An accidental evolution lab
The Chernobyl Exclusion Zone, established after the 1986 nuclear disaster, is an unintentional laboratory for evolutionary biology. In the immediate aftermath, animal populations crashed. Studies conducted in the years following the event showed that in the most contaminated forests, bird species richness dropped by more than 50%, and total bird abundance fell by 66%. The primary source of this radiation is concentrated in the top layer of soil, affecting birds that consume soil invertebrates most severely.
Decades of chronic, low-dose radiation exposure have exerted immense selective pressure on the birds that remained. Not all species were affected equally. Researchers analyzing 97 bird species found that 64 species experienced population declines correlated with radiation levels. 33 species showed stable or slightly increased populations, possibly due to reduced competition for resources. This divergence created a living experiment, allowing scientists to investigate the specific traits that determine survival in a radioactive environment. Some birds, like barn swallows (Hirundo rustica), have shown elevated mutation rates, higher frequencies of physical abnormalities, and reduced reproductive success in highly radioactive areas. Other observed effects across various species include smaller brain sizes and a high incidence of radiation-induced cataracts.