Abstracts

TITLES

Stuart Birks – Massey University: Unanticipated consequences of changed relationship legislation

Russell Bonduriansky – University of New South Wales: Can sexual conflict theory shed light on the modern marketplace?

Jenny Brown – The Family Systems Institute & University of New South Wales: Good Cop / Bad Cop: the parenting soft hard split as an adaptation

Andrea Camperio Ciani – University of Padova: Sexually antagonistic selection explains male homosexuality evolutionary conundrum

Murshed Chowdhury – King’s University College at Western University: Remitting Behavior of Indian and Chinese Immigrants: Evidence from Canadian Micro-data

Martin Daly – University of Missouri: Discrimination against stepchildren: why so variable?

Henry Dixson – The Australian National University: The Ontogeny of Third Party Punishment

Barnaby Dixson – University of New South Wales: Social support from androphilic kin predicts augmented preferences for masculine mates among Samoan women

Jasper Duineveld – University of Western Sydney: The implicit and explicit motives of the Dark Triad

Will Feeney – Australian National University: Correlated Evolution of Brood Parasitism and Cooperative Breeding in Birds

Hayley Fisher – University of Sydney: The economic consequences of relationship breakdown: income shocks and the extended family

Gigi Foster – University of New South Wales and Paul Frijters – University of Queensland: An Economic Model of Power, Gender, and the Value of Singlehood

Julián Garcia – Max Planck Institute for Evolutionary Biology: Evolution of cooperation: reciprocity and population structure

Amany Gouda-Vossos – University of New South Wales: Sex-Differences in Social Cues that Modify Perceived Status

Simon Griffith – Macquarie University: Conflict and cooperation in socially monogamous birds

Dana Hanna – Australian National University: The Family Constellation, Home Learning Activities and the Progress of Cognitive Ability Between the Ages of Three and Seven

Anna Harts – Australian National University: Female supremacy: populations benefit from selection of local female optima

Megan Head – Australian National University: Parental Care Evolves in Response to Costs of Mating for Females not Paternity Assurance for Males

Mandy Henningham – University of Sydney: Cut it out: The ethical implications and mismanagement of surgical intervention in infancy on intersexed individuals

Camilla Hinde – University of Wageningen: Individual variation in reproductive strategy and partner negotiation in the great tit

Lin-Chi Hsu – University of Washington: The Timing of Welfare Payments and Domestic Violence

Peter Jonason – University of Western Sydney: When the going gets tough, the Dark Triad predicts selfishness

Debra Judge – University of Western Australia: Child fostering: Using child growth to assess who benefits and who loses when children move across households in rural Timor-Leste

Michael Kasumovic – University of New South Wales: For the love of violent video games: Gender differences in video game preferences, reactions and the potential for conflict

Elias Khalil – Monash University: The Industrial Organization of Patriarchy and Feminism

Rose Khattar – University of New South Wales: The Cultural Legacy of Too Many Men: Traditional Gender Attitudes as the Peacock’s Tail

Sonia Kleindorfer – Flinders University: Female wrens teach their embryos and male partners a family password

Mizuki Komura – Nagoya University: Pension and the family

Sean Leaver – RMIT University:Intergenerational discounting and parental investment in education: Evolutionary basis for a zero discount rate heuristic

Linda MacKay – The Family Systems Institute/University of Notre Dame Sydney: Two competing forces – the need for autonomy and the need for intimacy – how to think about functioning under stress in families and at work

Shiko Maruyama – University of Technology Sydney: Do Siblings Free-Ride in “Being There” for Parents?

Astghik Mavisakalyan – Curtin University: Gender in language and gender in employment

Frank Mazzone – University of New South Wales” A Minor Threat: Parental Investment and Adolescent Anti-Social Behaviour

James Middleton – University of Western Sydney: The masculine undercurrents in the Dark Triad traits

Masahito Morita – The Graduate University for Advanced Studies (SOKENDAI), Japan: Does sexual conflict between parents lead to fertility decline? A questionnaire survey in Japan

Cristina Moya – London School of Hygiene and Tropical Medicine: Inter-generational conflicts over reproductive decisions: A cross-cultural examination of parental presence effects on age at first birth

Alistair Munro – National Graduate Institute for Policy Studies, Tokyo: The lion’s share. An experimental analysis of polygamy in Northern Nigeria

Shinichi Nakagawa – University of Otago: Conflict and cooperation over multiple mating in a bird species with a complex mating system

Lionel Page – Queensland University of Technology: Gender differences in sequential judgement and decisions in mate choice

Gretchen Perry – University of Missouri: Maternal kin take on the care of children in more challenging circumstances than paternal kin

Michael Price – Stanford University: An Ethnographic Test of a Novel Time-Discounting Model of Human Life-History Decisions

Yana Roshchina – Higher School of Economics, Moscow: What determine fertility in modern Russia?

Susan Schaffnit – London School of Hygiene and Tropical Medicine: Modifiers of kin effects on women’s fertility in the UK

Kristin Snopkowski – London School of Hygiene and Tropical Medicine: Intergenerational Conflict: Does ethnic-group postnuptial residence predict age at menopause?

Linda Welling – University of Victoria, Canada: Transferable utility and (in)efficiency in intertemporal bargaining in marriage: interaction of divorce laws and prenuptial agreements

John Weymark – Vanderbilt University: Inclusive Fitness Maximization: An Axiomatic Approach

Stephen Whyte – Queensland University of Technology: Selection Criteria in the Search for a Sperm Donor: Internal Versus External Attributes

Xin Jesse Zheng – University of Sydney: Gender Difference, Fertility Choice and Household Wealth

Anna Zhu – University of New South Wales: Spending longer out of the workforce – does it matter for mothers with young children?

Brendan Zietsch – University of Queenlsand: No trade-off at the genetic level between offspring quantity and reproductive quality in Swedish twins

ABSTRACTS


Stuart Birks – Massey University
Unanticipated consequences of changed relationship legislation (Paper)

Relationships are formed, operate and are dissolved “in the shadow of the law”. There have been major changes in family law over the past forty years, with both Australia and New Zealand going down a similar path to other western countries.

This paper outlines the changes in relationship property legislation drawing on the New Zealand experience. It considers how, from an economics perspective, these are likely to change behaviour and the nature of society.

Risks and returns from relationships have changed, with potential transfer of assets being greater and occurring with more and shorter relationships. This can affect relationship formation and dissolution, as well as behaviour and bargaining positions within relationships. Only a limited range of possible implications were considered in the New Zealand parliamentary debates leading to the legislative changes. This was largely due to narrow framing of the issues. Additional possibilities can readily be predicted using basic economics reasoning. These relate not just to relationships and families, but also to decisions on education, career and lifestyle.

Broader perspectives can also be taken. There are contradictions between aspects of family law, the policy objective of inclusion, concerns about population aging (including issues of care of the elderly), and aspects of happiness research.

While policy changes may be generated through political movements, informal adaptations to the changed environment will also occur. These will result in both anticipated and unanticipated consequences. Consideration of these raises additional questions. Standard economic analysis based on theory and within a tightly specified set of assumptions gives some insights, but it is important to also remember Keynes’ warning about additional reserves, qualifications and adjustments that are necessary for real world application. The paper attempts to present a broad perspective.”

Russell Bonduriansky – University of New South Wales
Can sexual conflict theory shed light on the modern marketplace?

Why are so many consumer products bad for us, and why do we buy them? Within economics, most discussions of marketer-consumer interactions have emphasized mutually-beneficial outcomes, such as industrial innovation, improved product quality, and fulfilment of consumers’ needs and desires. While the potential for negative consequences is also acknowledged, it is typically attributed to externalities or constraints on the efficient functioning of the market. From the biological perspective, maladaptive human behaviours have typically been ascribed to rapid change in environments and lifestyles. I will make the case that a better understanding of modern marketing strategies and consumer behaviour can be gleaned from evolutionary biology and, in particular, the theory of sexually antagonistic signaller-receiver coevolution. Evolutionary theory suggests that signallers and receivers (such as males and females) often experience a conflict of interest that selects for strategies of mutual exploitation and resistance — and the average individual is typically worse off as a result. I argue that an analogous conflict of interest operates within the technologically-sophisticated marketplace of modern human society, driving the development of exploitative strategies that cause net harm to individuals and society as a whole. Although this conflict is a key emergent property of modern market economies, it does not seem to have been recognized in the economics literature. Its recognition may shed light on some baffling aspects of the modern marketplace, and suggest strategies to mitigate its most harmful consequences.

