A sign warning of radiation from the explosion at Chernobyl. Photo by Zoriah, used under Creative Commons licensing.Chernobyl's explosion in 1986 was the largest nuclear accident ever. In terms of radiation release, it exceeded Hiroshima by a long shot. And although the hulking ruin continues to threaten today, still hot under its cement and lead cap, nature is reclaiming what was once hers—before humans stripped her forests; before they hunted, plowed, and planted; and before they built four nuclear reactors. In the days following the disaster at Chernobyl, radioactive elements rained down upon towns, forests, and distant landscapes, settling on rooftops, leaves, soil, rivers, and lakes. These unstable elements spewed out high-energy atomic bits that rip apart the molecules of life—killing cells and busting apart strands of DNA. Some will continue discharging these lethal bits for decades; others for centuries. Even in the days before Google, it wasn’t hard to imagine the utter destruction that enveloped the region as radioactive iodine, strontium, cesium, and plutonium settled into lakes and forests and the bones and bodies of those unlucky enough to live within the disaster’s influence. I was a young graduate student at that time, immersed in the world of cancer-causing chemicals that warped, twisted, and snipped apart bits of DNA, and it wasn’t hard for me to imagine the inevitable menagerie of mutant fish, fowl, and furred creatures that would surely haunt the land for decades to come. Within days of the accident, tens of thousands of acres of pine forest—subsequently known as the red forest—died. And yet, amidst the destruction and despite the radioactivity that lingers across the landscape today, the abandoned towns, fields, and forests are not inhabited by populations of twisted mutants. Instead, depending on whom you read, at least some of Nature’s children are thriving. For nearly twenty years, Texas Tech scientists Ronald Chesser and Robert Baker have studied life in the Chernobyl Exclusion Zone. Originally a 30-kilometer radius from the explosion’s ground zero, the zone now covers more than 2000 square kilometers, including some of the most contaminated real estate in the world. The pair recalled visiting the site for the first time, eight years after the blast, writing, “We were completely taken aback by what we saw…” Amidst once-unimaginable destruction was life, and plenty of it. “The ‘Exclusion Zone’ has effectively become a preserve.”
A vole of the genus studied by Ronald Chesser and Robert Baker. Photo by Vitalii Khustochka, used under Creative Commons licensing.But their first observations had been deceiving. Going in, the scientists found just what they had expected. Surveying the local vole population for mutations or signs of mutation, in the form of increased genetic variation, they found plenty. “The mutation rate in these animals,” Baker told a New York Times reporter in 1996, the year their study was published in the journal Nature, “is hundreds and probably thousands of times greater than normal.” Only, as they write looking back in 2006, “Lesson 1: Beautiful theories are often destroyed by ugly facts”: the findings didn’t hold up. All that variation, it turns out, was generated long before the catastrophe, long before Chernobyl, and long before the USSR. Rather than compressing “several thousand years of evolution into a decade,” as a colleague wrote in an article accompanying the study, it was instead the outcome of the natural process of selection and evolution. A few agonizing weeks after the researchers realized their mistake, thanks to a more accurate analysis of archived samples, they voluntarily retracted their Nature paper. Still, the group continued seeking evidence of Chernobyl’s signature on life in the zone. But rather than twisted mutants and double-headed voles worthy of B-movie status, studies by Brenda Rodgers, also from Texas Tech, showed an even more surprising effect—life went on, seemingly normally. Rodger’s studies pointed not to wholesale mutation but rather to physiological acclimatization. The voles, in effect, adapted by becoming primed for life in a radioactive exclusion zone (which, Chesser points out, is classified as “chronic low-dose” radiation.) One explanation for physiological adaptation is hormesis, a sort of “rebound effect” that can follow an initial disruptive or stressful event like exposure to radiation; sort of the proverbial “a little bit is good for you,” an initial small exposure may protect from subsequent exposures. “I do believe that hormetic responses are possible,” says Chesser, “and some of Dr. Rodgers’ research supports hormesis in rodents exposed to low-dose radiation.” Follow-up studies in Rodgers’s lab suggest that hormesis may protect not only exposed