Parent-offspring Conflict Theory Research Articles

Sibling aggression is surprisingly common and sexually egalitarian

Two well-supported generalizations from aggression research are that: a) people are less likely to commit homicide against close kin compared to non-kin, and b) females are less likely to engage in direct aggression than are males. Aggression between siblings, however, is somewhat more complicated than one might surmise from those two generalizations. Data from 3 studies collected using undergraduate and Prolific samples (N = 1640) reveal classic sex differences in direct aggression between non-relatives, but not between sisters and brothers. Whereas only a small minority of females have hit a friend or an acquaintance, the majority of females, like the majority of males, have hit a sibling. Although reputational aggression is substantially less likely between siblings than between friends or acquaintances, mild forms of direct aggression (such as hitting) are quite frequent between siblings. Discussion considers several possible limitations of the findings reported here and considers results in light of Trivers' theory of parent-offspring conflict.

The role of parent-offspring conflict in Shuar partner choice and marital practices

Previous research argues that female choice may not be as powerful an influence on the evolution of human mating preferences as once expected given the importance of parental choice in marital practices across cultures. Furthermore, much of the literature supporting this argument assumes that endorsed cultural norms reported in the ethnographic record accurately represent individuals' behaviors. Here, we argue that the roles of parent-offspring conflict and parental choice are more nuanced. We test predictions from parent-offspring conflict theory and illuminate three loci of conflict between parents and daughters over partner choice. Using data from over 10 years of fieldwork in Shuar communities, we demonstrate that endorsed norms do not reflect complete behavioral repertoires at the individual level. We conclude that analyzing individual behavior provides insight into (1) areas of parental-offspring conflict and (2) complementary aspects of female choice and parental choice.

The Theory of the Selfish Gene Applied to the Human Population

In a study drawing from both evolutionary biology and the social sciences, evidence and argument is assembled in support of the comprehensive application of selfish gene theory to the human population. With a focus on genes giving rise to characteristically-human cooperation (“cooperative genes”) involving language and theory of mind, one may situate a whole range of patterned behaviour—including celibacy and even slavery—otherwise seeming to present insuperable difficulties. Crucially, the behaviour which tends to propagate the cooperative genes may be “at cost” to the genes of some who may be party to the cooperation itself. Explanatory insights are provided by Trivers’ parent-offspring conflict theory, Lack’s principle, and Hamilton’s kin selection mechanism. A primary observation is that cooperation using language and theory of mind is itself interdependent with full human conceptualization of a world of objects and of themselves as embodied beings. Human capacities inhering in, or arising out of, the ability to cooperate are also responsible for a vitally important long-term process, the domestication of animals and plants. The approach illuminates the difference between animal and human sexual behaviour, and the emergence of kinship systems. Again, recent patterns of population growth become much more explicable. It is argued that the gene is the single controlling replicator; the notion of the meme as a second independent replicator is flawed.

Begging behavior as an honest signal of need and parent-offspring association during the postfledging dependency period.

Honest signaling mechanisms can function to appropriate care to hungry offspring and avoid misdirected care of unrelated offspring. Begging, the behavior by which offspring solicit food and parental care, may be an honest signaling mechanism for need, as well as association of parents and offspring. Roseate terns (Sterna dougallii) exhibit prolonged parental care during the postbreeding staging period, offering an ideal system in which to study begging as an honest signaling mechanism. We conducted focal sampling during two premigratory staging seasons (2014 and 2015) at Cape Cod National Seashore, Massachusetts, USA to determine whether postfledging tern begging behavior was an honest signal for need and parent–offspring association. Based on honest signaling theory, we expected begging behavior to be highest during times of high perceived need, and we expected to see a decrease in begging behavior as young terns became increasingly independent of the care‐giving parent. Also, we predicted that young terns would be more likely to beg at parents than nonparents. We found that young roseate terns begged at their parents more often than nonparents; however, they did not always beg at parents. Model predictions of begging probability showed a linear relationship between begging and time of day and date of season, such that begging increased with time of day and decreased with date of season, respectively. Our results provide evidence for honest parent–offspring interactions and are inconsistent with parent–offspring conflict theory but suggest that begging may play a complex role in postfledging parent–offspring interactions.OPEN RESEARCH BADGES This article has been awarded Open Data, Open materials Badges. All materials and data are publicly accessible via the Open Science Framework at https://doi.org/10.5281/zenodo.2656718.

