If your lungs are working properly, you probably don’t think about them all that much. They’re pink. There are two of them. Smoking makes them sad. What else is there, really?
Well, did you know your right lung is bigger than your left, which has to share space inside your chest cavity with the heart? The right one is also built up of three lobes, while the left has only two.
And while breathing in and out seems like the most obvious thing in the world, something we all have in common, a gander around the animal kingdom reminds us that life is anything but simple.
Consider the Fitzroy River turtle, a native of Australia. Turtles have lungs that pull oxygen out of inhaled air, just like you and I do, and yet lab tests show the juveniles of this species can stay underwater for at least 72 hours. How do they do it? They utilize a highly sophisticated gas exchange apparatus known as their butts.
I’m being serious. Fitzroy River turtles have tiny, specialized papillae lining the walls of their cloaca—the one-stop-shop turtles use for urination, defecation, sex, and egg-laying. These papillae act somewhat like the alveoli in our lungs do, siphoning off oxygen molecules and absorbing them into the bloodstream. These baby turtles breathe through their butts.
Things get even weirder when you look at other reptiles.
“Most snakes have only one fully functional lung,” says Harvey Lillywhite, author of How Snakes Work. Lillywhite, of the University of Florida, explains that most of the organs in snakes have become cigar-shaped over the millennia, and the lungs are no exception. As in humans, the left lung seems to have gotten the short end of the stick. The left lungs are so shrunken in some species of snake, in fact, that they’re considered vestigial, leftovers from a time when they used to serve more of a critical function.
There’s actually still a lot we don’t know about how animals breathe. But we’re getting closer to understanding thanks to a scientist named Colleen Farmer and her experiments with live alligators and disco fog.
Alligators have weird innards. They have “teeny, tiny hearts because they’re aquatic, ectothermic, sit-and-wait predators,” says Farmer, a comparative physiologist at the University of Utah. They don’t need big, strong hearts like endurance athletes. But their lungs are huge. Weirder still, the lungs are intricately connected to the pericardium, the sac that contains the heart, something you don’t see in other animals.
As she was dissecting an alligator one day, Farmer says, an explanation dawned on her: Each beat of the heart could be tugging on the lungs in such a way as to stir up the air already inside, effectively circulating air to more areas where blood vessels can grab oxygen. If true, this breath by heartbeat (so to speak) would be a handy trick for a predator that likes to sit very still for hours on end—it could literally hold its breath while waiting to ambush its prey.
Just one thing: How do you test the fluid dynamics of airflow inside the body of a reptile?
Well, if you’re Farmer, you concentrate disco fog vapor in an e-cigarette, attach it to some tubing, and shotgun the vapor into a live alligator. Using an endoscope, she could watch the fog roll through the gator’s respiratory system. (“How’s work?” asks Grandma at Thanksgiving. “Oh, you know, same old, same old.”)
Farmer found that, in two minutes of holding its breath, an alligator can circulate the same amount of oxygen throughout its lungs using this “cardiogenic flow” as if it were sucking in fresh air.
Bird lungs look nothing like alligator lungs or human lungs for that matter. Open up a bird and you’ll find air sacs that look like bubbles made out of pink Saran wrap. And there are tons of them! Air sacs that push up into the neck, air sacs extending into the wings, air sacs down by the tail.
“There are just air sacs all over the place,” says John Hutchinson, professor of evolutionary biomechanics at the Royal Veterinary College at the University of London. “Pretty much everywhere there isn’t other stuff, there are air sacs.”
Anyway, all of these air sacs connect to the lungs in a closed circuit. This means that when a bird breathes in, the air doesn’t just come in and out again. It flows through a one-way network of tubes that get smaller and smaller. This unidirectional flow is a far more efficient way to breathe than passing air in and out through the same routes and a system long thought unique to birds.
However, Farmer is finding that unidirectional breathing—not to be confused with Tenacious D’s “inward singing”—may be a lot more widespread than we thought. She found it in her alligators: Their heartbeat-driven breathing only works because their lungs have tiny valves that coax air in one direction. She has since rigged up respiration experiments with monitor lizards and green iguanas and shown that both are also capable of unidirectional breathing. Next she wants to look at tuataras, turtles, and amphibians to see how deep the deep breathing goes.
Of course, if amphibians are capable of unidirectional breathing, it may well be the least bizarre trick in their repertoire. Many amphibian species can breathe through their skin, wicking oxygen out of the air like the weird little mutants that they are. And salamanders are weirder than most.
“There’s tremendous diversity in salamander respiration,” says Hutchinson. “They go through metamorphic transition where they transform from gill-breathing larvae to lung-breathing adults.”
And then some species have just given up on the whole lung enterprise. These salamanders, of the Plethodontidae family, breathe entirely through oxygen absorbed through their skin and the roof of their mouth. Best of all, you don’t even have to travel to some deep, dark jungle to find a lungless sally. Just go to Indiana.
Even amphibians that don’t breathe through their skin breathe strangely. We breathe by creating negative pressure inside our chest to suck in air, sort of like how a turkey baster draws all those delicious juices into its bulb. But frogs go the opposite way, says Farmer. They take two or three little gulps of air into their mouth, plug up their nostrils, and then shove that air down into their lungs.
Of course, birds, reptiles, and amphibians don’t have a monopoly on weird breathing. Mosquito larvae live underwater but breathe air through what can only be described as a butt snorkel. And a predator of mosquito larvae, the diving bell spider, is able to spend much of its life underwater by keeping air bubbles attached to its chest with tiny, hydrophobic hairs.
Mammals also have some fascinating representatives. Arctic ground squirrels go so stone-cold when they’re hibernating, you can seal them inside jars of noxious gases without making them stir.
Walruses and other marine mammals can store a ridiculous amount of oxygen in their blood and muscle thanks to enhanced levels of hemoglobin and myoglobin.
“It’s their own on-board scuba tank,” says Shawn Noren, an associate research scientist at University of California, Santa Cruz.
Male walruses also have large air sacs in their head and neck that they inflate during mating—“I guess the females find them sexy,” says Noren—though the floaties may also be used in the water for buoyancy.
Understanding how respiration works could change the way we think about how and why our ancient ancestors first made the lurch from sea to shore—and in some cases back again. In fact, whales—marine creatures that evolved from terrestrial creatures that evolved from marine creatures—may have the most bizarre breathing apparatuses of all. Through millions of years of evolution, their windpipes migrated into blowholes in the middle of their backs. Breathtaking.