Jenny Brown – The Family Systems Institute & University of New South Wales
Good Cop / Bad Cop: the parenting soft hard split as an adaptation

The family therapy field has long recognised a common pattern of a soft /hard split that develops in response to parenting a symptom bearing child. One parent adapts to the anxiety about the child with increased nurturing and the other shifts to a complimentary position of increased discipline and limit setting. This reciprocity appears to happen automatically in many families and gradually intensifies as each instinctively reacts to the other’s interaction with their child.

This paper will present examples of parent’s reports of this from a qualitative research study on parent’s experience of their adolescent’s mental health treatment. In this particular qualitative sample it is interesting to note that there is not a set gender pattern of mothers appearing soft and fathers firm, rather this binary is expressed evenly amongst gender. Themes emerging from parent interviews include the common tension between parents (including step parents and sometimes other relatives if a father is absent) about the style of parenting that the symptom bearer requires to address their behaviours. The adolescent is an active part of this triangle in being most aligned with the softer parent and antagonistic or distant with the stricter parent. Bowen family systems theory, which is grounded in evolutionary theory, will be used to hypothesise about this phenomenon in families and the costs and benefits that it provides for a family that is anxiously protecting the younger generation. Dr Murray Bowen developed a theory of human functioning out of his years of research and reading from biology and in particular Charles Darwin. He viewed patterns as driven by the shared emotional/autonomic nervous system of other living things. This paper will consider the implications of such a natural systems approach to understanding family tension around parenting and the implications for the functioning of the child.

Andrea Camperio Ciani – University of Padova (with Elena Pellizzari)
Sexually antagonistic selection explains male homosexuality evolutionary conundrum

A variety of social, developmental, biological and genetic factors influence sexual orientation in males. Thus, we tested several evolutionary models to explain the sustenance of genetic factors that influence male homosexuality, despite decreased fecundity within the homosexuals, which has posed a long lasting conundrum in evolutionary studies. Kin selection, the existence of maternal effects and two forms of balancing selection, sexually antagonistic selection and over-dominance, have been analysed as compensatory mechanisms for reduced homosexual fecundity. Here, we suggest that the empirical support for kin selection and maternal effects cannot account for the prerequisites of low universal frequency and stability over time of the distribution of homosexuals. To identify the responsible compensatory mechanism, we analyzed fecundity in 700 mothers and 2,100 European female relatives, i.e., aunts and grandmothers, of either homosexual or heterosexual probands who were matched in terms of age, culture and sampling strategy. The other female relatives were chosen to avoid the sampling bias of the fraternal birth order effect, which occurs when indirectly sampling mothers though their homosexual sons. We observed first that mother of homosexual sons were significantly more fecund that mothers of just heterosexual ones and that also the maternal aunts and grandmothers of homosexual probands were significantly more fecund compared with the maternal aunts and maternal grandmothers of the heterosexual probands. This was true even if these females were not directly mothers of homosexual sons. No difference in fecundity was observed in the paternal female lines (grandmothers or aunts) from either of the two proband groups. Moreover, due to the selective increase in maternal female fecundity, the total female fecundity was significantly higher in homosexual than heterosexual probands, thus compensating for the reduced fecundity of homosexuals. Altogether, these data will be discussed in support an X-linked multi-locus sexually antagonistic hypothesis rather than an autosomal multi-locus overdominance hypothesis to explain this long lasting evolutionary conundrum.

Murshed Chowdhury – King’s University College at Western University
Remitting Behavior of Indian and Chinese Immigrants: Evidence from Canadian Micro-data (Slides)

Immigrants’ remittances to their home countries have been playing an increasingly important role in shaping the global economy. Chinese and Indian immigrants are the two largest groups of Canada bound migration. According to the World Bank, in 2010, China and India are the two highest remittance recipient countries in the world. Using the recently available 3 waves of Longitudinal Survey of Immigrants in Canada (LSIC), this paper investigates the relationships between socio-economic characteristics and remittance behavior of Indian and Chinese immigrants in Canada. To estimate remittance behavior, the study hypothesizes that two broad categories, i.e., individual characteristics, and financial ability to remit are the major factors that influence the possibility to remit. After conducting a logistic regression on the likelihood of remitting and an instrumental variable regression of the amount remitted, the study observes significant differences between remittance behavior of Chinese and Indian immigrants. While Chinese remittances are mostly affected by age, income, level of education and personal investment in home country, Indian remittances are influenced by marital status, having family members in the host country and being involved with social/religious organization in the host country. Financial variables play significant roles for both types of immigrants. These results may assist policy makers from home and host countries in formulating more effective immigration policies. To our knowledge, this investigation, using a panel dataset for Canada, is first of its kind.

Martin Daly – University of Missouri
Discrimination against stepchildren: why so variable?

Discrimination against stepchildren is widespread, but highly variable in its magnitude, both from place to place and across its various manifestations, which range from subtle differences in parental investment to lethal assaults.

The topic is emotionally fraught, and misguided efforts to dismiss “Cinderella effects” as either non-existent or artifactual have been relentless. In response, researchers have focused on repeated demonstrations of the phenomenon’s reality in different populations and in different domains of action, while paying little attention to the task of explaining differences in its magnitude.

Where differential treatment of children is normative, it is relatively easy to justify discrimination against a stepchild, and such discrimination is therefore likely to be more prevalent; such norms vary across societies and across domains of action. Within a society, different factors are likely to be relevant to chronic discrimination versus episodic outbursts. Between societies, differences in norms, institutions, and government policies create differences in the pseudo-parental obligations placed upon stepparents, and may thereby affect the statistical incidence of resentment and hostility.

To begin to address these possibilities, I will present comparisons, both cross-national and across discriminative actions, of the magnitude of Cinderella effects in violence against children and in positive investments in children.

Henry Dixson – The Australian National University (with Jason Low and Benjamin Kenward)
The Ontogeny of Third Party Punishment

Humans cooperate on an unprecedented large scale, and this cannot be accounted for by kin selection (Hamilton 1964) or reciprocal altruism (Trivers 1971) alone. Without punishment of cheaters, cooperation and group cohesion unravels (Fehr & Gachter 2002). The social policing of so-called “free-riders” is therefore an important mechanism in enforcing cooperative norms and sustaining collective action. This can come in the form of 2nd party punishment (punish someone who harmed you directly) and 3rd party punishment (punish someone who harmed someone else). The latter is unique to humans. Although behavioural and cross-cultural research involving adults is well-established, the development of punitive sentiments in children remains relatively understudied. When 3rd party punishment emerges in ontogeny, and to what degree this is culturally modulated, remains an open question. I will present findings from comparative research measuring punishment and altruism among children aged 3-10 years from two socioculturally different climates: the middle-class of Australia’s capital, Canberra, and the Melanesian island nation of Vanuatu. I use Boehm’s (1999) distinction between a free-rider as an economic cheat, and a free-rider as a social bully, to determine how age and cultural background predict children’s willingness to punish these two forms of defector. A further distinction is made regarding the costs of punishment: one is the economic cost in which the child must pay a valued resource to punish, and the other, the social cost of their behaviour being made public. This research project is the first to quantify 3rd party punishment in both a developmental and cross-cultural context. The results provide new insights into the ontogeny of prosocial behaviour and punishment.

Barnaby Dixson – University of New South Wales (with Doug P. Vanderlaan and Paul L. Vasey)
Social support from androphilic kin predicts augmented preferences for masculine mates among Samoan women

The female relatives of same-sex attracted (androphilic) males exhibit elevated offspring production compared those with no same-sex attracted male relatives. In Samoa, androphilic men are referred to as fa’afafine, which means “in the manner of a women”. Fa’afafine exhibit elevated avuncular (i.e., uncle-like) tendencies and behavior toward their nieces and nephews, compared to opposite-sex attracted men and women. We hypothesized that such differences in familial support lead to differences in preferences for masculine traits between heterosexual women with fa’afafine siblings and those without. Although masculine traits signal aspects of biological quality, research indicates that such men have lower romantic attachment and engage in more short-term and extra-pair relationships. Thus, while women who select masculine men as mates may be more likely to produce offspring of potentially higher quality, they are also less likely to receive paternal investment. We tested the hypothesis that the sisters of fa’afafine show stronger preferences for masculine traits than women without fa’afafine brothers by administering questionnaires quantifying preferences for facial hair. We found that both groups had overall stronger preferences for less masculine traits (i.e. clean-shaven faces). However, consistent with our prediction, females with same-sex attracted brothers rated fully bearded faces as more attractive than did females with no same-sex attracted brothers. Our findings provide the first evidence from a non-Western, non-student sample that high social support leads to augmented preferences for masculinity in a potential partner.

