Parent-offspring communication is widely regarded as having evolved to provide the parent with honest information about the hunger state of its offspring, thus enabling it to mediate conflict over resource allocation between parents and offspring. The conflict is caused by the offspring benefitting from receiving more care than the parents are selected to provide due to the costliness of care. I studied the role of parent-offspring communication as a mediator for the conflict in the burying beetle Nicrophorus vespilloides. The burying beetle is an excellent study system for this question, as the larvae, that are raised on carcasses of small vertebrates and cared for by both the male and the female beetle, beg for food from their parents with highly distinguishable begging displays. First, I examined whether offspring adjusted their begging to different classes, or individual adult beetles. I found that while the larvae did not discriminate between male and female beetles, they adjusted their care to cues indicating individual recognition of adults. Second, I tested whether begging was based on offspring size at egg stage, and found no indication that offspring adjusted their begging to improve their innate quality. Third, I examined whether parental response to begging exhibits behavioural plasticity when the internal clock for the timing of reproduction for the parent, and the demand from the larvae do not meet. I found that the parents adjusted their care based on the amount of begging exhibited by the larvae. Fourth, I investigated whether parental adjustment of care based on offspring begging incurs a reproductive cost to them. I found that the females paid a cost in fecundity, but not in the number of dispersing larvae or their own survival. My original contribution to knowledge is therefore to show through these four studies, that offspring begging is adjusted based on parental cues, and can directly affect proximate parental behaviours, and also incurs a reproductive cost to their future reproductive success, thus providing more experimental evidence for the importance of parent-offspring communication, and its implications to the evolution of parental care.

Parent-offspring conflict theory (POCT) has been underutilized by researchers interested in family relationships. The goal of these three manuscripts is to help remedy this problem.Manuscript one presents POCT in its original formulation and more recent developments. The theory is described and explained and four topical areas of human development are discussed in terms of how POCT has been applied and how the theory can help inform future research.Manuscript two tests hypotheses derived from POCT about mother-adolescent conflict. This study showed that coresidence with a younger half sibling significantly incremented conflict between mothers and their children. This effect was not explained by SES, maternal depression, number of children in the household, or stepfather presence. In addition, children in younger half sibling households demonstrate elevated levels of conflict compared to families with a younger full sibling indicating that this effect is not an artifact of coresidence with a younger sibling. Presence of a younger half sibling also partially mediated the relationship between biological parental disruption and mother-child conflict.Manuscript three sought to extend on the findings from manuscript two by examining how different family contexts affect trajectories of mother-child conflict across adolescence. A piecewise growth model was implemented to estimate linear conflict trajectories from early to mid and from mid to late adolescence. Results indicated that conflict tends to increase from early to mid adolescence but remain constant from mid to late adolescence, that biological parental disruption did not differentiate trajectories of conflict, nor did living with a stepfather. In addition, despite a large difference in regression coefficients between families with and without a younger half sibling, younger half sibling status did not differentiate conflict trajectories from early to mid adolescence. Families did differ in their trajectories from mid to late adolescence with younger half sibling families showing a reduction in conflict over this time period. Inclusion of family level covariates effectively nullified all significant results. Results are discussed in the context of parent-offspring conflict theory. It is concluded that a larger sample with more diverse family types is needed to achieve sufficient power for additional analyses and future research.