Parent-offspring conflict over mate choice: An experimental study in China.

Both parents and offspring have evolved mating preferences that enable them to select mates and children-in-law to maximize their inclusive fitness. The theory of parent-offspring conflict predicts that preferences for potential mates may differ between parents and offspring: individuals are expected to value biological quality more in their own mates than in their offspring's mates and to value investment potential more in their offspring's mates than in their own mates. We tested this hypothesis in China using a naturalistic 'marriage market' where parents actively search for marital partners for their offspring. Parents gather at a public park to advertise the characteristics of their adult children, looking for a potential son or daughter-in-law. We presented 589 parents and young adults from the city of Kunming (Yunnan, China) with hypothetical mating candidates varying in their levels of income (proxy for investment potential) and physical attractiveness (proxy for biological quality). We found some evidence of a parent-offspring conflict over mate choice, but only in the case of daughters, who evaluated physical attractiveness as more important than parents. We also found an effect of the mating candidate's sex, as physical attractiveness was deemed more valuable in a female potential mate by parents and offspring alike.

Conflict or consensus? Synchronous change in mother–young vocal communication across weaning in the cat

Since parent–offspring conflict theory was first proposed, a number of studies in a range of mammalian species have questioned its importance, suggesting that coordination, rather than conflict, occurs during weaning. In this study we propose a set of behaviours for studying the development of the mother–offspring relationship: offspring separation calls and the corresponding maternal response, which can be used to describe the continually developing motivational changes in both parties accompanying weaning. We recorded and analysed separation calls of kittens of the domestic cat, Felis silvestris catus, during the first two postnatal months, and performed playback experiments to observe their mothers' behavioural response. Three different stimuli were played back: calls of the mothers' kittens at their correct age, calls of their kittens from an earlier age (1 week old) and a control sound. We found that kittens' separation calls changed in several respects across the 8 weeks of the study. After the first postnatal month, the number, intensity and fundamental frequency of calls declined markedly, while kittens' latency to call increased. In parallel, we found that during playback tests, mothers' willingness to return to the nest or reunite with their kittens decreased notably as the kittens approached weaning age. Since this decline was present even when mothers were played back the calls of their own kittens previously recorded at an earlier age, we conclude that the decline in responsiveness was not due to a change in the kittens' vocalizations, but rather to a change in the mothers' motivational state. Our findings support the view that weaning in the domestic cat is a well-synchronized process between mothers and offspring, at least under the favourable nutritional conditions of the present study.

Selfish Pups: Weaning Conflict and Milk Theft in Free-Ranging Dogs.

Parent-offspring conflict theory predicts the emergence of weaning conflict between a mother and her offspring arising from skewed relatedness benefits. Empirical observations of weaning conflict have not been carried out in canids. In a field-based study on free-ranging dogs we observed that nursing/suckling bout durations decrease, proportion of mother-initiated nursing bouts decrease and mother-initiated nursing/suckling terminations increase with pup age. We identified the 7th - 13th week period of pup age as the zone of conflict between the mother and her pups, beyond which suckling solicitations cease, and before which suckling refusals are few. We also report for the first time milk theft by pups who take advantage of the presence of multiple lactating females, due to the promiscuous mating system of the dogs. This behaviour, though apparently disadvantageous for the mothers, is perhaps adaptive for the dogs in the face of high mortality and competition for resources.

Parent-offspring conflict over family size in current China.

In China, the recent replacement of the one-child policy with a two-child policy could potentially change family ecology-parents may switch investment from exclusively one child to two. The parent-offspring conflict theory provides testable hypotheses concerning possible firstborn opposition toward further reproduction of their mother, and who wins the conflict. We tested the hypotheses that if there is any opposition, it will differ between sexes, weaken with offspring age and family resource availability, and affect maternal reproductive decision-making. Using survey data of 531 non-pregnant mothers of only one child from Xi'an (China), logistic regression was used to examine effects of age, family income, and sex on the attitudes of firstborn children toward having a sibling; ordinal regression was used to investigate how such attitudes affect maternal intention to reproduce again. Firstborns' unsupportive attitude toward their mothers' further reproduction weakened with age and was overall more frequent in low-income families. Sons' unsupportive tendency displayed a somewhat U-shaped relationship, whereas daughters' weakened with family income; consequently, sons were more likely than daughters to be unsupportive in high-income families, suggesting a tendency to be more demanding. Forty-nine percent of mothers supported by their firstborns intended to reproduce again, whilst only 9% of mothers not supported by firstborns had such an intention. Our study contributes to evolutionary literature on parent-offspring conflict and its influence on female reproductive strategy in modern human societies, and has also important implications for understanding fertility patterns and conducting interventions in family conflict in China.

