Recent research published in International Journal of Psychology provide evidence that insecure attachment styles tend to be associated with a larger number of children. This research suggests that cultural norms play an important role in how our deeply ingrained relationship habits influence family size. These findings question the assumption that a secure attachment style is always the most beneficial trait for reproductive success.
Attachment theory explains how early interactions with caregivers shape how people relate to others throughout their lives. According to this framework, individuals develop pragmatic models of themselves and others that guide their expectations in romantic partnerships and friendships. These relationship patterns are generally categorized into different styles such as secure, fearful, preoccupied, and neglectful.
People with a secure attachment style tend to have a positive view of themselves and others, which helps them develop strong communication skills. This emotional foundation usually results in stable and satisfying relationships that are suitable for planned family growth. In contrast, insecure attachment styles involve varying degrees of relationship anxiety, emotional avoidance, or an unpredictable combination of the two.
Fear attachment involves negative views of both oneself and others, often leading to fear of rejection and difficulty maintaining partnerships. Preoccupied attachment is characterized by excessive dependence on others for approval, which can result in highly dependent and conflict-prone relationships. Negative attachment styles include emotional detachment and a strong preference for self-sufficiency, often leading people to avoid deep emotional connections.
These relationship patterns not only influence romantic partnerships but also tend to shape parenting behaviors and family planning. “Attachment theory is one of the most influential frameworks in psychology, but its discussions often center on emotional security and relationship quality rather than its generational effects,” says Marian Fisher, professor of psychology and Santa Maria Scientific Research Chair at St. Mary’s University in Halifax. Fisher is also an affiliated faculty member at the Kinsey Institute and co-author of a forthcoming book. Evolutionary Psychology: A Very Short Introduction.
The researchers wanted to see whether patterns of relationships were related to family size in the same way around the world. “We were interested in whether adult attachment styles are related to reproductive success, that is, the number of children a person has, and whether such patterns look the same in different cultural settings,” Fisher explained. “Japan, Canada, and the United States provided us with three contexts with very different family norms and fertility trends. This provided a useful test to see whether attachment operates in a universal way or changes with culture.”
Life history theory provides a useful lens for understanding these complex dynamics. This biological concept suggests that organisms adapt their reproductive strategies based on the stability of their environment. Fast life history strategies involve investing less in individual offspring and producing more offspring.
Rapid strategies can be adaptive responses to unpredictable environments and unstable relationships. On the other hand, a slow strategy has fewer children but invests more time and resources in each child. The scientists suspected that secure attachment might be consistent with a slower reproductive strategy, especially in individualistic countries where autonomy and resource-intensive parenting are common.
To test these ideas, researchers collected data from exactly 15,120 participants through a large-scale online survey. The sample was split evenly between the three countries, with 5,040 respondents from Japan, 5,040 from Canada, and 5,040 from the United States. To ensure balanced representation, we divided the sample equally between men and women within each country.
The researchers also divided the participants evenly into five specific age groups. These groups ranged from people in their 20s to over 60 years old. This equal stratification ensured that scientists had sufficient statistical power to make meaningful comparisons between different generations.
Participants completed a standardized psychological tool used to measure adult attachment styles. The survey presented four short paragraphs, each describing a different relationship style. Participants rated the extent to which each description matched their own attitudes and interpersonal behaviors on a 7-point scale.
To measure reproductive success, the survey asked participants to report the actual number of biological children they had. The researchers also asked participants about their ideal number of children they would like to have. This dual approach allowed the authors to compare actual family size and individual reproductive goals across three different cultures.
Data analysis revealed that in all three countries, people with fearful and preoccupied attachment styles tended to have more children. “Essentially, attachment styles that are typically classified as anxious (i.e., fearful or preoccupied) were associated with having more children, and that pattern held in all three countries,” Fisher told PsyPost. She noted that in Canada and the United States, secure attachment, often treated as the ideal, was associated with fewer children, although this was not the case in Japan.
This negative association in North America suggests that securely connected individuals may prefer behaviors that lead to smaller, more planned family sizes. “This means that attachment styles that we tend to judge as less desirable don’t necessarily have reproductive costs,” Fisher explained.
The association between fear attachment and number of children was actually strongest in Japan. At the same time, secure attachment showed no significant relationship with actual number of children in the Japanese sample. “I have to admit, the differences in Japan are interesting and show how influential cultural norms around family can be,” Fisher said.
“Thus, while secure attachment predicted fewer children in Canada and the United States, this was not the case in Japan. This suggests that culture shapes how attachment affects family life, at least in terms of the number of children someone has,” Fisher said. The authors propose that Japan’s collectivist values, combined with strong economic pressures and a national trend toward delayed child-rearing, may override the influence of individual attachment styles. In such environments, external social factors may play a more dominant role in reproductive decisions than personal relationship habits.
Researchers also observed significant gender differences in attachment styles across different cultures. In Canada and the United States, women scored higher on preoccupied attachment and men scored higher on fearful attachment. These results are consistent with traditional social norms in individualistic societies, where women are encouraged to focus on building relationships and men often strive for emotional independence.
In Japan, the pattern was slightly different, with women scoring higher on preoccupied, secure, and dismissive attachment styles. This complex combination may reflect the contemporary tensions faced by Japanese women as they seek to balance traditional caregiving expectations with increasing pressures to succeed in their professions. Japanese men had the highest fear attachment, emphasizing local cultural expectations of emotional restraint and interpersonal vigilance.
Although the findings of this study provide evidence linking relationship style and family size, readers should put the scope of the results into perspective. “The important thing to keep in mind is that with our sample, even effects this large or small can be statistically detectable, so the reader needs to assess actual significance separately from statistical significance,” Fisher explained. She added that these are general trends studied in thousands of people and are not strong predictors of how many children a particular individual will have.
This study also includes some methodological limitations that provide context for the results. “Because this design is correlational and cross-sectional, it shows relationships rather than causes, and third factors may interact with both attachment style and reproductive success,” Fisher cautioned. This means that it is impossible to say whether a particular attachment style directly causes a person to have more children.
Furthermore, this method relied solely on people reporting their feelings and history. “This data also comes from online self-reporting in three developed countries, so we need to keep that in mind,” Fisher said. The researchers also used a short, four-item questionnaire to measure attachment, which may lack the precision of long-term psychological studies.
In the future, the research team hopes to expand their focus to different types of populations. “We want to think more about the role of culture, especially in terms of the vast differences in parenting across communities,” Fisher said. The study relies on populations in highly industrialized countries, which limits how universally applicable the findings can be.
“Ideally, we would like to rerun the study using a naturally fertile (i.e. not using hormonal contraceptives) sample rather than WEIRD to further investigate the extent of the relationship,” Fisher explained. The acronym WEIRD stands for Western Society, Educated Society, Industrialized Society, and Prosperous Democratic Society. Exploring these dynamics in non-WEIRD populations could help scientists understand exactly how environmental factors interact with relationship habits on a global scale.
The study, “Attachment Bonds and the Baby Boom: A Cross-Cultural Study of Reproductive Success,” was authored by Marianne L. Fisher, T. Joel Wade, Hidenori Komatsu, Nobuyuki Tanaka, Hiromi Kubota, Rebecca Birch, Katherine Salmon, and David Widman.
