On April 26, 1986, disaster struck near the Ukrainian-Belarusian border when a series of steam explosions led to the meltdown at the Chernobyl Nuclear Power Plant, then part of the Soviet Union. The disaster affected hundreds of thousands of people and left a contaminated landscape that scientists are still trying to understand 40 years later.

But now, something strange is happening. The Chernobyl Exclusion Zone (CEZ), a roughly 1,000-square-mile perimeter around the nuclear plant, is slowly becoming one of the world’s biggest science experiments for exploring the long-term effects of ionizing radiation. While humans might’ve abandoned the area, other animals—including wolves, dogs, frogs, boars, and deer—stuck around.

In 2016, a study found that the Eastern tree frogs (Hyla orientalis) in the CEZ exhibit different characteristics than their neighboring cousins, and in 2023, another study discovered distinct genetic differences between Chernobyl dogs and dogs living only 10 miles away in Chernobyl City. And last month, Princeton University biologists Cara Love and colleagues published a Molecular Ecology paper on radiation-induced stress and possible selection on immune targets in Chernobyl wolves.

Analyzing wolves in the CEZ is particularly interesting because they’re apex predators, a.k.a. the top of the food chain. This is usually a privileged position in an ecosystem, but when that ecosystem is inundated with radiation, these animals are forced to eat irradiated prey that ate irradiated plants that grew out of irradiated soil. Basically, it’s radiation all the way down.

The first surprise is that wolves aren’t scarce in the zone. Love previously told NPR that wolf populations in the CEZ were seven times denser than in protected wildlife areas in neighboring Belarus. But a new Proceedings of the Royal Society B study on mammals in the Ukrainian exclusion zone strengthens a simpler explanation for why large animals are doing so well there: restricted human access.

Abundance and adaptation aren’t the same. There may be a surprising amount of wolves in the CEZ because it gives them room, prey, and a break from hunting pressure and other human disturbance. Their immune systems and genomes may also show signs of living under chronic radiation stress.

“Gray wolves offer a really interesting opportunity to understand the impacts of chronic, low-dose, multigenerational exposure to ionizing radiation,” Princeton scientist Shane Campbell-Stanton said in an NPR interview. “As an evolutionary biologist, the very first question in my mind was whether or not this radiation was enough of a stressor to actually be a selective pressure.”

In 2014, the Princeton team attached collars to these CEZ wolves with both GPS and radiation dosimeters, in an effort to understand the population’s response to Chernobyl’s cancer-causing radiation. They discovered over time that the wolves were consistently exposed to radiation six times higher than the legal limit for humans.

The peer-reviewed paper now supports a narrower version of that idea. Love and colleagues reported altered leukocyte composition, gene-expression patterns consistent with radiation-related immune modulation, and accelerated Chernobyl-specific divergence at loci associated with immunity and response to oncogenesis. That means the wolves appear to carry immune and genetic signals that fit life under chronic radiation stress. But the paper doesn’t necessarily prove that Chernobyl wolves get cancer less often, survive cancer better, or have evolved into cancer-proof animals.

“So in general, we found that the fastest-evolving regions within Chernobyl are in and around genes that we know have some role in cancer immune response or the anti-tumor immune response in mammals,” Campbell-Stanton told NPR. The new paper keeps that possibility alive, but describes “putative selection” on immune targets, not a proven cancer-survival mechanism.

Love’s current project language says the team is studying whether radiation-resilience mechanisms in CEZ populations could someday inform “novel therapeutic or protective strategies” in human medicine. Campbell-Staton’s project page frames the same idea as a question: can daptive evolution inside the CEZ serve as a useful model for human cancer therapeutics?

For decades, Chernobyl has been characterized as an immense ecological disaster (which it definitely was), but in the past decade, the CEZ has also looked more and more like an unprecedented scientific opportunity.