Diluted Competition? Conflicts between Full- and Half-Siblings in Two Adult Generations

Sibling relations are typically close but ambivalent, including both altruism and competition. Full siblings are often assumed to exhibit more altruism and less competition than half-siblings. However, previous empirical findings indicate that this assumption may not hold for sibling conflicts in contemporary humans. We study self-reported occurrence of sibling conflicts among adults in two generations with nationally representative data from the Generational Transmissions in Finland surveys in 2012. Respondents represent an older generation (born between 1945 and 1950, n = 2,015) and their adult children (born between 1962 and 1993, n = 1,565). Based on kin selection and parent-offspring conflict theory we expect reports of any conflict to be more likely between full siblings than half siblings, between maternal half siblings than paternal half-siblings, and among the younger generation compared to the older generation. Results mostly support our hypotheses. Full siblings were more likely to report conflicts than were maternal and paternal half siblings in the younger generation. In the older generation, full siblings were more likely to report conflicts with paternal but not maternal half siblings. The younger generation was also more conflict-prone than the older. Results held when controlling for contact frequency, emotional closeness, unequal parental treatment, and several socioeconomic variables, as well as for within-family effects. Thus, although full siblings are typically closer and have more contact in adulthood than half siblings do, they also appear to have more conflicts. We suggest that this can be explained by diluted resource competition over parental investment between half siblings in societies with serial monogamy.

Viviparous placentotrophy in reptiles and the parent-offspring conflict.

In placentotrophic viviparous reptiles, pregnant females deliver nutrients to their developing fetuses by diverse morphological specializations that reflect independent evolutionary origins. A survey of these specializations reveals a major emphasis on histotrophy (uterine secretion and fetal absorption) rather than hemotrophy (transfer between maternal and fetal blood streams). Of available hypotheses for the prevalence of histotrophic transfer, the most promising derives insights from the theoretical parent-offspring conflict over nutrient investment. I suggest that histotrophy gives pregnant females greater control over nutrient synthesis, storage, and delivery than hemotrophic transfer, reflecting maternal preeminence in any potential parent-offspring competition over nutrient investment. One lizard species shows invasive ovo-implantation and direct contact between fetal tissues and maternal blood vessels, potentially conferring control over nutrient transfer to the embryo. Future research on squamates will benefit from application of parent-offspring conflict theory to the transition from incipient to substantial matrotrophy, as well as by testing theory-derived predictions on both facultatively and highly placentotrophic forms.

A long-term experimental study demonstrates the costs of begging that were not found over the short term.

Parent–offspring conflict theory predicts that begging behaviour could escalate continuously over evolutionary time if it is not prevented by costliness of begging displays. Three main potential physiological costs have been proposed: growth, immunological and metabolic costs. However, empirical evidence on this subject remains elusive because published results are often contradictory. In this study, we test for the existence of these three potential physiological costs of begging in house sparrow (Passer domesticus) nestlings by stimulating a group of nestlings to beg for longer and another group for shorter periods than in natural conditions. All nestlings were fed with the same quantity of food. Our study involves a long-term experimental treatment for begging studies (five consecutive days). Long-term studies frequently provide clearer results than short-term studies and, sometimes, relevant information not reported by the latter ones. Our long-term experiment shows (i) a clear effect on the immune response even since the first measurement (6 hours), but it was higher during the second (long-term) than during the first (short-term) test; (ii) evidence of a growth cost of begging in house sparrow nestlings not previously found by other studies; (iii) body condition was affected by our experimental manipulation only after 48 hour; (iv) a metabolic cost of begging never previously shown in any species, and (v) for the first time, it has shown a simultaneous effect of the three potential physiological costs of begging: immunocompetence, growth, and metabolism. This implies first, that a multilevel trade-off can occur between begging and all physiological costs and, second, that a lack of support in a short-term experiment for the existence of a tested cost of begging does not mean absence of that cost, because it can be found in a long-term experiment.