adults but also pups-to-be, ramping up protective enzymes and proteins in utero to prepare the fetus for a slightly more radioactive world. And this is where University of South Carolina researcher Timothy Mousseau, Anders Moller of the National Center for Scientific Research in France, and others come in. For years, Mousseau and colleagues have reported that rather than creating a virtual “wildlife preserve,” Chernobyl’s impact was as insidious and hideous as one might expect of a nuclear disaster. The team found that bird populations—barn swallows in particular—were deformed; beaks, eyes, and tail-feather coloring were impacted; and individuals developed smaller brains. The effects were so detrimental, suggested Mosseau and Moeller, that the population was unsustainable, made up of deformed natives and immigrants from less impacted regions. But now, despite intense mutual skepticism of each other’s work, the findings of the two groups seem to be converging—at least for some species. Ismael Galvan, Mousseau, Moller, and others are finding that although some bird species may be feeling the heat others are managing, as suggested earlier by Chesser and colleagues’ work with voles. Birds are adapting, possibly through hormetic changes, enabling inhabitants of Chernobyl’s zone to tolerate radiation that would make others sick. Normally, this kind of physiological acclimatization tends to protect the individual, but not necessarily its offspring, just as our own decision to exercise, toss back a single glass of wine, or maybe even take in just a little bit of sun—actions that might benefit us—won’t help our kids. Yet some signals leading to protection may be passed on to offspring, as they were in Rodgers’ mice. “We believe that epigenetics are behind the response we detected in birds,” says Galvan. Epigenetics refers to changes in gene expression not caused by changes in the actual genetic code. It’s not hard to imagine some interplay between epigenetics and hormesis. Whether or not epigenetic changes can be passed from generation to generation ad infinitum remains an unknown. But they most certainly can be passed from one generation to the next. I asked both Chesser and Galvan about the potential for evolution in response to radiation. In the scheme of life, it isn’t such an outlandish idea—life had to make its peace with radiation in order to survive on Earth in the first place, and there are plenty of examples of life, even vertebrates, evolving within our lifetimes in response to human activity. Galvan says evolution is one possibility. “On plants from Chernobyl they have found that chronic exposure to ionizing radiation affects the expression of genes that control DNA repair. This would make that environmental exposure to ionizing radiation induce changes that may be transferred to the offspring, generation after generation. For now this is just speculation.” Chesser isn’t sure. He points to Rodgers’ research on rodents. “I will be careful to point out that this is not ‘adaptation’ in the strictest sense, but rather physiological acclimatization. Traditionally, adaptation requires natural selection that conveys genetic changes that bestow advantages to descendants.… It should also be noted that the radiation doses even in the most contaminated habitats at Chernobyl are classified as ‘chronic low-dose’ for animals living there. Thus, it is highly improbable that any selection pressure is sufficient to cause substantial genetic change in a few generations.” The footprint of humanity on the planet is large: The chemicals we use, land we have altered, and radiation we have released are changing the world. In many cases our activities are influencing the course of evolution, imposing powerful selective pressures. We are leaving our mark upon the genomes of bacteria, bugs, and countless other animals as they evolve in response to human activity. Whether this is the case for voles, birds, and other small animals living within the Exclusion Zone is not yet clear—although I wouldn't be surprised if one day someone finds not just adaptation, but evolution in response to radiation. In either case, for all those species that do manage, either evolving or adapting or just scraping along until conditions improve, there are plenty more that cannot. It is too early to know whether life is evolving in response to radiation or individuals are simply adapting—biding their time, surviving until the radiation fades. Yet in comparison to even our most persistent chemicals, Chernobyl’s radiation is here to stay for the long run. In a twisted way, the fact that life goes on in a place that sends the Geiger counter buzzing—whatever the mechanism—is hopeful. We are making a mess of our one and only home planet, but life will go on—with or without us.