About the effects of radiation, Chernobyl was serious:
When a safety system test at one of the Chernobyl power plant’s reactors went badly wrong in April 1986, explosions unleashed a fiery plume of debris and radioactive atoms, or radionuclides, into the air that, over several days, may have emitted several hundred times more radiation than the atomic bomb dropped on Hiroshima. More than two dozen first responders died within months after rapidly absorbing doses of up to 13,400 millisieverts (a sievert is a unit of radiation absorption; normal background radiation levels are usually around 1.5 to 3.5 millisieverts a year.) Over subsequent decades, thousands of children and adolescents who likely absorbed somewhat lower doses developed thyroid cancer, a cancer type that, fortunately, most tend to survive.Katarina Zimmer, “Scientists can’t agree about Chernobyl’s impact on wildlife” at Knowable Magazine (February 7, 2022)
The people left, the wild animals stayed, absorbing low-level radiation. While early reports suggested things were fine, a later one (open access here) documented such effects as a decline in numbers of various species, smaller brains and less viable sperm at higher radiation levels. That report came to be disputed, as Zimmer writes:
But some other research teams have not found significant radiation effects on the genetic diversity or abundance of certain animals around Chernobyl. In one widely publicized 2015 survey of a Belarus area near the power plant, a team of scientists determined that the numbers of elk, roe deer and wild boar were similar to those in radiation-free nature reserves in the region. No matter what the consequences of lingering radiation might be, there were massive benefits to people leaving.Katarina Zimmer, “Scientists can’t agree about Chernobyl’s impact on wildlife” at Knowable Magazine (February 7, 2022)
The fact that there were no longer any humans in the area is bound to be a confounding factor. At any rate, however radiation might affect the wildlife, population sizes did not decrease. Good will in the research community, however, did:
The stubborn discrepancies have caused some members of each camp to become distrustful of the other’s conclusions, and on some occasions the debate has turned personal. In 2015, the International Union for Radioecology, a nonprofit group of radiation scientists, invited researchers from both sides to a meeting in Miami, striving to reach a consensus. But the conversation became so heated, “they started hurling insults at each other,” recalls McMaster University radiobiologist Carmel Mothersill, the IUR’s treasurer. The only conclusion they could reach was that “everything is so uncertain in the low-dose region that you can’t attribute anything definitively to the radiation dose.”Katarina Zimmer, “Scientists can’t agree about Chernobyl’s impact on wildlife” at Knowable Magazine (February 7, 2022)
In science fiction, maybe radiation would result in new mutant species but it didn’t happen when radiation was inadvertently tried on a large scale on the ground.
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Darwinism must have bypassed Chernobyl. In 2011, it was noted that Chernobyl, forbidden to humans due to radiation after the nuclear accident, had not shown signs of new species evolving by natural selection acting on random mutations (Darwinism), as hoped. But it was simply teeming with usual wildlife. (June 24, 2019)
After Chernobyl, Eden? (March 10, 2011) From the source: “Twenty-five years after the Soviet-era meltdown drove 60,000 people from their homes in the Ukraine, a rebirth is taking place inside the exclusion zone. With Geiger counter in hand, the author explores Europe’s strangest wildlife refuge, an enchanted postapocalyptic forest from which entirely new species may soon emerge.” What was mainly new was that the animals showed no fear of humans.