Jasper Duineveld – University of Western Sydney
The implicit and explicit motives of the Dark Triad

Research on the Dark Triad (i.e., psychopathy, narcissism, and Machiavellianism) has failed to address the implicit motives behind the Dark Triad behaviour. Insight on the implicit motives of people high on the Dark Triad helps explain their behaviour in new ways. In this study (N = 308) we correlated the Dark Triad with the three main motives (i.e., achievement, power, and affiliation) and their hope and fear components, measured with the Multi-Motive Grid. People high on psychopathy and narcissism were both found to have a high Hope for Success and a low Fear of Loss of Control, showing how people high on these traits may rise to power. Additionally, narcissists also showed a low Fear of Rejection, explaining the high confidence they are known for. People high on Machiavellianism showed little Hope for Affiliation and a high Fear of Rejection. This showed that Machiavellian individuals may manipulate people because they don’t think they can form genuine relationships. Hope for Success and Fear of Loss of Control mediated sex differences in psychopathy and narcissism. The theoretical implications of these findings are discussed in an evolutionary paradigm. This includes the adaptive value of individuals high on the Dark Triad, and how the implicit motives they correlate with support their mating strategies.

Will Feeney – Australian National University
Correlated Evolution of Brood Parasitism and Cooperative Breeding in Birds

The global distribution of cooperatively breeding birds is highly uneven, with hotspots in Australasia and sub-Saharan Africa. Ecological drivers of this distribution remain enigmatic, yet could yield insights into the evolution and persistence of cooperative breeding. We report that the global distributions of obligate brood parasites and cooperatively breeding passerines are tightly correlated, and that the uneven phylogenetic distribution of cooperative breeding is associated with the uneven targeting of hosts by brood parasites. In one facultative cooperatively breeding species this correlation arises because cooperative groups provide superior care to brood parasite young, and because helpers provide defences against fitness loss to brood parasites. Reciprocally selected interactions between brood parasites and cooperative breeders are therefore likely to explain the close association between these two breeding systems.

Hayley Fisher – University of Sydney (with Hamish Low)
The economic consequences of relationship breakdown: income shocks and the extended family

When a marriage breaks down, there are unavoidable financial consequences: losing the economies of scale of cohabitation means it is not possible to maintain living standards for all household members. A substantial body of work has shown that in developed economies, the financial burden falls most heavily on women, who experience large falls in equivalised household income. In contrast, household income often increases for men.

In this paper, we use data from the British Household Panel Survey to examine what explains this phenomenon. We show that women do experience a greater fall in household income on divorce, and that this fall is most pronounced amongst higher income households. Men do not experience a fall in equivalised household income, and those separating from lower income households experience increasing household resources. However, this superior outcome for men is not all it seems: one important means by which men’s household income remains high is their living arrangements. Men are far more likely than women to live with their extended family or other adults, and the additional income of other adults explains a large portion of the difference between men’s and women’s experiences. Once this additional income has been discounted, men also experience a substantial decrease in resources.

These results demonstrate the ongoing importance of extended family networks in smoothing the financial impact of divorce, and suggest that in order to understand these consequences we must examine to what extent these separated individuals share in the resources of the wider household. Moreover these additional support mechanisms alter the outside options for individuals when they are married, and so are likely to affect bargaining power within relationships and so the distribution of resources within traditional households.

Gigi Foster – University of New South Wales and Paul Frijters – University of Queensland
An Economic Model of Power, Gender, and the Value of Singlehood

In this paper, we show how three societal power structures implicitly support competing valuations of being single as opposed to being married. The first structure we consider is that of the male-dominated society, in which coalitions of partnered men and women both face incentives to stigmatize singlehood. For the brotherhood of married men, single men are disruptive and single women are desirable. For the sisterhood of married women in such a society, single men can either be disruptive or an opportunity, but single women are competitors as they reduce the price of sexual services. This combination gives rise to a generalized social stigma on being unmarried, both for males and females. The second power structure we consider adds in a utilitarian state that wields tax-and-spend power. In a society with such a state, the quality signal of being partnered is a useful device for generating tax revenue which is then spent on the lower-utility individuals, i.e., the single people. Finally, we consider the case in which society is transitioning from male-dominated relationships to female-dominated relationships. In such a society, singlehood can be a preferred state while relative wages are changing and social norms about male domination are gradually adjusting. We use our model to generate predictions in regard to expected patterns in fertility, societal attitudes, and the observed prevalence of singlehood, and provide cross-country empirical evidence consistent with these predictions.

Julián Garcia – Max Planck Institute for Evolutionary Biology (with Martin Nowak, David Rand and Matthijs van Veelen)
Evolution of cooperation: reciprocity and population structure

In explaining cooperation biologists and economists have emphasized different mechanisms. Game theoretical models in evolutionary biology and ecology tend to focus on population structure; including models of kin and group selection. Economists, on the other hand, have emphasized the role of reciprocity and direct benefits arising from repeated interactions. Here I present a model that synthetizes these two approaches, and formally inspects the synergies that arise when repetition and population structure act in tandem. We study evolution of strategies for repeated games in an open-ended and rich strategy set that allows for assorted interactions. We are able to predict the evolution of cooperation as a function of assortment (or relatedness) and continuation probability (or discount rate). The parameter space is divided in 5 regions that correspond to different levels of cooperation. Two well-known theories in biology and economics turn out to be specific limit cases in our model: when considering assortment alone, we recover Hamilton’s rule; when looking at repetition alone, we obtain results in line with the Folk theorem. Only when the two ingredients act together, we are able to explain the behavior typically observed among humans; i.e., equilibria with high levels of cooperation, prevalence of conditional strategies and considerable between-individual variation.

Amany Gouda-Vossos – University of New South Wales (with Rob Brooks)
Sex-Differences in Social Cues that Modify Perceived Status

Wage gaps between the sexes are still persistent, even in societies where women have made the largest gains in workplace representation. Economic studies have shown that the wage gap can impact the dynamics within a heterosexual relationship, for example, a woman whose potential income exceeds that of her male partner is more likely pull out of the labour force and subsequently earn less. These conflicts have been shaped by judgements we make about attractiveness and status. A large body of work considers how cues such as facial looks, body mass, and voice pitch influence these judgments however, far less is known about how the social company an individual is seen with can alter these judgments. We asked subjects in online surveys to rate models (male or female) for attractiveness or to estimate their earning capacity as a measure of status. Each model was seen in one of three experimental contexts: partnered with one same sex “friend”; one opposite-sex “partner” or “alone”. Male attractiveness was enhanced by the presence of a female “partner”, a phenomenon known as “mate choice copying”. The most attractive men were not necessarily rated as high-earners as participants estimated the earnings of male targets with male “friends” as the highest, echoing documented links between wealth and collaboration among men. In contrast, female models presented “alone” were rated as the highest earners; the presence of a male downgraded female status as perceived earnings were rated significantly the lowest for females with “partners”. The findings suggest the presence of strong sex-dependent expectations of earning and social influences of attractiveness. I interpret these findings in the context of both evolutionary sexual conflict theory and economic theory concerning mating, couple formation and the importance of resources.

Simon Griffith – Macquarie University
Conflict and cooperation in socially monogamous birds

Most of what we understand about evolutionary conflicts and cooperative behavior in socially monogamous animals has come from the study of relatively few species of short-lived bird that have very predictable and short breeding seasons. These have been studied intensively over many decades in a number of classic ongoing nest box breeding populations in Europe and North America. However, the unpredictability and aridity of the Australian climate presents some fundamentally different challenges for monogamous pairs. Here I will characterize the key elements of the Australian climate and how it is likely to affect reproductive ecology, life history, pair bond behavior and fidelity, and the challenge of coordinating reproductive physiology by males and females. I will present data from our ongoing study of several species of Australian birds, indicating that cooperation at different levels is particularly prevalent on this continent. As well as relatively high levels of cooperative breeding in birds (where many individuals help to raise offspring produced by others), cooperation and coordination appear to be more widespread even within socially monogamous species exhibiting bi-parental care. As well as indicating why the study of socially monogamous birds offer great opportunities to understand the evolutionary dynamics of our own mating system, I will identify predictions to be tested from the contrast of Australian species with those in the northern hemisphere, and the insight they provide into the broad scale environmental influences on the evolution of cooperation and conflict.