Variation in social structure alters queen body mass and productivity in the desert seed-harvester ant Messor pergandei

Parent–offspring conflict theory predicts conflict between parents and their offspring over per-offspring resource investment. Across the range of the desert seed-harvester ant, Messor pergandei, daughter queens use three different social strategies during colony founding that are expected to alter the optimal level of parental investment. To test whether social strategy variation is associated with shifts in body mass, we surveyed queen live mass over 3 years at 25 sites that spanned the range of behavioral strategies and founding group sizes. To test whether reduction in parental investment into individual offspring negatively impacts their productivity, queens were individually isolated and allowed to produce a single worker cohort under common garden conditions. Queen live mass was highly variable, from 24 mg on average at the site with the lightest queens to 1.5 times that size, 37 mg, at the site with the heaviest queens. As predicted by parent–offspring conflict over investment, solitary colony founding sites contained the heaviest queens, followed by secondary monogyny. Polygynous queens were lightest, with a strong negative relationship between group size and live mass. Reductions in body mass had a negative effect on queen productivity across all queen social types; however, queens from sites where queen–queen aggression is typical were significantly more efficient at brood rearing, resulting in lower mass loss during founding per unit offspring biomass. This may represent an adaptation to queen competition to gain a strength advantage over potential rivals.

Medical, ethical and personal dimensions of parent-offspring conflicts

Medical, ethical and personal dimensions of parent-offspring conflicts

Selfish mothers? An empirical test of parent-offspring conflict over extended parental care

Parent-offspring conflict (POC) theory is an interesting conceptual framework for understanding the dynamics of parental care. However, this theory is not easy to test empirically, as exact measures of parental investment in an experimental set-up are difficult to obtain. We have used free-ranging dogs Canis familiaris in India, to study POC in the context of extended parental care. We observed females and their pups in their natural habitat for the mother's tendency to share food given by humans with her pups in the weaning and post-weaning stages. Since these dogs are scavengers, and depend largely on human provided food for their sustenance, voluntary sharing of food by the mother with her pups is a good surrogate for extended parental care. Our behavioural observations convincingly demonstrate an increase of conflict and decrease of cooperation by the mother with her offspring over given food within a span of 4–6 weeks. We also demonstrate that the competition among the pups in a litter scales with litter size, an indicator of sib–sib competition.

Magpies do not desert after prolonging the parental care period: an experimental study

Parent–offspring conflict theory predicts that offspring desertion would be adaptive for parents when the fitness costs related to invest ment in the current brood exceed the expected fitness benefits. In several seabirds, a fixed parental care period has been observed, and a preprogrammed fixed parental care period could be a general life-history trait evolved because of parent–offspring conflict. A recent study suggested that this could also be the mechanism by which hosts could discriminate against brood parasitic chicks that need longer care periods, by abandoning a brood when the parental care period passed the one typically needed by their own brood (i.e., discrimination without recognition). Here, we experimentally tested if a fixed parental care period also existed in magpies (Pica pica), the primary host of the great spotted cuckoo (Clamator glandarius). None of the experimentally prolonged magpie broods were deserted, and neither were any of the control or shortened broods. These results suggest that a preprogrammed parental care period is not a general trait in birds and support the idea that brood parasitism could be a selective pressure for optimal (short) parental care periods to evolve, but only in species where brood parasitic nestlings need a longer care period than host nestlings (which was not the case for the great spotted cuckoo). Furthermore, nestlings reared by parents with prolonged parental care period showed a slower development. Increasing provisioning costs, reduced sensitiveness to begging signals, or sexual conflict could cause this result, upholding parental care periods as a challenging matter of research.

Parent-Offspring Conflict and the Persistence of Pregnancy-Induced Hypertension in Modern Humans

Preeclampsia is a major cause of perinatal mortality and disease affecting 5–10% of all pregnancies worldwide, but its etiology remains poorly understood despite considerable research effort. Parent-offspring conflict theory suggests that such hypertensive disorders of pregnancy may have evolved through the ability of fetal genes to increase maternal blood pressure as this enhances general nutrient supply. However, such mechanisms for inducing hypertension in pregnancy would need to incur sufficient offspring health benefits to compensate for the obvious risks for maternal and fetal health towards the end of pregnancy in order to explain why these disorders have not been removed by natural selection in our hunter-gatherer ancestors. We analyzed >750,000 live births in the Danish National Patient Registry and all registered medical diagnoses for up to 30 years after birth. We show that offspring exposed to pregnancy-induced hypertension (PIH) in trimester 1 had significantly reduced overall later-life disease risks, but increased risks when PIH exposure started or developed as preeclampsia in later trimesters. Similar patterns were found for first-year mortality. These results suggest that early PIH leading to improved postpartum survival and health represents a balanced compromise between the reproductive interests of parents and offspring, whereas later onset of PIH may reflect an unbalanced parent-offspring conflict at the detriment of maternal and offspring health.

