A recent study published in Evolutionary Psychology suggests that a neighborhood’s economic and demographic conditions can predict the reproductive patterns of its residents 15 years later. By analyzing millions of data points from the Canadian census, scientists found that areas with higher rates of poverty and certain minority populations tend to experience different rates of family formation in the future. These findings provide evidence that early environmental factors might shape long-term family planning trends, which could help guide public health policies.
Vinícius Betzel Koehler, a sessional faculty member in the Department of Psychology, Neuroscience & Behaviour at McMaster University, and M.D. Rutherford initiated this research to test an idea known as psychosocial acceleration theory. This concept stems from a broader biological framework called life history theory, which looks at how living things distribute their limited energy. Because humans cannot invest unlimited time and energy into everything, our bodies and minds unconsciously adapt to favor either physical growth or early reproduction depending on our surroundings.
“I have been interested in evolutionary psychology since my M.Sc.,” Koehler said. “Life history theory and psychosocial acceleration theory (PAT) are two big concepts in Evo Psych that are currently going through serious reviews and criticisms.”
He explained that if these ideas hold true, researchers should be able to observe the effects on a large scale. “If their postulates are correct, in lay words, if the human species adapted to start a developmental clock depending on the environment they encounter in their first years of life, we should see indications of it everywhere, including in national censuses,” Koehler said.
“It made sense for me that we should test PAT postulates with entire populations,” Koehler added. “Another major motivation is that it could also be of incredible value for policymakers if we could use such theories and variables to predict populational reproduction tendencies.”
Psychosocial acceleration theory suggests that growing up in harsh and unpredictable environments cues a person to mature faster. Harshness generally refers to conditions with high risks of mortality or a severe lack of resources. Unpredictability refers to sudden life changes, such as a parent leaving the home or lacking a reliable routine. In these difficult settings, the theory proposes that reproducing early and frequently maximizes a person’s chances of passing on their genes before a potential early death.
Past research exploring this theory has mostly relied on small groups of participants or specific surveys. Koehler and Rutherford wanted to see if these patterns hold up across an entire country’s population over a long period. They specifically chose to look at Canada to see how a modern, high-income environment affects reproductive timelines on a massive scale.
To test these ideas, the researchers gathered publicly available data from the 2006 and 2021 Canadian censuses. This 15-year gap allowed them to look at the environments of children in 2006 and observe the reproductive outcomes of young adults in 2021. They examined the data at two different geographic scales to see which provided the most accurate predictions.
The first geographic scale included 39,481 dissemination areas, which are small neighborhoods containing roughly 400 to 700 people. The second scale consisted of 240 census divisions, which are much larger and stable regions made up of neighboring municipalities. The researchers expected the larger regions to provide more reliable data because massive population shifts are less common across large borders.
The scientists extracted specific variables from the 2006 data to represent environmental harshness and unpredictability. For harshness, they looked at median family income, the percentage of homes needing major repairs, and the proportion of households spending more than thirty percent of their income on rent. To measure unpredictability, they tracked unemployment rates, geographic mobility, and the prevalence of single-parent or divorced households.
For their reproductive measures in 2021, the authors looked at the average size of families, the number of children per family, and the average family size of single parents. They used a statistical modeling technique to see how well the 2006 environmental factors predicted the 2021 reproductive outcomes. The scientists evaluated the models based on how much of the variance in future reproductive patterns could be explained by the past data. Variance simply refers to how much the numbers change or spread out across different regions.
As anticipated, the models using the larger census divisions proved to be the most accurate predictors. In these larger divisions, the 2006 data successfully explained eighty-one percent of the variance in frequent reproduction in 2021. The past data also explained sixty-four percent of the variance in the family size of single parents, which is a notably high success rate for a study in psychology.
The specific relationships they uncovered provided a mix of support and contradiction for psychosocial acceleration theory. A higher percentage of children living in low-income households in 2006 predicted a larger number of single-parent households 15 years later. This specific finding aligns with the idea that early financial hardship influences future family structures and cues faster reproduction.
