The challenges posed by the COVID-19 pandemic have prompted researchers to explore its possible impact on all aspects of life, including human biology. Peyton Cleaver and Dr. Amy Non of the University of California, San Diego, took an in-depth look at whether the crisis has affected the number of boys born in the United States compared with total births. Their findings, published in the journal Evolutionary Anthropology, shed light on this intriguing subject.
Scientists have long been interested in the Trivers-Willard hypothesis, which suggests that mothers are more likely to give birth to daughters in stressful situations because daughters are thought to have a better chance of surviving hard times. and chances of reproductive success. Researchers used years of national birth records and applied detailed statistical methods to investigate whether the stress caused by the pandemic affected the likelihood of having a boy.
Drs Cleaver and Nong found no significant changes in the proportion of boys born during two key periods: the months after the initial lockdown and later in the year. This ratio, known as the sex ratio at birth, measures the ratio of male births to the total birth rate and is often used as a marker of population health trends. “Our research shows that the pandemic has not caused the expected decline in male birth rates nationwide,” Cleaver explained. Instead, the study revealed significant differences based on factors such as the mother’s race, age and education level, with slightly lower male birth rates for mothers from poorer backgrounds.
Experts note that women with lower levels of education, which often reflects socioeconomic status, as well as black and Hispanic women, are less likely to have boys than white and Asian women. These patterns are consistent with earlier research showing that persistent stressors, such as financial hardship and systemic inequality, may impact pregnancy outcomes. In this context, stressors refer to long-term stressors that may affect health, such as financial insecurity or discrimination. “Although the differences are small, when spread out over millions of births each year, they highlight the profound social and health disparities in our society,” Dr. Nong said.
The study’s findings contrast with international research, which reported temporary declines in the proportion of boys born in countries such as South Africa and Japan during the early stages of the pandemic. These differences may reflect differences in how governments handle the crisis, public perceptions of the threat, and levels of popular stress. In the United States, for example, a fragmented approach to managing the pandemic may have resulted in less intense, widespread stress than in countries with a more unified response.
The researchers also highlighted the challenges of studying changes in the ratio of boys to total births. These changes are influenced by complex biological and environmental factors and are often used to detect population health patterns rather than individual conditions. While their analysis of large amounts of data is robust, Drs. Cleaver and Dr. Nong stress that the changes should be viewed as a sign of broader social trends rather than individual maternal health conditions. They call for further investigation into how social stress, hormonal and environmental factors combine to influence pregnancy outcomes.
Ultimately, this study demonstrates the stability of human reproductive patterns in the early months of the pandemic in the United States. It also serves as a reminder that social conditions play an important role in health outcomes, even during a global crisis.
Journal reference
Cleaver, P., & Non, AL (2024). “During the early months of the COVID-19 pandemic, were fewer boys born in the United States? A test of the Trivers-Willard hypothesis. Evolutionary Anthropology, 33, e22043. DOI: https:// doi.org/10.1002/evan.22043
About the author
Dr. Amy L. Nong 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 and influence health disparities across the lifespan. Dr. Non leads the Epigenetic Anthropology Laboratory, which studies the interplay of genetics, epigenetics, and early social factors in shaping human health. Her work often centers on racial and socioeconomic inequalities, aiming to understand their biological underpinnings and their long-term impact on chronic disease. With a passion for interdisciplinary collaboration, Dr. Non integrates anthropology, biology, and public health into her research to contribute to solutions to pressing health challenges. She is a dedicated mentor who guides the next generation of scientists to address issues of inequality through rigorous research. Recognized for her significant contributions, Dr. Nong’s work bridges evolutionary anthropology and contemporary public health issues, positioning her to play an important role in understanding human adaptability and resilience.
Peyton Cleaver is an emerging scholar in the field of biological anthropology, currently pursuing a bachelor’s degree at the University of California, San Diego. Cleaver has a strong interest in human reproductive biology and health disparities, and his research focuses on how social stressors influence sex ratio at birth and other reproductive outcomes. She is actively engaged in groundbreaking research on the biological impacts of systemic inequalities, including the impact 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 analyzes and work effectively with senior researchers. Her work is informed by a passion for understanding how biology and society intersect, particularly in the context of human development and health equity. Through her scholarship and dedication to advancing knowledge, Cleaver is expected to make a lasting impact in the field of biological anthropology.
