Challenges brought by the COVID-19 pandemic have led researchers to explore its possible effects on various aspects of life, including human biology. Peyton Cleaver and Dr. Amy Non from the University of California San Diego delved into whether the crisis influenced the number of boys born compared to total births in the United States. Their work, published in Evolutionary Anthropology, sheds light on this fascinating topic.
Scientists have long been intrigued by the Trivers–Willard hypothesis, a theory suggesting that under stressful circumstances, mothers are more likely to give birth to daughters because daughters are thought to have a better chance of survival and reproductive success in tough times. Using years of nationwide birth records, the researchers applied detailed statistical methods to investigate whether the stress caused by the pandemic affected the likelihood of giving birth to boys.
Cleaver and Dr. Non found no significant changes in the ratio of boys born during two critical periods: a few months after the initial lockdown and later in the year. The ratio, known as the sex ratio at birth, measures the proportion of male births compared to total births and is often used as a marker for population-level health trends. “Our research shows that the pandemic did not cause the predicted decrease in male births across the country,” Cleaver explained. Instead, the study revealed notable differences based on factors like race, age, and education level of the mothers, with mothers from less advantaged backgrounds showing slightly fewer male births.
Experts noted that women with lower educational attainment, which often reflects socioeconomic status, as well as Black and Hispanic women, were less likely to have boys compared to White and Asian women. These patterns align with earlier studies suggesting that ongoing stressors, such as economic hardships and systemic inequality, can influence pregnancy outcomes. Stressors in this context refer to long-term pressures that can affect health, such as financial insecurity or discrimination. “Although the differences are small, when spread across millions of births each year, they underline the deep social and health disparities in our society,” Dr. Non remarked.
Findings from this research stand in contrast to international studies that reported temporary drops in the ratio of boys born in countries like South Africa and Japan during the pandemic’s early stages. These differences may reflect variations in how governments handled the crisis, public perceptions of the threat, and levels of stress among populations. For example, in the United States, a fragmented approach to managing the pandemic may have resulted in less intense, widespread stress compared to nations with more unified responses.
Researchers also highlighted the challenges of studying shifts in the ratio of boys to total births. These shifts, which are influenced by complex biological and environmental factors, are often used to detect patterns in population health rather than individual conditions. While their analysis of extensive data was robust, Cleaver and Dr. Non emphasized that such changes should be seen as signs of broader societal trends rather than individual maternal health conditions. They called for further investigation into how social stress, hormones, and environmental factors combine to shape pregnancy outcomes.
Ultimately, this study demonstrates the stability of human reproductive patterns during the early months of the pandemic in the United States. It also serves as a reminder of the significant role societal conditions play in health outcomes, even during a global crisis.
Journal Reference
Cleaver, P., & Non, A.L. (2024). “Were fewer boys born in the United States during the early months of the COVID-19 pandemic? A test of the Trivers–Willard hypothesis.” Evolutionary Anthropology, 33, e22043. DOI: https://doi.org/10.1002/evan.22043
About the Authors
Dr. Amy L. Non is a leading biological anthropologist and professor at the University of California, San Diego. Her research focuses on how social and environmental experiences are biologically embedded, influencing health disparities across lifespans. Dr. Non directs the Epigenetic Anthropology Lab, where she investigates the interplay of genetics, epigenetics, and early-life social factors in shaping human health. Her work often centers on racial and socioeconomic inequalities, aiming to understand their biological underpinnings and long-term impacts on chronic diseases. With a passion for interdisciplinary collaboration, Dr. Non integrates anthropology, biology, and public health in her research, contributing to solutions for pressing health challenges. She is a dedicated mentor, guiding the next generation of scientists to address inequities through rigorous research. Recognized for her significant contributions, Dr. Non’s work bridges evolutionary anthropology and contemporary public health issues, making her a prominent voice in understanding human adaptability and resilience.
Peyton Cleaver is an emerging scholar in biological anthropology, currently pursuing her undergraduate studies at the University of California, San Diego. With a keen interest in human reproductive biology and health disparities, Cleaver’s research focuses on how social stressors influence sex ratios at birth and other reproductive outcomes. She has actively contributed to groundbreaking studies on the biological impacts of systemic inequality, including the effects of the COVID-19 pandemic on human birth patterns. As a Triton Research and Experimental Learning Scholar, Cleaver has demonstrated her ability to engage in complex analyses and collaborate effectively with senior researchers. Her work is grounded in a passion for understanding how biology and society intersect, particularly in the context of human development and health equity. With her academic achievements and dedication to advancing knowledge, Cleaver is poised to make a lasting impact in the field of biological anthropology.
