by Matt Simon
You see, when the pink fairy armadillo is burrowing, just a half foot underground, it doesn’t get the relatively stabilized climate that deeper burrowers get, farther removed from the elements. When the soil heats up in the day, the armadillo heats up, and when temperatures plummet at night, the armadillo freezes. Critters aboveground seek shade for coolness or huddle together for warmth, but the pink fairy armadillo has no such luxuries. Instead, it has turned its armor into a delicate, flimsy radiator that serves as no protection from predators whatsoever.
People hate it when I tell them this, since it tends to spoil the charm of the pink fairy armadillo, but its shell is pink on account of the blood showing through. A whole lot of blood. It shows through because, like many subterranean creatures, the armadillo has no need for lots of melanin, the dark pigment that helps protect skin like ours from UV damage. All that blood is swirling around in the shell to help the armadillo thermoregulate. By virtue of being a mammal, its body maintains a certain temperature, but because sweating ain’t going to do it no good nohow down in the dirt, the armadillo has evolved a different solution. If it needs to lower its temperature, it can pump blood out of its core and into the shell. This cools the blood just like a car’s radiator would do for engine coolant, only the armadillo is using the soil above it as the agent instead of air. Should the armadillo need to warm up when temperatures drop at night, it can pull the blood out of the shell and add it back to its core.
Now, it seems counterintuitive for desert temperatures to fluctuate so dramatically—and rapidly, for that matter—when you’d expect the environment to be hell-hot around the clock. But it all comes down to moisture. Deserts like the one the pink fairy armadillo calls home of course have little of it, both in the land and in the air. The problem is that moist air holds heat well, which is why the climate is stable day and night in the tropics. But in the dry air of the desert, the heat quickly dissipates. That’s great for the beasts that emerge only at night to hunt or graze, kicking back underground or in shrubbery by day.
FRIENDS, ROMANS, COUNTRYMEN, LEND ME YOUR EARS
The using-blood-to-cool-off strategy has evolved independently in all manner of desert dwellers. When you see an elephant flapping its ears, for instance, it’s probably trying to cool down, because those things are packed with blood vessels. Kangaroos, too, will lick their arms, which are—you guessed it—loaded with blood vessels. The same goes for the absurdly enormous ears of the fennec fox. Seriously, they’re ridiculous. The animal looks like a huge pair of ears with a body tacked on as an afterthought.
While biologists believe the pink fairy armadillo to be largely nocturnal, the animal isn’t about to go running around in the cool air. This is because it’s essentially worthless aboveground, and I say that with all due respect. It takes moxie to live your entire life crawling through the dirt, hoovering up bugs and roots and such. Out in the big bad world, though, being ghost white isn’t ideal, and having stubby legs and cumbersome claws doesn’t help either. So the pink fairy armadillo probably surfaces only when it rains—according to locals who have had the honor of glimpsing the tiny rarity—in part because its burrows can flood, but also because the moisture is a detriment to thermoregulation. (The aforementioned armadillo expert Mariella Superina once filmed a nature special in which the crew sprayed the desert with jets of water, hoping that’d force the creatures out. It didn’t work, but I’m sure the plants at least appreciated it.) In addition to relying on that rosy shell to maintain its body temperature, the armadillo also must keep its luxurious fur dry or risk freezing to death.
My apologies. This is getting depressing. It’s no way to treat one of the most charming, most magical creatures on Earth. So I must say: Far beyond the radiator shell, the pink fairy armadillo is marvelously fit for life in the arid underworld. But if it wins for Most Adorable Subterranean Desert Mammalian on Earth (we’re working on the name), there must be a second place . . . and a third place . . . and a dead last.
Our next burrower is definitely a dead last.
Naked Mole Rat
PROBLEM: The life of the burrower is plagued with tight squeezes.
SOLUTION: The naked mole rat has evolved extremely stretchy, loose skin that allows it to move better in its tunnels. Oh, also: The starch that makes this possible, hyaluronan, bestows the animal with a near immunity to cancer.
Now’s as good a time as any to announce that I have an excessive amount of elbow skin. Not anywhere else, mind you—just my elbows. I can pull on it and it’s, like, kinda stretchy. I’m ready to admit that.
If my elbow were an animal, it’d be the naked mole rat. Whereas the pink fairy armadillo is darling, the naked mole rat is pretty much a wrinkled sausage with way too much skin and massive buckteeth that grow outside of its lips, allowing the creature to gnaw through the dirt without choking to death. To its credit, though, the naked mole rat is not entirely bare: It has fine hairs here and there on its saggy body that function as sensory whiskers down in the blackness. Thus, it has no real use for eyes, so they’ve atrophied into beady little peepers. It isn’t hard, then, to understand why the beast comes in dead last in the competition for Most Adorable Subterranean Desert Mammalian on Earth.
