Tardigrades, Trisolarans and the Toughness of Life

I last wrote about extremophiles—creatures that thrive in environments that are extremely hot, cold, salty, acidic, alkaline, radioactive, and so forth—not just because these critters are interesting in themselves (although they assuredly are!) but also because they italicize the important reality that whereas individual lives are often fragile, life itself is not. And this, in turn, serves to undermine the claim that the existence of living things is itself “proof” of divine intervention.

What follows is a bit more info about those extremophiles, material developed at greater length in my book, Through a Glass Brightly: using science to see our species as we really are.

Most extremophiles are microbes, but not all. There are, for example, a group of wingless, mostly eyeless insects known as grylloblattids, more commonly ice-bugs or ice-crawlers. They live, as you might expect, in very cold environments, typically under frozen rocks. My personal favorites, however, are tardigrades. These multicellular creatures are rarely more than one millimeter in length and often invisible to the unaided eye. They have four legs along each side, each outfitted with tiny claws. They also have a clearly discernible mouth and are quite adorable.

Purists don’t include tardigrades among extremophiles, since they do not appear adapted to extreme environments per se—i.e., like us, they do best in comparatively benign conditions, which, in the case of tardigrades includes the moist, temperate mini-world of forest moss and lichens. Their probability of dying increases in proportion as they are exposed to highly challenging circumstances, so unlike classic extremophiles, they are evidently adapted to what human beings, at least, consider moderate circumstances.

However, tardigrades are extraordinary in their ability to survive when their environments become extreme. Not only that, but whereas typical extremophiles specialize in going about their lives along one axis of environmental extremity—extreme heat or cold, one or another heavy metal, and so forth - tardigrades can survive when things get dicey along many different and seemingly independent dimensions, simultaneously and come what may. You can boil them, freeze them, dry them, drown them, float them unprotected in space, expose them to radiation, and even deprive them of nourishment—to which they respond by shrinking in size. These creatures, also known as water bears, are featured on appealing t-shirts with the slogan “Live Tiny, Die Never,” and a delightful rap song describing their indifference to extreme situations is titled “Water Bear Don’t Care.” These little creatures might be the toughest on Earth.

You can put them in a laboratory freezer at -80 degrees Celsius, leave them for several years, then thaw them out and just 20 minutes later they’ll be running around as though nothing had happened. They can even be cooled to just a few degrees above absolute zero, at which atoms virtually stop moving; once thawed out, however, they move around just fine.

Admittedly, they aren’t speed demons; the word “tardigrade” means “slow walker.” But wimps they aren't. Exposed to super-heated steam (140 degrees centigrade), they shrug it off and keep on living. Not only are tardigrades remarkably resistant to a wide range of what ecologists term environmental “insults” (heat, cold, pressure, radiation, etc.) they also have a special trick up their sleeves: when things get really challenging – especially if dry or cold - they convert into a spore-like form known as a “tun,” which can live (if you call their unique form of suspended animation “living”) for decades, possibly even centuries, and thereby survive pretty much anything that nature might throw at them. In this state, their metabolism slows to less than 0.01% of normal.

Given that they possess the kind of powers we otherwise associate with comic book superheroes, it might seem that tardigrades are creatures out of science fiction, but the connection could well be the other way around. The Three Body Problem is a blockbuster that has broken all records for sci-fi literature in China, and that in 2015 became the first book not originally published in English to win the coveted Hugo Award for best sci-fi novel. It describes extra-terrestrials known as Trisolarans, whose planet in associated with three suns, the interactions of which—as physicists and mathematicians understand (in real life)—would generate chaotically unstable conditions.

Trisolarans, therefore, are unpredictably subjected to extreme environments depending on the temporary orientation of their planet relative to its chaotically interacting stars: sometimes lethally hot, other times cold, sometimes unbearably dry and bright, other times dark, and so forth. As a result, these imagined extremophiles have evolved the ability to desiccate themselves, rolling up like dried parchment, only to be reconstituted when conditions become more favorable.

I have not been able to determine whether author Liu Cixin was aware of real-life, Earth-inhabiting tardigrades when he invented his fictional Trisolarans, but the convergence is striking.[1] (In the interest of scientific open-mindedness it should also be considered that perhaps tardigrades are real Trisolarans, refugees from a planet that was chronically exposed to intense environmental perturbations. This would explain the puzzling fact that tardigrades appear hyper-adapted, able to survive to extremes that greatly exceed what they experience here on Earth.)

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In any event, tardigrades have two more arrows in their extremophile quiver, neither of them shared with Mr. Liu’s Trisolarans. More about these remarkable—and very real—living things in my next post.

[1] My guess is that he wasn’t; Mr. Liu is masterful when it comes to physics, but with biology (or, for that matter, psychology) ... not so much.