Dana Hanna – Australian National University
The Family Constellation, Home Learning Activities and the Progress of Cognitive Ability Between the Ages of Three and Seven

There is a wide and varied literature on the trade off between family quality and aspects of the family constellation, most notably family size. However, little work has been done on the relationship between the progress in quality and the family constellation. To this end, we use data from the Millennium Cohort Study to investigate the effects of the family constellation and home learning activities on the progress of children’s cognitive ability between the ages of three and seven.

We find limited evidence that family size has a statistical or sizable relationship with the progress of children’s cognitive ability. Rather, children of higher birth order and those raised by single parents show, on average, smaller rates of progress between the ages of three and five, and again between the ages of five and seven. Quartile analysis of the data supports this finding and shows that solo-parenting has the greatest effect on those children with higher levels of initial ability.

Parental involvement in all aspects of home learning activities is found to positively contribute to a higher average rate of progress between the ages of three and five and again between five and seven. In particular, the quartile analysis suggests that reading to a child is most beneficial to progress for the younger children, and particularly those children achieving in either the very bottom or the very top quartiles. Help with reading homework, on the other hand, is beneficial for progress to age seven for all but the highest achieving children.

These results suggest that family resource constraints play a smaller role in the progress that children make overall and that parental involvement with home learning activities can positively impact on the progress children make, particularly for those children with a lower level of initial ability.

Anna Harts – Australian National University (with Lisa Schwanz and Hanna Kokko)
Female supremacy: populations benefit from selection of local female optima

Local adaptation and dispersal are both essential for population persistence. Dispersal, however, may also reduce local adaptation because it can introduce alleles that are detrimental in a particular environment. Additionally, selection may favour different optima in males and females, leading to sexual conflict.

Here we show how local adaptation and dispersal co-evolve in two environments with spatial variation in the optimal traits, as well as (potential) local differences between the optimal trait values when expressed by different sexes. In some cases this means that alleles introduced via dispersal may be beneficial for one sex and detrimental to the other.

We focus on a crucial sexual asymmetry. Although gene flow operates via males and females in an equally strong fashion, females are the demographically dominant sex. Hence when the local optimum is more beneficial for the viability of males than females, the population is less productive than when the local optimum is more beneficial for females. As a result, populations with the former local optimum contribute less to the global population gene pool than populations with the latter optimum. Thus in a spatially varying environment, we can predict selection to shift towards female-beneficial trait values, compared with a totally unresolved sexual conflict scenario.

Megan Head – Australian National University (with Camilla Hinde, Allen Moore and Nick Royle)
Parental Care Evolves in Response to Costs of Mating for Females not Paternity Assurance for Males

An understanding of what drives variation in male parental care has proved elusive despite decades of research on this topic. Theory predicts that because females often mate with multiple males and parental care is costly that males should provide more parental care when offspring are more likely to be their own. Empirical evidence in support of this relationship is, however, equivocal. Recently research has highlighted that this lack of support may occur due to a failure to account for co-evolutionary feedback resulting from social interactions between males and females. Mating and parenting are inextricably linked and thus sexual selection could drive the evolution of parental care. We use artificial selection on repeated mating rate (a paternity assurance trait) and mating crosses between and within selection lines to demonstrate how mating behaviour co-evolves with parental care. We found no evidence for co-evolution between male parentage and male parental care. Instead, our results show that variation in patterns of parental care is driven by conflict between the sexes over mating. Females from lines selected for high mating rates provide less care for offspring. Further, our results provide evidence that in bi-parental species where females provide the majority of care selection on females, not males, is the primary determinant of parental care patterns.

Mandy Henningham – University of Sydney (with Gomathi Sitharthan, Elizabeth Riley and Milton Diamond)
Cut it out: The ethical implications and mismanagement of surgical intervention in infancy on intersexed individuals

Western society currently operates under a two sex binary – male and female. So what happens when a child is born and neither sex can be clearly identified? The surgical sex assignment on infants with intersex variations born with ambiguous genitalia is an out-dated practice that still continues today. This cosmetic surgery is done for almost exclusively social reasons to craft a “normal” boy or girl at an age where the individual cannot yet express their gender identity (Diamond & May, 2005). The assumption of being gender neutral at birth has been debunked since the David Reimer case of 1997, so the continuation of this practice has to be questioned. A review of contemporary literature reveals that these surgical interventions on intersexed infants are resulting in an array of mental health, and quality of life concerns later in life. Intersexed individuals often grow up identifying with a different gender to the sex they were surgically assigned, often with the truth of their sex assignments or intersex variations kept hidden from them by health professionals and even parents, under the recommendations of physicians to avoid “shame” (Lev, 2006). In addition to depression, anxiety and isolation, intersexed individuals are also subject to sexual dissatisfaction and even dysfunction as a result of the thousands of nerves severed from surgical interventions (Köhler et al., 2012). Forcing a sex assignment also creates social issues, subjecting them to potential discrimination, creating difficulties in obtaining identification documentation and access to some health services. It is clear that a multidisciplinary approach is needed in order to achieve more effective management of intersexed individuals, including a counselling approach. Further research is required on long term psychological effects is needed in order to create a halt on these practices.

Camilla Hinde – University of Wageningen
Individual variation in reproductive strategy and partner negotiation in the great tit

Individual variation within populations is the driving force behind selection, but has largely been ignored in the search for population-wide selection. In biparental care, individual variation in reproductive strategy has important consequences for cooperation and conflict. Nesting birds are ideal for studying reproductive strategies because investment decisions in eggs and chick provisioning, and responsiveness to partner work rate can be easily quantified. Here I show that, not only do individual female great tits (Parus major) vary in their reproductive strategy, but that such strategies are revealed in their plumage.

A four-year cross-fostering experiment showed that, in some years, females with small plumage stripes invested more in egg laying and less in brood provisioning while the reverse was true for females with large stripes. In other years these relationships were reversed. Females with large or small plumage stripes, and therefore different dominance and aggression levels appear to be making different decisions over pre and post hatching investment between years. Individual optimisation according to the fluctuating resources available may therefore be maintaining this striking variation in strategy and phenotype between individuals. Variation in reproductive strategy has implications for partner compatibility and responsiveness. Partners varied their responsiveness to changes in work rate by partners with different plumage ornaments. How parents respond to, and protect themselves from manipulation by, partners with varying strategies will be discussed.

Lin-Chi Hsu – University of Washington (personal website and paper)
The Timing of Welfare Payments and Domestic Violence

I examine transfer schedules for the Temporary Assistance for Needy Families (TANF) program and find a causal relationship between the time directly after monthly payment and reports of intimidation against women by their intimate partners. This study supports the hypothesis that the husband uses violence or the threat of violence as an instrument to gain control over the allocation of household resources. I also find that states who pay TANF recipients twice a month do not have this effect, suggesting that smaller, more frequent payments can reduce the husband’s incentives to use terror as a bargaining tool.

Peter Jonason – University of Western Sydney
When the going gets tough, the Dark Triad predicts selfishness

Life History Theory researchers have identified the Dark Triad traits – psychopathy, Machiavellianism, and narcissism – as potential adaptations for pursuing a selfish approach to life. In an online experiment of college students (N = 232), we investigated the links between the Dark Triad and individual differences in selfishness/altruism in general and in an understudied context, the family. We randomly assigned participants to imagine they won either AU$1,000 or AU$100,000 in the lottery and asked them to allocate that money to themselves, a favorite sibling, or a favorite cousin. The link between the latent Dark Triad and selfishness was localized to the smaller lottery condition for self and sibling. We would contend this is because the latent Dark Triad is activated under (financial) constraints leading to selfishness; no constraints, no activation of the Dark Triad, no link between the Dark Triad and individual differences in selfishness/altruism. Narcissism was linked to selfishness within the family but psychopathy was linked to selfishness in general and individual differences in narcissism partially mediated sex differences in selfishness. We discuss these findings from the perspective of Life History Theory.