The Origins and Effects of Filial Piety (Xiao 孝): How Culture Solves an Evolutionary Problem for Parents

Abstract Parent–offspring conflict theory hypothesizes that interests of offspring and parents are asymmetrical in key contexts including the offspring’s mating strategies and mate preferences. Evidence supports this hypothesis and documents these asymmetries in humans. However, offspring in East Asia have mate preferences and mating strategies that are in significantly greater harmony with their parents’ preferences about their mating choices as compared with offspring elsewhere in the world. The paper hypothesizes that the Confucian virtue of filial piety (xiao 孝) was designed and disseminated in order to benefit parents by enabling them successfully to extract more resources out of their offspring than is expected given either data from parent–offspring conflict theory or data from cross-cultural studies of mate preferences and mating strategies. The results of this project mark an early step in building a stable interdisciplinary platform from which to more accurately observe and appraise the unappreciated, awe-inspiring influence of Confucianism.

Parent–Offspring Conflict over the Transition to Independence in Nicrophorus vespilloides: Parental Chemical Cues and Offspring Begging

AbstractIn species where parents provide their offspring with food, the offspring must undergo a transition from nutritional dependency to independence. Parent–offspring conflict theory predicts that the optimal timing for this transition will differ between parents and offspring and that the realised timing depends on each party’s ability to control the transition. The burying beetle Nicrophorus vespilloides is an excellent species for studying conflict over the transition to independence; the larvae beg for pre‐digested carrion from their parents until they cease begging around 72 h after hatching. The cessation of begging is not associated with changes in parental behaviour, suggesting that the transition is mostly under offspring control. However, recent work has demonstrated that caring parents express distinct chemical cues that stimulate larval begging, the expression of which varies between breeding and non‐breeding beetles, suggesting that parents might exert control over the transition to independence by altering these cues throughout development. If so, we predict that begging larvae should behave differently towards parental chemical cues from different stages of development and that larvae of different ages should behave similarly towards parental chemical cues from the same stage of development. We found no evidence for either prediction: begging larvae did not behave differently towards parental chemical cues from different stages of development, and larvae of different ages still behaved differently towards parental chemical cues from the same stage of development. Our results provide no support for the hypothesis that parents can control the transition to nutritional independence by altering their chemical profiles.

Maternal age, investment, and parent–child conflict: A mediational test of the terminal investment hypothesis.

Drawing on the evolutionary terminal investment hypothesis and Trivers' (1974) parent-offspring conflict theory, we advance and evaluate a mediational model specifying why and how maternal age, via mating effort and parental investment, affects mother-child conflict. Data from a longitudinal study of 757 families indicate that (a) older maternal age predicts lower mating effort during the child's first 5 years of life, and (b) thereby, higher maternal investment in middle childhood when the child is around 10 years old. (c) Higher maternal investment, in turn, forecasts less child-perceived mother-child conflict in adolescence (age 15). These results proved robust against theoretically relevant covariates (family resources, parity, maternal education, and maternal personality characteristics) and in the context of an autoregressive model. Study limitations are noted and results are discussed in terms of the unique contributions of an evolutionary perspective to the determinants-of-parenting literature.

Flexibility in the duration of parental care: zebra finch parents respond to offspring needs

Parent–offspring conflict theory posits that parents and offspring differ in the optimal duration of parental care. Accordingly, the timing of the termination of parental care could be contested between parents and offspring. The outcome of this conflict might be related to the degree of parental sensitivity to offspring demand. By cross-fostering zebra finch, Taeniopygia guttata, chicks of different ages among breeding pairs, we examined whether parents continue parental behaviour for a fixed time period, or are sensitive to offspring age. Parents provisioned chicks in the nest for longer when they received younger foster chicks and for less time when they received older foster chicks. All chicks fledged and became independent at the same age. Our results show that zebra finch parents extend the period of parental care in response to protracted demands from their brood.