Now, when I was talking about the pink fairy armadillo I mentioned other tactics that subterranean animals use to deal with the heat and cold: burrowing deeper and huddling together. The naked mole rat does both of these. It lives in societies of as many as three hundred individuals, in a complex system of tunnels that go down to six feet deep, compared to the pink fairy armadillo’s modest six-inch-deep burrows. Should things cool down, the naked mole rats can huddle together in their chambers. And should things heat up, they can retreat deeper into the burrow where there’s some measure of climate control.
THE EYES HAVE IT
It’s common for critters that live in caves or burrows to have either atrophied eyes or no eyes at all. These may seem like structures evolution would want to hold on to just in case, but keep in mind that it takes a whole lot of energy and resources and time to build such things. Having the eyes evolve away frees up all this for other pursuits, plus it’s one less thing to get injured or infected, which is a particularly big problem when you’re rooting around in the muck. Accordingly, the blind mole rat, another burrower that isn’t related to the naked mole rat, has done away with its eyes almost entirely by growing fur over them. It’s a bit like wearing sunglasses all the time, only they’re made of skin—and you can’t take them off. All right, maybe they’re nothing like sunglasses.
And indeed, the tunnels of the naked mole rat are busy places to be, with creatures shuffling around like blood cells coursing through veins. The routes can be exceedingly narrow, and this could well have driven the evolution of the burrower’s floppy skin. Being so loosey-goosey allows the naked mole rat to more efficiently squeeze through its tunnels without shredding its skin—not an unwelcome adaptation if you’re trying to escape predators that are penetrating your bunker.
The stretchiness is all thanks to a starch called hyaluronan. In animals it helps form what’s known as the extracellular matrix—a network of sorts that holds all our cells together—and is part of the reason why I can do weird things with my elbow skin. But in a naked mole rat’s skin, hyaluronan molecules are ten times longer than our own. Thus the naked mole rat’s entire surface is highly stretchy. This unique solution to a problem seems to have imparted a welcome side effect on the critter: A naked mole rat will almost never get cancer.
Normal hyaluronan, in, say, us humans, communicates with cells and tells them to divide. But the elongated hyaluronan molecules in the naked mole rat prevent cells from dividing. And that’s a cancer researcher’s dream. Simply put, cancer is the abnormal division of cells, which isn’t happening in the naked mole rat’s body. If scientists can figure out how to supercharge the hyaluronan in our own bodies, they may be able to prevent the runaway growth of tumors. While the
research is still in its infancy, one day the naked mole rat could lead science to huge breakthroughs in the fight against cancer.
Having a near immunity to cancer is great and everything, but you might be thinking that being naked is somewhat of a handicap. And you’d be right. But this is where the huddling comes in. Naked mole rats get pretty intimate down there in their burrows, amassing in congregations that sometimes grow to four individuals deep. Yeah, it sucks to be the ones down there at the bottom gasping for air, but these creatures have evolved a tolerance to low oxygen. And without the warmth of the crowd, individuals would perish when temperatures plummet at night.
That’s because even though the naked mole rat is a mammal, it can’t regulate its body temperature. While it would appear to be a waste to throw away the ability to maintain a constant temperature—known as homeothermy—it’s not all it’s cracked up to be. Sure, reptiles have to burn time sunning themselves each day to warm up, but for mammals, maintaining an internal furnace is extremely energy intensive. That fire demands fuel, which is in short supply for naked mole rats as they burrow around hoping to stumble upon a tuber to chew on. Indeed, the energy cost for burrowers to find food can be as much as four thousand times that of surface dwellers. So to cut back on energy consumption, the naked mole rat seems to have forsaken its homeothermy in favor of cuddling.
And there’s no greater cuddler than the queen. Just like the pistol shrimp, these animals form a rare (for a noninsect, at least) eusocial society ruled by a matriarch, who’s longer than her subjects because the spaces between her vertebrae expanded when she came into power. She’s the only female that breeds, and she moves through the colony each day asserting her dominance by biting everyone else and giving them a good shake. But being both a ruler and a busy mom with embryos to worry about, she needs to be sure her body temperature is ideal, so she spends more time lazing in the huddles than any other individual.
A ONE-TRACK-MIND KIND OF PERSON WHO LOVED TO BE SCRATCHED
Another much larger mammalian burrower is the wombat of Australia, a stocky teddy bear of a creature that you can’t help but want to befriend. And in fact at least one naturalist has. In an account from 1963, Peter J. Nicholson describes crawling through their burrows and making the acquaintance of a young male. “Occasionally he would come up to me and sniff my arms and examine my face and hair inquisitively while I imitated his friendly grunt,” he wrote. For three months the pair followed each other around, sometimes sitting at the edge of the burrow taking in the day, perhaps with an air of introspection. “He gave me the impression of being an intelligent, one-track-mind person,” Nicholson concluded, adding that he “used to love to be scratched.”