Debra Judge – University of Western Australia (with Linc H. Schmitt, Pyone Myat Thu and Kathy A. Sanders)
Child fostering: Using child growth to assess who benefits and who loses when children move across households in rural Timor-Leste

Parental investment theory purports that parents invest in individual children pursuant to maximized parental fitness. It is not necessarily expected that children will be treated equally. In two research sites in Timor-Leste with economies largely characterized by subsistence agriculture, approximately 20% of over 500 children followed for 2-5 years live in a household without either biological parent. Movements reflect more permanent changes (adoptions) and more fluid residence (fostering). The benefits of fostering may accrue to the trans-locating child (when he/she experiences net improved conditions), to children remaining in the natal household (when competition for food is reduced), or to children in the target household (if the labor dividends provided by the incoming child exceed consumption). If children in biological child only households benefit most, then fostering relationships are a secondary risk aversion strategy. However, fosterage requires the agreement of the adults of two family units that may be more or less related. We use child growth relative to international standards as a measure of the fitness outcomes of fostering. By assessing age structuring of fosterage, net movements relative to amenities and household structure, and the growth of children in three types of households (fostering out only, fostering in, and biological only) we investigate the relative importance of competition and cooperation in fostering practices. Children in a fostering household (both biological and fostered) show better growth than children residing in a household consisting only of biological children. Fostered-in children tend to be older than biological children suggesting that they may provide labor or child care to the fostering household. Although older children show a larger deficit in growth for age, this is equally true for fostered children and biological children. We suggest the cooperative distribution of children relative to a range of resources within broad kinship groups.

Michael Kasumovic – University of New South Wales (with Tom Denson, Barnaby Dixson and Eddie Harmon-Jones)
For the love of violent video games: Gender differences in video game preferences, reactions and the potential for conflict

Since their first introduction to a mass-consumer market in the mid-80’s, video games have become the highest grossing form of entertainment in history. Along with this change in popularity is a change in the demographics of players; what began as a young male dominated interest is now a past time that is equally appreciated by both sexes of all ages. There still, however, exists an average difference in the game preferences of either sex: females prefer word and puzzle games, while males prefer violent, action games. Left- and right- brained theories fall short of explaining these differences since they largely ignore the variance in the distribution of game preferences of either sex. We use a more evolutionary approach to try and explain the variance around sex-specific differences in game preferences. Here I discuss how individual biological responses to violent and non-violent video games affect subsequent abilities to recognize emotional changes and potentially threatening conspecifics, and how this may translate to fitness benefits. I further discuss the potential for conflict between the sexes in virtual spaces and why such conflict occurs.

Elias Khalil – Monash University
The Industrial Organization of Patriarchy and Feminism

Patriarchy and feminism are ideologies that offer distinctly opposite descriptions and policies concerning the division of labor between the sexes. Despite their contrary views, the actual institutions run under either ideology are different in minor details. The deeper structural similarity of patriarchy- as opposed to feminist-inspired institutions highlights that, throughout history, we have at hand basically the same solution to a universal problem: Namely, what is the optimum division of labor concerning procreation? The answer is basically a quid pro quo between the sexes. Males basically express the commitment to a single woman or a defined set of women, in terms of supporting them to have children and bringing up such children. Women, on their part, express the commitment to uphold the project or life goal of the male. One such project is clearly expressed in the almost universal patriarchal lineage system.

Under feminism, this quid pro quo is expressed differently simply as a result of a change in the budget set of males and females as a result of the sexual revolution and the invention of the pill. In traditional, clearly-patriarchal institutions, women maintained the quid pro quo through the monopolistic supply of sex. This means that honor killing, e.g., is mainly a reinforcement of the optimal quid pro quo. In modern, feminist-informed institutions, women have lost monopoly power over the supply of sex. Instead, we witness the rise of the novel and romantic love as a substitute. Either monopoly over sex or romantic love ensures the stability of the equilibrium solution, i.e., the unversal quid pro quo.

This paper provides a model that shows the conditions that explain why the evident quid pro quo is universal. The universal quid pro quo tries to solve the same problem: how to reconcile the different reproductive strategies of males and females.

Rose Khattar – University of New South Wales (with Pauline Grosjean)
The Cultural Legacy of Too Many Men: Traditional Gender Attitudes as the Peacock’s Tail

We document the long-run negative implications of missing women. We exploit a natural historical experiment, which sent large numbers of male and much fewer female convicts to Australia in the 18th and 19th century. In areas with higher gender imbalance, women married more, had more children, and were driven out of high-rank occupations, historically. Today, people have more traditional attitudes towards women working and women are less likely to have high-ranking occupations. The underlying mechanism is that cultural norms, like the peacock’s tail, can serve reproductive fitness but may harm overall fitness, especially in the long run. Historical gender imbalance is associated with an aggregate welfare loss of $800 per year, per person. Our results are robust to a wide array of controls, state fixed effects, and to instrumenting the overall sex ratio by the sex ratio among convicts.

Sonia Kleindorfer – Flinders University (with Diane Colombelli-Negrel and Jeremy Robertson)
Female wrens teach their embryos and male partners a family password

The Superb Fairy-wren (Malurus cyaneus) is an endemic bird in Australia notorious for high levels of male infidelity but shared parental care. In 2012, we made the discovery that female fairy-wrens teach their embryos a password while the embryo is developing in the egg. Females call to their eggs. After hatching, the embryo produces a learned female password as its single element begging call. If the chick produces the correct begging call, it is fed. If it does not, it is abandoned to starve. We swapped clutches of eggs between nests and in all cases the chicks learned the call from the foster mother, and produced a different call compared to its genetic mother. Using in-nest video, pair males only fed chicks that produced the learned begging call. We recorded females sharing the password with the male 10 m surrounding the nest. Females in this system actively teach their embryos and male partners a family password. We discuss the role of female cultural lineages for rates of evolution and manipulation of parental care when male reproductive fidelity is low.

Mizuki Komura – Nagoya University (with Hikaru Ogawa)
Pension and the family

The effects of pension policies on fertility have been examined in the overlapping generations (OLG) model of unitary household in which no heterogeneity between wife and husband exists. This paper departs from the OLG model and focuses on the marital bargaining arising from the heterogeneity in a couple in a non-unitary model. Specifically, this paper examines how the pension policy affects the endogenous fertility of a bargaining couple who have different lifespans. The analysis finds out a new channel of pension policy on fertility decisions: an increase in pension size affects fertility not only via the changes in current and future income, but through a change in marital bargaining power. This channel leads a plausible argument that an increase in a pay-as-you-go (PAYG) pension further accelerates a decline in fertility through the empowerment of women.

Sean Leaver – RMIT University
Intergenerational discounting and parental investment in education: Evolutionary basis for a zero discount rate heuristic

This paper discusses the absence of intertemporal discounting in human parent decision making behaviour associated with choices and investments in their children’s education. This behaviour is inconsistent with standard rational choice theory where parents should maximise the present value of the utility of their consumption choices over time. Nor is it consistent with behavioural economics’ expectation that individuals discount consumption choices across time periods hyperbolically. Parents applying a zero discount rate to the expected future returns from investments in their children’s education is however consistent with evolutionary theory. We propose that the proximate cause of this behaviour is a meta-heuristic, intergenerational temporal empathy, which is constructed from a core set of cognitive biases and heuristics so as to cancel out hyperbolic discounting behaviour normally associated with non-offspring investment related consumption across time periods. The ultimate cause of this meta-heuristic is to eliminate the propensity of hyperbolic discounting behaviour to under-invest in offspring development, thereby ensuring that inclusive fitness is maximised. Intergenerational temporal empathy also has characteristics of a positive feedback mechanism ensuring that beneficial educational strategies are propagated forward and may help explain divergent outcomes for low socio-economic groups where poor educational investment decisions tend to be reinforced across generations.