O presente trabalho se propõe a compreender a variabilidade cultural humana em relação à organização da família por meio das teorias darwinianas da seleção natural e da seleção sexual, e se encontra baseado em evidências vindas da comparação de dados etnográficos. Pretende-se demonstrar que existe uma alteração marcante no comportamento de todos os envolvidos nas relações familiares quando mudam as regras de herança. Essas alterações assim ocorrem porque as regras de herança direcionam o Investimento Parental Masculino (MPI), ora ao sobrinho, ora ao filho. A hipótese apresentada é a de que a variação do MPI modifica de maneira compreensível e previsível as relações familiares em organizações matrilineares e patrilineares. A prova da hipótese será feita por meio da aplicação do método intercultural com pesquisa etnográfica nos bancos de dados do HRAF, e utilizando-se da amostra PSF. Os resultados do presente trabalho indicarão que em sociedades em que o tio tem uma relação afetuosa com seu sobrinho, o marido espanca a mulher; e quando o pai se relaciona de maneira indulgente e amigável com seu filho, irmãos e irmãs se evitam, alinhando esses fatos de maneira que possam ser coerentemente entendidos com a teoria sociobiológica. A riqueza cultural, o sem número de costumes, as tradições, os tabus, as normas explícitas ou ocultas, os aparatos de coerção de toda sorte, as regras sobre herança, casamento, dote, preço da noiva, divisão de trabalho, enfim, todas as regras observadas em todos os agrupamentos humanos podem ser explicadas à luz das seguintes teorias: a) da “seleção de consangüíneos" (Hamilton, 1963), b) do “altruísmo recíproco" (Trivers, 1971), c) do “investimento parental e seleção sexual" (Trivers, 1972), e d) do “conflito entre prole e parentais" (Trivers, 1974). / The present work proposes to account for cultural variability in connection to human family organization, through Darwin’s theories of natural selection and sexual selection. It is also founded on evidence based on the comparison of ethnographic data of diverse human societies. It intends to demonstrate that there is a significant alteration in the behavior of family members when the rules of inheritance of wealth change. These alterations are triggered because the rules of inheritance dictate the MPI – Male Parental Investment – sometimes in the nephew and sometimes in the son. The hypothesis is that this variation in MPI (male investment in either the nephew or the son) modifies family relations in matrilineal and patrilineal organizations in a predictable manner. The role played by MPI in determining family tensions will be shown by applying cross cultural analysis to the data obtained from HRAF (Human Relations Area Files), using PSF (Probability Sample Files). The results of the present work show that societies in which the uncle’s relation with his nephew is affectionate, the husband beats the wife; on the other hand, when the father’s relation with his son is indulgent and friendly, brother and sister avoid each other. This variability of behavior can be coherently explained by sociobiological theory. Cultural wealth: the innumerable customs, the traditions, the taboos, the manifest and hidden norms, the apparatus of coercion, the rules of inheritance, marriage, dowry, bride price, the division of labor, in short, all the rules observed in all human groups can be explained in the light of the following theories: a) ‘kinship selection’ (Hamilton, 1963); b) ‘reciprocal altruism’ (Trivers, 1971; Axelrod, 1981); c) ‘parental investment and sexual selection’ (Trivers, 1972); and d) ‘parentoffspring conflict’ (Trivers, 1974).

O presente trabalho se propõe a compreender a variabilidade cultural humana em relação à organização da família por meio das teorias darwinianas da seleção natural e da seleção sexual, e se encontra baseado em evidências vindas da comparação de dados etnográficos. Pretende-se demonstrar que existe uma alteração marcante no comportamento de todos os envolvidos nas relações familiares quando mudam as regras de herança. Essas alterações assim ocorrem porque as regras de herança direcionam o Investimento Parental Masculino (MPI), ora ao sobrinho, ora ao filho. A hipótese apresentada é a de que a variação do MPI modifica de maneira compreensível e previsível as relações familiares em organizações matrilineares e patrilineares. A prova da hipótese será feita por meio da aplicação do método intercultural com pesquisa etnográfica nos bancos de dados do HRAF, e utilizando-se da amostra PSF. Os resultados do presente trabalho indicarão que em sociedades em que o tio tem uma relação afetuosa com seu sobrinho, o marido espanca a mulher; e quando o pai se relaciona de maneira indulgente e amigável com seu filho, irmãos e irmãs se evitam, alinhando esses fatos de maneira que possam ser coerentemente entendidos com a teoria sociobiológica. A riqueza cultural, o sem número de costumes, as tradições, os tabus, as normas explícitas ou ocultas, os aparatos de coerção de toda sorte, as regras sobre herança, casamento, dote, preço da noiva, divisão de trabalho, enfim, todas as regras observadas em todos os agrupamentos humanos podem ser explicadas à luz das seguintes teorias: a) da “seleção de consangüíneos” (Hamilton, 1963), b) do “altruísmo recíproco” (Trivers, 1971), c) do “investimento parental e seleção sexual” (Trivers, 1972), e d) do “conflito entre prole e parentais” (Trivers, 1974). / The present work proposes to account for cultural variability in connection to human family organization, through Darwin’s theories of natural selection and sexual selection. It is also founded on evidence based on the comparison of ethnographic data of diverse human societies. It intends to demonstrate that there is a significant alteration in the behavior of family members when the rules of inheritance of wealth change. These alterations are triggered because the rules of inheritance dictate the MPI – Male Parental Investment – sometimes in the nephew and sometimes in the son. The hypothesis is that this variation in MPI (male investment in either the nephew or the son) modifies family relations in matrilineal and patrilineal organizations in a predictable manner. The role played by MPI in determining family tensions will be shown by applying cross cultural analysis to the data obtained from HRAF (Human Relations Area Files), using PSF (Probability Sample Files). The results of the present work show that societies in which the uncle’s relation with his nephew is affectionate, the husband beats the wife; on the other hand, when the father’s relation with his son is indulgent and friendly, brother and sister avoid each other. This variability of behavior can be coherently explained by sociobiological theory. Cultural wealth: the innumerable customs, the traditions, the taboos, the manifest and hidden norms, the apparatus of coercion, the rules of inheritance, marriage, dowry, bride price, the division of labor, in short, all the rules observed in all human groups can be explained in the light of the following theories: a) ‘kinship selection’ (Hamilton, 1963); b) ‘reciprocal altruism’ (Trivers, 1971; Axelrod, 1981); c) ‘parental investment and sexual selection’ (Trivers, 1972); and d) ‘parentoffspring conflict’ (Trivers, 1974).