However, other forms of hardship predicted the exact opposite of what the theory expects. Higher unemployment rates and high rental costs in 2006 were negatively associated with both frequent reproduction and single parenting in 2021. In other words, areas with severe employment instability and expensive housing actually saw fewer large families and fewer single parents in the future.
The authors also noted that standard measures of hardship might not capture the unique struggles faced by marginalized groups. In Canada, Indigenous peoples and visible minorities historically experience disproportionate rates of discrimination, systemic inequalities, and trauma. The scientists suspected these specific challenges act as strong environmental cues for accelerated reproduction, prompting them to include these demographic factors in their analysis.
“We also tested if the percentages of visible minorities would be predictors of reproduction patterns,” Koehler told PsyPost. “We hypothesized that they would be predictors because we know that visible minorities, such as Indigenous populations and immigrants, usually face much harsher and unpredictable circumstances than the general population.”
“They ended up being significant predictors, but much less than what I personally expected,” he noted. “I was also surprised to see that in Canada proxies of a harsh life worked contrary to PAT postulates; that is, in places where people seemed to have a harsher life, they seemed to reproduce less often 15 years later. This is also different from the results we found in Brazil.”
To ensure they were observing a timeline of human development rather than just a random statistical association, the researchers ran a reversed model. They tried to use the 2021 data to predict the 2006 outcomes. This reversed timeline failed to produce an acceptable model, which provides evidence that the relationship flows in a specific developmental direction over time.
“The average person could probably assume that the postulates of PAT are correct and try to offer a resourceful and predictable environment to their children,” Koehler said. “I believe the concept of predictability is the biggest one here.”
“In a different study, we have asked participants about their infancy and asked if their parents got home from work at around the same time every day, if there were times that only one of the parents was at home, if meals were also consistently offered and around the same time, if they knew their parents were there to support them, etc. etc.,” Koehler explained.
“It’s the takeaway that being there for their children every day can significantly alter many outcomes throughout their whole lives,” Koehler said. “I think there is no risk for the average person of assuming that PAT theory is correct if we later find out that it isn’t.”
As with all research, there are some caveats to consider. The most significant limitation is the reliance on geographic data rather than tracking individual people. It is entirely possible that the individuals living in a specific neighborhood in 2006 were not the exact same people living there in 2021.
“This research was conducted testing population data,” Koehler explained. “We were testing percentages or averages of census divisions and of dissemination areas. You can understand that as ‘census language’ for a municipality and for a group of around 10 blocks of dwellings.”
Canada has high rates of immigration and internal migration, meaning population shifts could influence the patterns the researchers observed. Because of this geographic focus, the findings might not apply perfectly to individual human behavior. A neighborhood might show a mathematical link between early hardship and larger family sizes, but entirely different groups of people within that neighborhood could be driving those two separate statistics.
“We were also gathering data in one year to try to predict data about the same area 15 years later,” Koehler said. “We don’t know, and we can’t assume that they were the same people. So this is far from being a definitive test of PAT or a claim that people living in the conditions described in the paper will have the reproductive patterns that we found. Nonetheless, the findings should be useful for policymaking and understanding populational reproduction tendencies.”
Additionally, alternative explanations outside of evolutionary theory might explain the results. Factors such as a lack of institutional support, cultural differences, and local social norms heavily influence reproductive choices. In modern societies, access to higher education and health care tends to delay childbirth, which might explain why certain harsh economic conditions actually predicted lower rates of reproduction in this specific study.
Moving forward, Koehler plans to expand this line of research across different populations and formats. “We tried some research with social media data, too,” he said. “Since the theory is going through serious criticisms and reviews, I think it would be useful to collect data from as many sources as possible to see where and how it gets the predictions right and where it fails.”
“If I have the chance, I will continue to do that,” Koehler added. “Testing LHT-P predictions from multiple data sources (census, social media, university student participants, non-university samples, etc.) and from different countries with different levels of development and different cultures.”
The study, “Childhood Demographics and Socioeconomic Conditions Predict Reproduction 15 Years Later,” was authored by Vinícius Betzel Koehler and M.D. Rutherford.
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