A new study has unravelled how overpopulation can impair reproduction. The study, which used crowded mice with smaller broods to arrive at its result, found that such crow could shrink the possibility of fertility, giving credence to several studies that have associated increased population density with reduced fertility in humans.
External factors, such as resource scarcity and social influences are said to also play a role. However, researchers have long suspected that intrinsic, biological mechanisms may also be at play as an evolutionary tool to keep populations in check.
New CU Boulder research, published in the journal, Nature Communications, identifies one key mechanism. The study 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 of the study and professor of Molecular, Cellular and Developmental Biology at CU Boulder, Ding Xue.
“Our study provides novel insights into how overpopulation can cause various developmental defects, including reduced fertility and increased mortality,” Xue added.
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 Organisation, 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.
“Our study may provide important molecular insights into the underlying health problems that can come with it,” Xue said.
The research team stumbled upon the findings serendipitously while studying a phenomenon known as radiation induced bystander effect (RIBE).