Linda MacKay – The Family Systems Institute/University of Notre Dame Sydney
Two competing forces – the need for autonomy and the need for intimacy – how to think about functioning under stress in families and at work

Natural systems theory (Bowen, 1978) provides a framework for understanding how people function under stress in families, work communities and wider systems. Two life forces, or evolutionary biological imperatives compete with each other: the need for intimacy and cooperation on the one hand and the need for separateness and autonomy on the other. These two evolutionary biological imperatives tend to be more autonomic than thoughtful, yet they organise functioning across human and non-human populations in powerful and adaptive ways that can both enhance and reduce the capacity for best functioning of the individual or group. However the ability to observe and manage self in one’s family or at work, or in any other social setting by paying attention to automatic behaviour separates humans from other forms of life. This ability – and challenge – can bring about more thoughtful adaptations to stress and change, enhancing leadership as well as whole of system well-being. This presentation will examine these adaptations under stress and focus on the work of operating with the most emotional maturity one can muster in changing and complex times and environments.

Shiko Maruyama – University of Technology Sydney (with Meliyanni Johar)
Do Siblings Free-Ride in “Being There” for Parents?

When siblings are concerned for the well-being of their elderly parents, the costs of caregiving and long-term commitment create a free-rider problem. If siblings living near their parents can share the costs, this positive externality exacerbates the under-provision of proximate living. Location decisions allow siblings to make a commitment to not provide long-term support for parents, and if decisions are made in birth order, elder siblings may enjoy the first-mover advantage. To quantify these effects, we study siblingsÂ’location decisions relative to parents by estimating a sequential participation game that features rich heterogeneity. We find moderate altruism and cooperation in the US that imply: (1) limited strategic behavior: more than 90% of children have a dominant strategy; and (2) non-negligible free-riding: of the families with multiple children, had siblings fully internalized externality and jointly maximized their utility, 18.3% more parents would have had at least one child nearby.

Astghik Mavisakalyan – Curtin University
Gender in language and gender in employment

Women lag behind men in many domains. Feminists have proposed that sex-based grammatical gender systems in languages reinforce traditional conceptions of gender roles, which in turn contribute to disadvantaging women. This article evaluates the empirical plausibility of this claim in the context of the labour market outcomes of women. Based on a sample of over 100 countries, the analysis shows that places where the majority language is gender-intensive have lower participation rates of women in the labour force. Individual level estimates further underscore this finding and indicate a higher prevalence of gender-discriminatory attitudes among speakers of gender-intensive languages.

Frank Mazzone – University of New South Wales
A Minor Threat: Parental Investment and Adolescent Anti-Social Behaviour

Adolescents’ propensity towards anti-social behaviour is influenced by the interaction they share with their peers. Parents make investments into their children that are instrumental in forming pro-social behaviours. However an adolescent’s peer interactions mean that parents’ investment is contingent on the investment made by their children’s peers’ parents. This thesis models the interactions between parental and peer influences in the context of anti-social behaviour. A framework is developed then extended to incorporate wealth heterogeneity and adolescent heterogeneity.

The basic model highlights the problem of parents free-riding off the spillovers of other parents’ investment, leading to underinvestment relative to an efficient first best level of investment. When wealth heterogeneity is incorporated, parents’ incentive to invest any positive amount is conditional on the degree of wealth inequality. When wealth inequality is such that low wealth parents drop out of investment, a large gap grows between the investment that the children of high and low wealth parents receive. Mixing or segregating of parents of low and high wealth is then considered. Although high types have more to gain from being segregated, mixing, when wealth inequality is not too extreme, always provides a higher overall social welfare then segregating. Finally, heterogeneity of adolescents is incorporated. Adolescents now have some individual innate propensity towards anti-social behaviour. This framework is used to illustrate that multiple equilibria exist. Specifically there is an equilibrium in which all parents invest zero. This model also demonstrates that conditions in the environment can be such that there is no incentive for a positive level of investment. Possible solutions to both problems are discussed.

James Middleton – University of Western Sydney (with Peter K. Jonason)
The masculine undercurrents in the Dark Triad traits

The Dark Triad traits (i.e., narcissism, psychopathy, and Machiavellianism) have been examined in relation to a number of interpersonal correlates like mating, social influence, and future-discounting. However, little has been done to examine the proximal psychological factors that might underlie these. In this study (N = 319), we envisioned the Dark Triad traits as a prototypically masculine way of dealing with the world and others. Indeed, prior research in Western and Eastern samples reveal men score higher than women do. We correlate the Dark Triad traits with an array of self-report measures of masculinity along with an indicator of prenatal testosterone during fetal development (the 2D:4D ratio). Beyond exploring these general links, we test whether between- and within-sex variability in scores on the Dark Triad traits can be accounted for by a latent masculinity index. The results of these analyses, and their implications, are discussed from an evolutionary perspective.

Masahito Morita – The Graduate University for Advanced Studies (SOKENDAI), Japan (with Hisashi Ohtsuki and Mariko Hiraiwa-Hasegawa)
Does sexual conflict between parents lead to fertility decline? A questionnaire survey in Japan

In general, theories of behavioral ecology predict that the ideal number of children for women is smaller than for men, because of sex differences in the cost of reproduction and parental care (reviewed in Borgerhoff Mulder & Rauch, 2009, Evol. Anthropol.). We hypothesized that if the modernization of society caused women to have more power in reproductive decision-making, fertility decline should occur (cf. Borgerhoff Mulder, 2009, Am. J. Hum. Biol.). In this study, our two predictions were: (1) the ideal number of children for women should be smaller than that for men and (2) women have more power nowadays in reproductive decision-making than men. To our knowledge, there have been few studies with evolutionary perspectives on the link between sexual conflict of parents and fertility decline in modern developed and low fertility societies.

We conducted a questionnaire survey to mothers at a social facility for childcare in an urban area of Japan in 2012 and 2013. Contrary to our prediction, the ideal number of children for women was not smaller than that for men (12 mothers desired less children than fathers, 74 desired the same and 24 more, when they had no children). Also, we did not find clear evidence that women had priority in reproductive decision-making in their families. In many cases, mothers and fathers were equally positive for and they had equal priority in having children. However, our survey included some limitations. For example, the participants were mainly mothers so we could not get data directly from fathers. We discuss with perspectives of sexual conflict and mating system whether there are no conflict on the number of children between two sexes.

Cristina Moya – London School of Hygiene and Tropical Medicine (with Rebecca Sear, M. Borgerhoff Mulder, H. Colleran, E. Costa, M. Gervais, M. Gibson, A. Goodman, M. Gurven, J. Henrich, P. Hooper, H. Kaplan, M. Kline, J. Koster, I. Koupil, K. Kramer, D. Leonetti, S. Mattison, B. Scelza, M. Shenk, K. Snopkowski, J. Stieglitz, C. von Rueden, J. Ziker, S. Bowles)
Inter-generational conflicts over reproductive decisions: A cross-cultural examination of parental presence effects on age at first birth

Several theoretical models suggest the importance of intergenerational conflicts of interest in allocating household resources, including alloparenting. Parents may improve their children’s reproductive success by reducing grandchild mortality, but they may reduce it by delaying their children’s onset of reproduction. While the former has been documented cross-culturally, the latter has only been shown robustly in post-demographic transition settings. Using data from over 15 societies – the majority of which are small-scale, pre-industrial, and natural fertility – we test the effects of parental presence on women and men’s reproduction. We find that parental presence delays age at first birth for daughters, while fathers are more likely to expedite son’s first births. There is significant cross-cultural variation in this regard; parents delay first births most in post-industrial contexts and least in agricultural contexts. Furthermore, parental delays are smaller in ambilocal societies than in matri- or patrilocal ones. These patterns are consistent with at least two pathways of parental influence on age at first birth: 1) the older generation may win conflicts over limited household labour and resources that can be used towards reproduction and 2) parents may encourage children to invest in embodied capital at the expense of early reproduction, especially in societies where these are more important.

Alistair Munro – National Graduate Institute for Policy Studies, Tokyo (with Bereket Kebede, Marcela Tarazona-Gomez and Arjan Verschoor)
The lion’s share. An experimental analysis of polygamy in Northern Nigeria

In recent years, a small number of researchers have applied the methods of experimental economics to the understanding of cooperation and conflict within the household. Using samples of polygamous and non-polygamous households from villages in rural areas south of Kano, Northern Nigeria we run an experiment to test basic theories of household behaviour. Husbands and wives play two variants of a voluntary contributions game in which endowments are private knowledge, but contributions are public. In one variant, the common pool is split equally. In the other treatment the husband allocates the pool (and wives are forewarned of this). Most partners keep back at least half of their endowment from the common pool, but we find no evidence that polygynous households are less efficient than their monogamous counterparts. We also reject a strong form of Bergstrom’s model of polygyny in which all wives receive an equal allocation. In our case, senior wives often receive more from their husbands, no matter what their contribution. Thus the return to contributions is higher for senior wives compared to their junior counterparts. When they control the allocation, polygynous men receive a higher payoff than their monogamous counterparts. We speculate on the implications of this pattern of investment and reward for the sustainability of polygynous institutions.