Between losing its ability to regulate its body temperature and largely losing its eyes, the naked mole rat is a reminder that there’s no such thing as “progress” in evolution. (Darwin resisted using the word “evolution,” from the Latin meaning “unfolding” or “unrolling,” because it might imply some sort of march toward perfection. He preferred “descent with modification.”) Sure, over the 3.8-billion-year history of life on Earth organisms have gotten more and more complex since that initial primordial soup of microorganisms, but intricate evolutionary innovations like the eye can fade away when they’re not needed. Darwin’s idea here that species don’t necessarily become perfect, only well adapted to their environment like the seemingly backward naked mole rat, wasn’t . . . how should I say this . . . well received. It meant that humans were just another animal that happened to evolve an impressive mind, not a creature favored by a higher power. He was right, though. We’re not special, however much we think we are. We’re naked like the mole rat—only we invented clothes.
CHAPTER 5
Turns Out Getting Eaten Is Bad for Survival
In Which Fish Choke Sharks to Death with Snot and Geckos Do Their Best Impression of Leaves
The statistics don’t lie: Getting eaten is a leading cause of death in the animal kingdom. It’s been that way for the eons that life has graced the Earth. Which is a whole lot of time for evolution to come up with some impressive solutions to the problem of predation. There’s a salamander, for instance, that can regrow entire limbs that predators (or its salamander friends) have made off with. And yes, in case you were wondering, its secrets could one day get us humans to regrow our limbs as well.
Hagfish
PROBLEM: Sharks are pretty much just giant teeth wrapped in bad attitude.
SOLUTION: The eel-like hagfish chokes its attackers to death by filling their gills with copious amounts of snot that it ejects out of glands in a fraction of a second.
Say what you will about crummy neighborhoods, but at least they’re consistent. They can be extremely hot and dry or frigidly cold, you can be sure of that. But an organism can adapt to these things, for something like a desert is predictable. More befuddling, though, are the predators evolving right along with you, adapting to your adaptations, developing bigger teeth if you develop armor, or better senses if you get stealthier. And it’s in response to these fiends that evolution starts getting really creative with its solutions. Like, evolving-to-choke-sharks-to-death-with-your-snot creative.
It got a bit shortchanged with its name, and the hagfish deserves more respect. The eel-shaped creature is a denizen of the seafloor, where it hoovers up worms and partakes in the occasional fish carcass. And when the hagfish comes upon such a bounty, the scavenger will use it for everything it’s worth. It’ll burrow into the body and consume the carcass from the inside out—and not just with its mouth. The hagfish’s skin will absorb the nutrients given off by the rotting flesh.
But here’s the problem. If the hagfish has its face buried in a carcass all day, and its eyesight is for the most part worthless, it’s at the mercy of the deep’s predators, including sharks and fish and eels. And quite frankly the hagfish looks pretty tasty, on account of being a wiggly tube of flesh. Luckily, though, it has one of the more novel defenses in the animal kingdom: weaponized snot.
The hagfish’s sneeze is a sneeze to be reckoned with. Its body is packed with over one hundred specialized slime glands, and should you be unfortunate enough to so much as rub up against the creature, these glands work in concert to immediately spew a swirling cloud of goop. That might not seem like a big deal to you and me, say if you had the honor of handling one in a tank and playing with its slime (yes, scientists get paid to do that, and I envy them for it). But for a creature with gills, like a hungry shark, this could mean death by suffocation.
The slime is a very special one indeed, and more on that in a second, but first we should talk about how gills work. Think of them as lungs turned inside out: Just as our lungs have structures that are packed with capillaries, where the blood pulls in oxygen from the air, fish gills are packed with capillaries that make direct contact with the water. We humans have to keep air flowing through our lungs at all times and fish have to do the same with their gills, so they can’t just lie there and expect to gather enough oxygen. This is why you’ll see fish gulping—that’s them pushing water over the capillaries. (Sharks have to swim around to keep the flow going, but it’s a myth that they’ll all drop dead if they stop swimming. Open-ocean species need to, sure, but other varieties, ones that rest on the seafloor, will instead gulp air like their bony-fish cousins.)
A SLEEPING BAG OF SNOT
The parrotfish calls the more paradisiacal coral reef its home, but it ain’t about to wait for an attack to unleash its own cloud of snot. When it falls asleep among the corals, it secretes its own sleeping bag in the form of an enveloping cocoon of mucus. Should a predator come sniffing around, that snotty sleeping bag could well restrain the parrotfish’s scent. Plus, it doubles as an alarm system if something literally invades the fish’s personal bubble. So while you may not appreciate snot, there are at least two creatures on this planet that certainly do.
So, the slime. Each of those hundred-plus slime g
lands is packed with two different kinds of cells. One type produces your run-of-the-mill mucus, but the other ejects incredibly strong threads that are each six inches long. I’ll reiterate. A microscopic cell that measures 0.004 inches long by 0.002 inches wide fires out a thread a half foot long. That’s . . . infuriatingly illogical.
But it works. The secret is how the thread is packed, spun precisely around and around on itself to form an oblong yarn ball held together by a water-soluble glue. When the hagfish is in trouble, it contracts the muscles around the slime glands, ejecting the mucus and the thread bundles, which unravel as the glue dissolves in the water. The released energy from the bundles helps inflate the cloud, which only gets bigger as the hagfish flops around trying to escape.