Unveiling the Effects of Natural Disasters and Nuclear Energy on the Secondary Sex Ratio: A Comprehensive Review

Abstract

The secondary sex ratio (SSR), defined as the ratio of male to female births in a population, has long been a subject of scientific inquiry due to its potential as a health indicator. The interplay between catastrophic events and the delicate balance of male and female births presents a nuanced and compelling study area. Natural disasters, such as earthquakes, hurricanes, floods, and volcanic eruptions, have been known to disrupt ecosystems and human populations, leading to both short-term and long-term consequences. Studies have suggested a potential influence of these disasters on the SSR, with varying degrees of impact observed across different regions and disaster types. Similarly, nuclear accidents, such as the infamous Chernobyl disaster, have sparked interest in their potential effects on human health and development. The release of radioactive materials into the environment can have far-reaching consequences, including impacts on reproductive outcomes. Through a rigorous examination of the existing literature, the present review aims to synthesize current knowledge on the impacts of natural disasters and nuclear accidents on the SSR and unravel the mechanisms that explain SSR fluctuations. By shedding light on the diverse influences shaping the SSR, this narrative review contributes to a deeper appreciation of the intricate interplay between environmental, biological, and societal factors that determines the SSR, calling for targeted strategies to mitigate potential adverse effects on sex ratios in the aftermath of such events.

Keywords: earthquakes; natural disaster; nuclear energy; population dynamics; public health; reproductive health; secondary sex ratio.

Figure 1

The effects of earthquakes on the secondary sex ratio (SSR). Each examined earthquake is denoted by a specific symbol displayed in the uppermost box. The time required to observe a shift in the SSR following each earthquake is depicted. A red bullet indicates a statistically notable SSR decline, while a yellow bullet indicates no significant alteration in the SSR. The studies related to the 2008 Sichuan earthquake and 2001 Gujarat earthquake did not refer to specific times regarding alterations in the SSR; thus, they are depicted separately. The figure was created on BioRender.com.

Figure 2

The effects of nuclear energy on the secondary sex ratio (SSR). Operation of nuclear power plants, atomic bomb tests, and nuclear accidents could lead to an increased SSR through lethal mutations in the germline, especially in paternal X gametes, or through thyroid dysregulation in pregnant women. Although most of the studies revealed SSR declines following the Chernobyl disaster (1), one study showed a possible decline in the SSR due to this incident (2). The figure was created on BioRender.com.