Shinichi Nakagawa – University of Otago
Conflict and cooperation over multiple mating in a bird species with a complex mating system

Conflict over mating is a battlefield both within sexes and between sexes because mating opportunities and constrains are directly related to fitness. Extra-
marital or extra-pair mating is clearly beneficial for males, but its benefits for females are still far from clear, especially for species with strong pair-bonds. We studied extra-pair and ‘extra-group’ matings in dunnocks (Prunella modularis), a bird species with the most complex mating system known to date. Although dunnocks possess all the possible mating patterns, most individuals belong to either monogamous or polyandrous groups (at least in our New Zealand population). We show that multiple mating via belonging to polyandrous group and/or engaging in extra-pair mating is beneficial for females. This is because multiple mating reduces the cost of inbreeding. More interestingly and rather surprisingly, males benefit from being in polyandrous groups, because a previous work showed fitness of polyandrous males was severely compromised due to shared paternity. We show that polyandrous males suffer less from extra-group paternity loss due to their coalition on mate guarding. Consequently, each polyandrous male on average produce a similar number of (if not more) offspring to monogamous males that suffer more extra-pair paternity. Furthermore, polyandrous males are often highly related (e.g. brother-brother pairs) and therefore, polyandrous males even gain indirect fitness benefits. Such kin-based polyandry has never been reported in this species in its original range (note that dunnocks were introduced to New Zealand 150 years ago). These observations indicate that the costs and benefits of multiple mating could change drastically over an ecological timeframe when species’ demography or environments are altered.

Lionel Page – Queensland University of Technology
Gender differences in sequential judgement and decisions in mate choice

We use data from the Fisman et al. speed (QJE 2006) dating experiment to study differences in sequential judgements and decisions on mates between males and females. The speed dating experiment provides observations in a controlled environment about mate choice made in a sequential manner, similar to an ecological situation. Participants have to rate and make a choice for each partner sequentially. Participants do not have the possibility to change their judgement and choice made for previous partners.

Evolutionary theory predicts that given the differences in mating strategies between males and females, optimal strategies in sequential choice should differ. We find that males are significantly influenced by the characteristics of the previous partner encountered when making a judgement and choice about a current partner. The more attractive was the previous female partner, the less likely is a male likely to propose a date to the new partner. On the contrary, females do not seem to be influenced by previous partners’ attributes when evaluating a current partner as a possible date.

We discuss the implications of this result and the different characteristics which impact differently sequential mate choices between males and females.

Gretchen Perry – University of Missouri (with Martin Daly)
Maternal kin take on the care of children in more challenging circumstances than paternal kin

This study of kin placements by a Canadian child protection agency investigated which types of kin children are placed with, and what challenges the caretakers faced. We compared the placements with respect to their degree of relatedness, whether they were maternal or paternal kin, and their income, employment, education, physical and mental health, and placement stability. In broad comparisons between kin caregivers and stranger foster parents, kin had greater placement stability and more challenging circumstances in their lives. Among kin caregivers, not surprisingly, close kin, particularly grandparents, and maternal relatives were significantly more likely to be caregivers. Kin caregivers with relatedness ≥ 0.25 made up 88% of all kin caregivers. Maternal grandparents constituted 67% of all grandparents, 70% of all maternal caregivers, and 86% of the grandparents lacking the support of a partner. Overall, maternal kin providing care had less education and employment than paternal kin, and tended to have lower incomes. Maternal kin also provided care with the most extreme physical health diagnoses and seemed to be providing care under the most difficult of circumstances of all kin types, while providing the highest proportion of placements. Maternal kin thus tolerate higher costs to provide care, but their placement stability was the same as with paternal kin.

Michael Price – Stanford University
An Ethnographic Test of a Novel Time-Discounting Model of Human Life-History Decisions

Preferences are central to economics, yet economists are generally agnostic about the ultimate source of preferences. Nevertheless, in recent decades a range of scholars have explored the proposition that contemporary preferences are, at least in part, the product of past and present evolution, which implies that evolutionary models may be useful in predicting contemporary preferences. Despite substantial theoretical work, however, nobody has attempted a serious empirical test of a model which derives preferences from evolutionary parameters. Therefore, for my dissertation field work in eastern Indonesia, which I am currently conducting, I am testing a novel model I have created which derives time discounting preferences from evolutionary parameters (mortality and fertility rates) under the assumption that the inter-temporal marginal rate of substitution of consumption at constant utility is equal to the inter-temporal marginal rate of substitution of consumption at constant reproductive fitness. The model predicts that individuals with different achieved reproductive outcomes (i.e., number and age of children and grandchildren) will possess different time discount rates. To test this prediction I am collecting two types of data: demographic data and subsistence data. From the demographic data I predict households’ time discount rates (the average of the male and female heads of household) using my model, and from the subsistence data I infer actual discount rates using a modified version of the Euler method under the assumption that households which allocate a greater proportion of labor to immediate return subsistence activities (as opposed to delayed return subsistence activities) reveal a relative preference for immediate rather than delayed access to goods. If my model is correct, the slope of the line fitting the observed discount rates to the predicted discount rates will be 1. I report the latest results of my data collection.

Yana Roshchina – Higher School of Economics, Moscow (with Sergey Roshchin)
What determine fertility in modern Russia?

The main purpose of this research is to analyze fertility as a form of economic behavior of households. Russia has been experiencing a great depopulation within 1991-1999, in the large degree due to the fertility decrease. This fact cause serious problems on Russia labor market and have negative influence on economic situation in general. That is why the problem of finding factors influencing fertility is very important for modern Russia. In our previous research we found some factors influencing the fertility in Russia in 1994-2000. But the situation changed in 2000-2012: some measures of demographic policy were adopted, income increased, economic and political systems became more stable. Fertility rate increased too. That is why it is important to compare the determinants of decision about childbearing in two period of new Russian history.

Economic models of fertile behavior are the theoretical background of this research. They were developed in the framework of “new economic theory of family” approach (G. Becker). For empirical models estimates we use RLMS data (Russian Longitudinal Monitoring Survey) for 2000-2012. These models are estimated for following dependent variables: probability of childbearing and the desire to have a child in future. Many economic variables influence family decision-making on a childbearing, however nevertheless major factors which determine reproductive behavior, remain demographic (age and quantity of children ever born) and cultural. Values and cultural factors remain more influencing propensity to parenthood, than economic. The importance of nationality, religiousness, satisfaction by financial position, and also frequencies of alcohol consuming is high. Distinctions between regions are essential, between cities and countryside too. Birth rate is higher in poorer regions, with lower level of female unemployment. Many economic factors which theoretically should influence decision-making on a birth of a child (employment, profession, education, incomes of women and their spouses, conditions of life), appeared insignificant or significant only in models for some samples of women.

Susan Schaffnit – London School of Hygiene and Tropical Medicine (with Rebecca Sear)
Modifiers of kin effects on women’s fertility in the UK

In low-fertility settings, recent research demonstrates that kin affect women’s birth timings and progressions, similarly to natural fertility settings, despite low and non-optimal fertility rates. We use Millennium Cohort Study data from the UK to test the hypothesis that women’s fertility desires may interact with kin measures in affecting women’s fertility such that kin help women achieve their fertility desires. We measure kin presence by women’s parents’ survival status and, additionally, test how specific kin investments (financial support and childcare provisioning) affect the outcome controlling for parental survival. Women entered the data set at the birth of their first child and as such we used event history analysis to analyze second birth timings. Contrary to our hypothesis, we find that maternal grandmother presence relates to accelerated birth progressions for women who do not want children, while having no statistically significant effect on women who do want children. The specific investments of maternal kin have no statistically significant effect on the outcome and in fact, there is some evidence that financial support from parents may actually relate to slower birth progressions. Our results allow for a discussion or how kin may affect women’s fertility, whether through practical help, pro-natal cues or simply through shared genes or shared environments.

Kristin Snopkowski – London School of Hygiene and Tropical Medicine (with Cristina Moya and Rebecca Sear)
Intergenerational Conflict: Does ethnic-group postnuptial residence predict age at menopause?

