A new study published in Human Nature reports that parents do not simply invest more in daughters or sons overall; rather, their investment differs by domain, with mothers, fathers, daughters, and sons showing distinct patterns.

Human parenting is unusual in the animal kingdom because it is long-lasting, costly, and often involves substantial care from both mothers and fathers. Much of the previous research on parental investment has focused on broad questions, such as how much time or money parents spend on children, rather than examining the many different ways parents invest in offspring.

Yet human parenting includes much more than food, protection, and money. Parents also teach skills, offer emotional support, guide social behavior, shape moral values, encourage education, and provide advice about relationships and adult life.

“I’ve always been really interested in kinship dynamics, such as familial cooperation and conflict, across species,” said Sid Dougan, a doctoral researcher at the University of Texas at Austin and lead author of the study. “Parenting is an aspect of human behavior characterized by the constant tug-of-war between cooperation and conflict, both between mothers and fathers, and between parents and offspring.”

Dougan noted that past research on human parenting has produced mixed results regarding differences in investment between mothers and fathers, and between daughters and sons. “I think is because most studies have been very narrow in scope and have not considered the broad and diverse forms that human parenting takes,” he said. “I wanted to address this by examining a much broader and more detailed range of parental behaviors, and by developing hypotheses that predict and explain differences in parental investment.”

To do so, Dougan and colleagues examined whether these different forms of parental investment vary depending on both the sex of the parent and the sex of the child. Their study was motivated by an evolutionary framework suggesting that parents may invest differently in daughters and sons when those children have historically faced different adaptive challenges.

“Women and men face many of the same adaptive challenges — challenges that directly or indirectly affect survival and reproductive success. But they also face some challenges that fall much more heavily on one sex than the other,” Dougan explained. “Our findings suggest that the ways parents invest in their offspring today are, at least in part, a reflection of the adaptive challenges our ancestors faced over hundreds of thousands of years of evolution. Natural selection has favored psychological mechanisms that motivate parents to invest in offspring in ways that prepare them for the challenges they are likely to face, so we should expect some aspects of parenting to differ between daughters and sons.”

Likewise, Dougan added, “Because mothers and fathers have faced some different adaptive challenges over our evolutionary history, natural selection has favored somewhat different parenting competencies in each, so we should expect some aspects of parenting to differ between mothers and fathers.”

For example, daughters may receive more guidance around relationships and protection, whereas sons may receive more encouragement in athletics, competition, or practical skills. The researchers also expected mothers and fathers to differ in domains where their own experiences or sex-linked roles may have shaped different forms of parental expertise.

The researchers analyzed data from 105 adults, 49.5% of whom were female, who had originally been recruited as part of a longitudinal study of newlywed heterosexual couples. These couples were first recruited in 1989 through public records of marriage licenses issued in Washtenaw County, Michigan, USA. The present analyses used data collected at the second time point, when participants were in their third year of marriage. Participants ranged in age from 19 to 36 years, with an average age of 26. Most identified as white, and most reported being raised in suburban areas of the United States.

Participants completed a 105-item questionnaire about parental behaviors they experienced while growing up. For each item, they rated separately how much the behavior was performed by their biological mother and biological father, using a scale from 0, meaning “not at all,” to 7, meaning “a great deal.” The authors then organized the parental behaviors into conceptually distinct domains.

After removing items that were too vague or overlapped across categories, the final measure included 73 behaviors grouped into 13 domains: mating and relationship guidance, athletics and physical training, mechanical and practical skills, social and moral guidance, competitive encouragement, sexual permissiveness, direct care and domestic support, bonding and emotional support, education and career support, protection, discipline and regulation, wisdom and life guidance, and material provisioning.

Overall, mothers provided more parental investment than fathers when all domains were averaged together, although this difference was especially clear for daughters. Daughters received more investment than sons in mating and relationship guidance, protection, and material provisioning. Sons received more investment than daughters in athletics and physical training, competitive encouragement, and sexual permissiveness. In other words, the findings did not suggest a simple pattern in which one sex received more parental investment overall. Instead, daughters and sons appeared to receive different kinds of investment.

The results also showed differences between mothers and fathers. Mothers invested more than fathers in direct care and domestic support, bonding and emotional support, social and moral guidance, discipline and regulation, mating and relationship guidance, and wisdom and life guidance. Fathers invested more than mothers in athletics and physical training, as well as mechanical and practical skills.

Some domains showed no meaningful sex differences, including education and career support, where mothers and fathers invested similarly and daughters and sons received similar levels of support.

Several interactions also emerged. Mothers showed a stronger daughter-focused pattern in mating and relationship guidance, whereas fathers showed stronger son-focused patterns in athletics and physical training, and mechanical and practical skills.

While many of the patterns aligned with the authors’ hypotheses, a few findings stood out as unexpected.

“One aspect that surprised me was in the domain of competitive encouragement,” Dougan told PsyPost. “Over evolutionary time, compared to females, male reproductive success has depended more on direct contest competition and status. So, I predicted that sons would receive more competitive encouragement than daughters on average. This is exactly what the results showed, but what I did not expect was that it’s not just a father thing: mothers also encourage their sons to be competitive more than they do their daughters.”

“In hindsight, this makes perfect sense,” he added. “Individuals spread their genes not only through their own direct reproduction, but also through ‘inclusive fitness’ — the reproduction of relatives that share copies of their genes. Mothers therefore benefit, just as fathers do, by encouraging competitiveness in their sons because their sons’ reproductive success also contributes to the mothers’ inclusive fitness.”

The authors noted that the sample was relatively small and drawn from a Western, educated, industrialized, rich, and democratic context (WEIRD), which limits how confidently the findings can be generalized across cultures.

“This study used a relatively small sample, and the parental behaviors examined don’t encompass every domain of parental investment,” Dougan acknowledged. “Like any single study, the findings should be interpreted cautiously until they have been replicated in larger samples using even more comprehensive measures of parenting.”

To that end, the research team is already looking ahead to their next project. “The next step is to develop a broader, more detailed parental investment measure that captures as many aspects and domains of parenting as possible, and that applies to parents across cultures, from modern Western populations to small-scale hunter-gatherer societies,” Dougan said. “I’m currently finishing the development of such a measure and very soon will be attempting to replicate and expand on the results of this first study in a much larger sample. A long-term goal is to then apply this parental investment measure cross-culturally and across different family compositions to assess how stable or variable patterns of parental investment are.”

Ultimately, Dougan hopes the findings inspire a shift in how scientists approach the study of family dynamics.

“I see this study as a first step toward developing a more comprehensive understanding of parental investment. I hope it encourages researchers to think about parenting as a diverse set of behaviors that have been shaped by different evolutionary pressures, rather than measuring parenting using only broad measures, such as overall time spent with offspring, or focusing on just one or two domains of parenting,” Dougan said.

He also offered an important clarification regarding how to interpret evolutionary psychology findings. “Evolutionary explanations are often misunderstood as suggesting how people should behave. But that is not what the evolutionary framework, or this research, is about. The goal is simply to understand why certain patterns of parenting exist, not to prescribe how mothers or fathers ought to raise their children.”

The study, “Sex Biases in Patterns of Parental Investment,” was authored by F. Sid Dougan, William Costello, and David M. Buss.