More confirmation of the Trivers-Willard hypothesis: Sons from high-status families achieve higher educational outcomes than daughters, while daughters from low-status families surpass sons

Parental background and daughters’ and sons’ educational outcomes – application of the Trivers-Willard hypothesis. Janne Salminen, Hannu Lehti. Journal of Biosocial Science, January 6 2023. https://www.cambridge.org/core/journals/journal-of-biosocial-science/article/parental-background-and-daughters-and-sons-educational-outcomes-application-of-the-triverswillard-hypothesis/47FD4388B618EB5E078336813FEB71E3

Abstract: This study uses Trivers-Willard hypothesis to explain the differences in daughters’ and sons’ educational outcomes by parental background. According to the Trivers-Willard hypothesis (TWH), parental support and investments for sons and daughters display an asymmetrical relationship according to parental status because of the different reproductive advantage of the sexes. It predicts that high-status parents support sons more than daughters, and low-status parents support daughters more than sons. In modern societies, where education is the most important mediator of status, the TW hypothesis predicts that sons from high-status families will achieve higher educational outcomes than daughters. Using cohorts born between 1987 and 1997 from the reliable full population Finnish register data that contain the data of over 600.000 individuals, children’s educational outcomes were measured using data on school dropout rate, academic grade point average (GPA), and general secondary enrollment in their adolescence. OLS and sibling fixed-effect regression that permitted an examination of opposite-sex siblings’ educational outcomes within the same family were applied. Sons with high family income and parental education, compared to daughters of the same family, have lower probability of dropping out of school and are more likely to enroll into academic secondary school track. In families with low parental education or income daughters have lower probability for school dropout and enroll more likely to academic school track related to sons of the same family. The effect of family background by sex can be interpreted to support TWH in dropout and academic school track enrollment but not in GPA.

Discussion

This study investigated whether parental socioeconomic resources influence sons and daughters differently. The biosocial theory – the Trivers-Willard hypothesis – which states that parents with high social status invest more in sons compared to low-status parents who invest more in daughters, was applied. Sibling fixed-effects regression models were utilised by observing how parental education and family income influence sons’ and daughters’ GPA, dropout rates from secondary school and general secondary enrollment with reliable Finnish register data.

The results show that parental education has a stronger positive effect on sons’ educational outcomes than daughters in all three measured outcomes. Family income has an even more pronounced effect for dropping out from secondary education and for general secondary enrollment. However, family income did not influence the GPA based on the siblings’ sex. These results are in line with previous studies that have studied TWH in the United States (Hopcroft, Reference Hopcroft2005; Hopcroft & Martin, Reference Hopcroft and Martin2016; Pink, Schaman, & Fieder, Reference Pink, Schaman and Fieder2017). Additionally, the results support the claim that boys are more sensitive to family’s resources than girls in terms of educational outcomes (Autor et al. Reference Autor, Figlio, Karbownik, Roth and Wasserman2019; Brenøe & Lunberg, Reference Brenøe and Lundberg2018).

The result that found the largest Trivers-Willard effect for general secondary enrollment compared to dropout and GPA indicates that parents may guide children’s educational decision-making process. Thus, parents probably give guidance to their children according to their own human and economic capital; however, this study adds that the guidance can be different for sons and daughters depending on family conditions. The biosocial mechanism explains why family conditions influence differently for sons’ and daughters’ education.

Limitations

Although we can obtain reliable information with register data, there are still some limitations despite large dataset and objective information. We were not able to obtain information about the exact nature of parental behavior for children’s benefit. The lack of direct measure of parental investment is the one limitation and thus it is difficult to observe exact mechanism between parental resources and child’s educational outcome.

However, previous studies show that parental SES and the amount of investment correlates highly (see Tanskanen & Danielsbacka, Reference Tanskanen and Danielsbacka2019). Further, the results show that parental education and family income had the strongest TWH effect on general secondary enrollment compared to dropout and GPA. Thus, it can be stated that the results of the study reflect parental investments in the form of human capital accumulation of the children, because children continue to pursue higher education very likely after general secondary education that leads to higher income and socioeconomic status in adulthood. However, parents may have lower possibilities to influence children’s risks of school dropout. Avoiding school dropout does not necessarily lead to high status in adulthood, but children who avoid dropout and continue secondary schooling avoid low status and income in adulthood. GPA is determined highly by children’s intelligence and other non-cognitive traits that parents find very difficult to influence in Finland due to the absence of private schools. It has been shown, for example, that individuals’ variations in GPA are largely explained by genes but not shared environmental effects such as family background (Nielsen, Reference Nielsen2006). Finnish schools that have very low variance and thus show low inequality of learning outcomes can even amplify the genetic effects and reduce the effects of parents and thus that of TWH on GPA.

This study could not control for health and psychiatric variables. Thus, the results may reflect the fact that boys have more learning difficulties than girls (for example in the case of ADHD and other neurotypical disabilities), particularly among low status families; however, the study controlled for GPA that considers at least some of the effect of learning disabilities.

The findings come from a Finnish birth cohort born in 1987–1997. This cohort has experienced relatively high equality of opportunity in school context and the egalitarian welfare state has supported their families throughout their childhood. For these cohorts, all education levels have been free of charge. The funding of the schools and universities are based on governmental finance. There is no private school at any education level. According to the Global Gender Gap Report (2021), Finnish society is the second most gender-egalitarian country in the world and on average, women are better educated than men. However, previous studies have shown that parental education rather than family income is associated with education and later social status in Nordic countries (Elstad & Bakken, Reference Elstad and Bakken2015; Erola et al., Reference Erola, Jalonen and Lehti2016) Surprisingly, the study still found that higher family income decreases the educational disadvantage for boys. Because this effect was found in the Nordic welfare context it suggests that in other countries with different institutional context that includes tuition fees, the effect of the family income could be even stronger. If TWH is seen as universal it should be influential despite the institutional context. The results support this interpretation because the effect is found also in contexts where parental resources should not matter for children’s education. This indicates that parents’ and children’s evolutionary adaptations that mold their cognitive architecture (biases) and behavior are effective in modern societies. Additionally, the result of family income is surprising because in contemporary western societies experience an abundance of resources that leads to high investment in all children (Hopcroft, Reference Hopcroft2005). It can be argued that the logic of the TWH is problematic because high status males do not have a higher probability to reproduce than high status females on an average in all modern societies due to the use of contraception (Hopcroft, Reference Hopcroft2005). However, this argument has not gained empirical support because previous studies show that still in many modern societies high status men have higher probability to have more children than lower status men (Nisén et al. Reference Nisén, Martikainen, Myrskylä and Silventoinen2018; Nettle & Pollet Reference Nettle and Pollet2008; Weeden et. al. Reference Weeden, Abrams, Green and Sabini2006; Lappegård & Rønsen Reference Lappegård and Rønsen2013; Hopcroft Reference Hopcroft2019). Furthermore, it is important to acknowledge while applying evolutionary explanations that individuals usually do not consciously try to increase their (inclusive) fitness and maximize the number of offspring as standard rational theories used in social science would assume. Instead, it is assumed that humans have cognitive mechanisms that guide them to put effort into things that would have tended to increase (inclusive) fitness during evolutionary history (Hrdy, Reference Hrdy2011). In an evolutionary framework, parental investments are defined as any investment by the parent in a child that increases the child’s likelihood to survive and hence reproductive success at the cost of the parent’s ability to invest in another child (Trivers, Reference Trivers

1972). Thus, parental investments mean parental behavior, for example parental care, that increases a child’s inclusive fitness. Therefore, future research should analyze parental behavior by combining register and survey data to get an even more thorough picture of TWH.