was explained by parental investment factors (including total fertility rates, the adult sex ratio, polygyny, contraception, and school attendance rates). The effects of parental investment/human capital on wealth remained after controlling for climate, geography, endemic diseases, religion, and government policies, even though each of these was predictive of GNP. The data support the hypothesis that wealth differences between countries are associated with human capital differences accruing to differential parental investment.