Human menopause remains an evolutionary puzzle as early termination of fertility does not seem adaptive. Cant and Johnstone (2008) proposed that intergenerational conflict in populations with female-biased dispersal can lead to the termination of fertility in females. One testable prediction from the intergenerational conflict model is that women should experience menopause earlier in groups with an evolutionary history of female-biased dispersal compared to groups with a history of male-biased dispersal. Using data from the Indonesia Family Life Survey on 2400 women aged 40-62 from 16 ethnic groups, we conducted a random effects discrete-time event history analysis of the progression to menopause by ethnic group postnuptial residence. We find no evidence that ethnic groups with a history of patrilocal residence have earlier age at menopause. In contrast, ethnic groups with a history of ambilocal residence have the slowest progression to menopause, while matrilocal and patrilocal ethnic groups have similar progression rates. These findings do not support the intergenerational conflict model and we discuss reasons why we may not expect genetically evolved solutions to intergenerational conflict.

Linda Welling – University of Victoria, Canada (with Elisabeth Gugl)
Transferable Utility and (in)efficiency in intertemporal bargaining in marriage: interaction of divorce laws and prenuptial agreements

In dynamic family bargaining models it is often assumed that spouses have identical and constant marginal rates of intertemporal substitution. A number of authors have recognized that bargaining with commitment may not be an appropriate modelling technique, since spouses’ plans at the beginning of marriage may be subject to renegotiation later on. It has been argued that as long as spouses are at an interior solution, renegotiation does not hinder efficiency. We show that identical and constant marginal rates of intertemporal substitution (ie, transferable utility across periods) is the source of this efficiency result. Even at an interior solution, renegotiation can cause inefficiency if marginal rates of intertemporal substitution are not constant. Our model is the first to pin down this source of inefficiency in a bargaining model in which the threatpoints of later periods are determined endogenously.

For clarity of exposition, we focus on a two-period model. We rule out borrowing or saving, so the family budget constraint binds in each period. We derive the outcomes with commitment, and when the couple recognizes the possibility of renegotiation, and show the interaction of the rules for division of income upon divorce and marginal rates of intertemporal substitution. Given this, we show when this interaction can provide an incentive for prenuptial agreements. We provide both a general framework, and a series of examples.

John Weymark – Vanderbilt University (with Samir Okasha and Walter Bossert)
Inclusive Fitness Maximization: An Axiomatic Approach

Kin selection theorists argue that evolution in social contexts will lead organisms to behave as if maximizing their inclusive, as opposed to personal, fitness. Inclusive fitness is central to much work on the evolution of social behaviour. It has been used to understand diverse biological phenomena, including sex-ratios, co-operative breeding, dispersal, reproductive skew, group formation, and more. The inclusive fitness concept allows biologists to treat organisms as akin to rational agents seeking to maximize a utility function. We develop this idea and place it on a firm footing by employing a standard decision-theoretic methodology. We show how the principle of inclusive fitness maximization and a related principle of quasi-inclusive fitness maximization can be derived from axioms on an individual’s ‘as if preferences’ (binary choices). Our results help integrate evolutionary theory and rational choice theory, help draw out the behavioural implications of inclusive fitness maximization, and point to a possible way in which evolution could lead organisms to implement it.

Stephen Whyte – Queensland University of Technology
Selection Criteria in the Search for a Sperm Donor: Internal Versus External Attributes

Despite extensive literature on female mate choice, empirical evidence on women’s preferences in the search for a sperm donor is scarce, even though this search, by isolating a male’s genetic impact on offspring from other factors like paternal investment, offers a naturally ‘controlled’ research setting. In this paper, we work to fill this void by examining the rapidly growing online sperm donor market, which is raising new challenges by offering women novel ways to seek out donor sperm. We not only identify individual factors that influence women’s preferences but find strong support for the proposition that inner values are more important in these choices than exterior values. We also find evidence that physical factors matter more than resources or other external cues of material success, perhaps because the relevance of good character in donor selection is part of a female psychological adaptation throughout evolutionary history. The lack of evidence on a preference for material resources, on the other hand, may indicate the ability of socialisation and better access to resources to rapidly shape the female decision process. Overall, the paper makes useful contributions to both the literature on human behaviour and that on decision-making in extreme and highly important situations.

Xin Jesse Zheng – University of Sydney
Gender Difference, Fertility Choice and Household Wealth

This paper formulates a micro-founded and optimization based choice model where husband and wife make inter-temporal fertility decisions to optimize utilities and household’s wealth subjecting to financial and health constraints, specifically, husband and wife make rational and dynamic decisions about the number of children to produce and the expenditure on children to maximize household’s wealth over life span. Gender differences in decision making about fertility choice and wealth accumulation are captured by specifications of utility functions, preference parameters and income constraints. Hypothesis concerning whether husband and wife’s optimal fertility decisions differ in direction and magnitude due to heterogeneous utility functions, household income, inflation and child welfare policies is tested. The methodologies involve random utility discrete choice models governing a couple’s behavior from the theoretic perspective and linear regression estimation with parametric distributions of random coefficients from the empirical perspective. Panel data including Australian birth rates, household income, female/male earnings, maternity leave payment, mortality rate, child-care subsidies, education expenses, living costs indices and household expenditure on health are collected to test the theory empirically. The conclusions are that the optimal number of children and expenditure on children are jointly determined by risk aversion coefficients of utility functions, household income, child care expenses and subsidies.

The choice to produce the first baby is a balanced outcome from the interaction among the dynamics of household income, number of marriages, maternity payment, difference in men and women’s earnings, mortality rate and the number of women who worked after child birth. The choice to produce multiple babies is influenced additionally by decreasing marginal child care cost and congestion cost in raising multiple children. The choice of expenditure on raising children is more flexible and dynamic, couples make a series of optimal choices in accordance with each period’s child-care subsidies, education expenses and living costs indices.

Anna Zhu – University of New South Wales (with Bruce Bradbury)
Spending longer out of the workforce – does it matter for mothers with young children?

This paper examines the impact of school starting age on Australian mothers’ initial and later employment. Any such impacts are particularly relevant to policy decisions about when to commence schooling and whether to subsidise additional child care places for pre-school children. In the unemployment literature, concern is often advanced about hysteresis in employment – unemployment in one period increasing the likelihood of later unemployment. We test for the existence of a similar employment relationship following mothers’ absence from employment before their children start school. Exogenous variations in age at school entry are used to test for the existence of increases in mothers’ employment associated with school entry and any longer-term impacts on employment. The age at entry variations arise from entry cut-off rules which mean that children whose birthdates are one day apart, but lie on either side of the cut-off date, can begin school one year apart. We find that eligibility for school entry has a significant initial impact on mothers’ employment, but this effect quickly disappears. On average, additional time out of the workforce when children are young does not lead to any persistence in non-employment among mothers. Our main results are based on Australian administrative data of around 6,100 partnered mothers receiving family payments between 2001 and 2006.

Brendan Zietsch – University of Queenlsand (with Ralf Kuja-Halkola, Hasse Walum and Karin J. H. Verweij)
No trade-off at the genetic level between offspring quantity and reproductive quality in Swedish twins

Reproductive success is widely used as a measure of fitness. However, offspring quantity may not reflect genetic contribution to subsequent generations if there is non-random variation in offspring quality. Offspring quality is likely to be an important component of human fitness, and trade-offs between offspring quantity and quality have been reported. As such, studies using offspring quantity as a proxy for fitness may yield erroneous projections of evolutionary change, for example if there is little or no genetic variance in number of grandoffspring or if its genetic variance is to some extent independent of genetic variance in number of offspring. To address this, we performed biometrical modelling using data on the reproductive history of all 16,268 Swedish twins born 1915-29 and their offspring. There was significant sex-limitation in the sources of familial variation, but the magnitudes of the genetic and environmental effects were the same in males and females. We found significant genetic variation in number of grandoffspring (16% of the total variation), but it could be completely accounted for by the genetic variation in number of offspring – there was a perfect genetic correlation between number of offspring and grandoffspring. Shared environment played a smaller but significant role in number of offspring and grandoffspring; again there was a perfect shared environmental correlation between the two traits. These findings support the use of lifetime reproductive success as a proxy for fitness in populations like the one used here, but we caution against generalising this conclusion to other kinds of human societies.