May 21, 2026 07:41 PM
https://www.eurekalert.org/news-releases/1129213
INTRO: Scientists have reported it for decades: Overpopulation can impair reproduction. Crowded chickens lay fewer eggs. Crowded mice have smaller broods. In humans, several studies have associated increased population density with reduced fertility.
External factors, such as resource scarcity and social influences, undoubtedly play a role. But researchers have long suspected that intrinsic, biological mechanisms may also be at play as an evolutionary tool to keep populations in check.
New University of Colorado Boulder research, published this month in the journal Nature Communications, identifies one key mechanism. It found that overcrowded animals secrete a chemical messenger that can damage eggs, impair embryos and cause genetic mutations in offspring for generations to come.
“It has been well documented that population density has a direct and negative impact on human and animal fertility, but the underlying mechanisms have been elusive,” said senior author Ding Xue, professor of molecular, cellular and developmental biology at CU Boulder. “Our study provides novel insights into how overpopulation can cause various developmental defects, including reduced fertility and increased mortality.”
The study comes as the world population nears 8.3 billion— three times what it was in 1950. Meanwhile, the authors note, birth rates are on the decline. Worldwide, the fertility rate has gone from five births per woman in 1950 to 2.3 births in 2021. According to the World Health Organization, one in six people experience infertility (defined as the inability to achieve a pregnancy after 12 months of trying).
“Overpopulation and crowding stress have emerged as major challenges in contemporary societies, especially in urban cities, where two-thirds of the world population live,” said Xue. “Our study may provide important molecular insights into the underlying health problems that can come with it.” (MORE - no ads)
INTRO: Scientists have reported it for decades: Overpopulation can impair reproduction. Crowded chickens lay fewer eggs. Crowded mice have smaller broods. In humans, several studies have associated increased population density with reduced fertility.
External factors, such as resource scarcity and social influences, undoubtedly play a role. But researchers have long suspected that intrinsic, biological mechanisms may also be at play as an evolutionary tool to keep populations in check.
New University of Colorado Boulder research, published this month in the journal Nature Communications, identifies one key mechanism. It found that overcrowded animals secrete a chemical messenger that can damage eggs, impair embryos and cause genetic mutations in offspring for generations to come.
“It has been well documented that population density has a direct and negative impact on human and animal fertility, but the underlying mechanisms have been elusive,” said senior author Ding Xue, professor of molecular, cellular and developmental biology at CU Boulder. “Our study provides novel insights into how overpopulation can cause various developmental defects, including reduced fertility and increased mortality.”
The study comes as the world population nears 8.3 billion— three times what it was in 1950. Meanwhile, the authors note, birth rates are on the decline. Worldwide, the fertility rate has gone from five births per woman in 1950 to 2.3 births in 2021. According to the World Health Organization, one in six people experience infertility (defined as the inability to achieve a pregnancy after 12 months of trying).
“Overpopulation and crowding stress have emerged as major challenges in contemporary societies, especially in urban cities, where two-thirds of the world population live,” said Xue. “Our study may provide important molecular insights into the underlying health problems that can come with it.” (MORE - no ads)
