Sadly, we live in a world where a few individuals have the power to wipe out civilisation as we know it with nuclear weapons. We hope that power never gets used, as most of us living things wouldn’t make it far in a radioactive wasteland. Among other hazards, exposure to ionising radiation has both short- and long-term health effects, thanks to the way it scrambles our DNA.
But the world is full of survivors. Some lifeforms have hardly changed over millions of years, while other, newer creature designs have developed out of long, complicated evolutionary processes. When it comes to a post-nuclear world, organisms in both categories stand chances of survival.
This list is made up of species whose radioresistance, or their ability to withstand radiation, has been tested by scientists. None are mammals — the fleshier you are, generally, the less hope you have — but hey, we had a good run.
Animals that can exist without water tend to do well against radiation. This pattern is seen in multiple extremophiles, the official term for animals that can handle conditions that would be deadly to most organisms. One such extremophile is the sleeping chironomid fly, or Polypedilum vanderplanki. The fly’s larvae are laid in shallow pools in parts of semi-arid Africa and need to be able to survive even if their cribs dry up. In that desiccated state, research has shown that the flies can withstand other stressors — like gamma rays — with stupendous success. In fact, the larvae handle compounding stressors with ease once dehydrated. Let’s hope they don’t get any ambitions beyond their stress-ridden nurseries.
Made famous to kids everywhere by Spongebob Squarepants, nematodes are as minuscule as they are abundant. Nathan Cobb, an early nematologist, perhaps put it best in his 1915 work, Nematodes and their Relationships: “If all the matter in the universe except the nematodes were swept away, our world would still be dimly recognisable… we should find its mountains, hills, vales, rivers, lakes, and oceans represented by a film of nematodes.” Delightful!
Nematodes, it turns out, can survive big doses of gamma radiation. (Perhaps the most unfortunate thing about being an extremophile is that scientists will try rapturously to find your breaking point.) With nematodes, specifically C. elegans, their ability to handle radiation exposure has to do with the radioactive isotope at play. Some radiation, though, can cause reproductive problems in the wriggly little nematodes (it can prevent them from producing sperm cells), so perhaps they wouldn’t win in an ultimate showdown in a nuclear world.
In the 1960s, numerous experiments put scorpions’ skills at handling radiation exposure to the test. They made good candidates. Similar to other extremophiles, scorpions can be frozen solid and survive, for example, and the invertebrates were known to handle UV radiation with ease, glowing from it as if to say, “Is that the best you’ve got?”
Thanks to these experiments, we know the radioresistance of a couple of scorpion species. How long each lasted depended on the doses they got — one species couldn’t make it a week after doses of 11,500 roentgen, but another species (the fattail scorpion) was reported to resist over 50,000 roentgen. According to the U.S. Nuclear Regulatory Commission, it would take about 450 rem (roentgen equivalent in man) to kill 50% of a human population from exposure over 30 days. So scorpions would certainly do better than humans after the warheads went off. I suppose we can leave it at that.
This one’s a classic, though cockroaches aren’t as quite durable as pop culture might lead you to believe. The 1960s really were the heyday of entomologists blasting their study subjects with radiation — in 1963, a bunch of German cockroaches were hit with ionising radiation in a lab setting. Between 64 and 94 Grays (a unit for measuring radiation doses) was all it took for the six-legged speed demons to keel over and quit their mortal coils. By comparison, 8 Grays is enough to kill a human, according to an International Atomic Energy Agency report.
It’s not like all insects are extremophiles. Low numbers of butterflies and spiders have been reported at Chernobyl since the 1986 disaster. General consensus is that insects tend to fare better than mammals under radiation stress because of DNA repair mechanisms. Cockroaches would outlast us in a fallout situation, sure, but they’re hardly indestructible.
Now we’re getting into the heavyweights of radioresistance, where larger organisms just can’t compete. The most radioresistant animals on Earth are tiny and generally more recently studied. Take D. radiodurans, a plucky little bacterium first discovered in some canned meat exposed to X-rays in 1956. The bacterium handles 15,000 Grey like a walk in the park.
Not only does D. radiodurans survive under copious amounts of radiation exposure, according to one paper, it experiences “luxuriant growth in the presence of high-level chronic irradiation.” In other words, this bacterium will outlast us all.
Tardigrades only broke into the mainstream discourse a few years ago, but since then, these water bears (also nicknamed moss piglets) have never ceased to amaze. While they endure extreme environments, these microscopic animals can be found most anywhere — one species was discovered in a parking lot. Just as insects are good at DNA repair, tardigrades are good at threat mitigation. As Thomas Boothby, an extremophile expert at UNC-Chapel Hill, told the BBC in 2015, it comes down to their ability to recover from dehydration, just as the sleeping chironomid larvae do. “Since water bears can survive drying,” Boothby said, “they must have tricks for preventing or fixing the damage that cells like ours would die from.”
In October, a new troupe of tardigrades were found to have a radiation shield that makes them even more resistant than the C. elegans nematode. Before that, a tardigrade protein was found to help human cells to resist X-ray radiation.
Say hello to Macrobiotus shonaicus, a completely new species of tardigrade – those incredibly resilient microscopic wee beasties that likely have what it takes to survive the apocalypse.Read more
Alright, here we are. Lucky number seven. And we’ve saved the most radioresistant for last. As its name suggests, Thermococcus gammatolerans is good at handling gamma radiation, both in reducing the extent of DNA damage induced by radiation and in its ability to repair damaged chromosomes. (It’s fitting, perhaps, that it’s a select few single-celled organisms that would fare best in a nuclear apocalypse, rather than the sort of complex lifeforms that would invent such bombs in the first place.)
In 2016, researchers dosed the microbe with 5,000 Grey, and it shrugged. But that was just to get a better understanding of how the organism was able to resist the radiation on a genetic level. The extremophile’s real feat occurred in 2003, when it was first identified. Found among hydrothermal chimneys in the Gulf of California, T. gammatolerans grew even when subjected to a whopping 30,000 Grays of gamma radiation. (Again, the lethal dose for 50% of a human population in 30 days is 4.5 Grays. So, not even remotely close).
Even when nematodes, E. coli, and perhaps even tardigrades have gone the way of the dodo, it seems that bacteria like T. gammatolerans could still hold their own. But the evolutionary path is long and winding, and we haven’t blown the world to bits just yet. Perhaps we humans just prefer death by a thousand cuts.