Superlative

The cheetahs at the Ensessakotteh wildlife refuge went through hell before arriving at the conservation and education center run by the Born Free Foundation in central Ethiopia.

Poachers had killed their mothers. Smugglers had stuffed them into tiny crates, wicker baskets, and buckets without air holes, apparently intending to transport them to the Middle East, where they have long been prized as pets. Ethiopian authorities ultimately rescued the cubs, but not before many of their siblings had died.

When I learned their story, it seemed to me that the cats I was about to meet would be shells of the ones they could have been had they not been stolen from the wild. I was joyfully mistaken. The Ensessakotteh cheetahs may have been robbed of the maternal nurturing and natural conditioning they needed to fend for themselves in the bush, but they slept together in the sun, frolicked in the tall grasses between the trees, and took prowling crouches when wild crows and hawks dared to land nearby.

And as the sun began to dip and it became time to feed, they did what cheetahs are born to do.

There is no way to adequately describe the power of a cheetah’s first steps into a sprint. It is as though their entire bodies have been drawn back, like an arrow on a bow, and then released into the wind. Nothing so explosive should be so quiet, and yet they run with barely a sound, just the swishing of grass against their backs and the scratching of dirt beneath their feet.

Every schoolchild can tell you that cheetahs are the world’s fastest animal. But fastest is a quirky concept. Quirkier even, perhaps, than biggest, smallest, or oldest—for there are hundreds of ways to think about speed.

For years we called Usain Bolt “the world’s fastest human” because he was nearly untouchable in the 100-meter dash, but if you had put him in a mile race with Taoufik Makhloufi, or a marathon with Eliud Kipchoge, or an ultramarathon with Kathleen Cusick, Bolt would have been left in the dust.

Put any of those people in a pool with swimmer Katie Ledecky. Or put Ledecky in open water, next to long-distance phenomenon Chloe McCardel. Or put McCardel in an airplane, and let her dive out the door alongside record-holding speed skydiver Henrik Raimer. You’d have a different “fastest” every time.

There is no world’s fastest human, because there are different ways to measure speed in humans. And there are even more ways to measure speed in the rest of the natural world.

Cheetahs are remarkable beasts. They can exceed 60 miles per hour in very short bursts. (The land speed record for a 100-meter dash was set by a cat named Sarah in 2012; she reached a top speed of 61 miles per hour in that sprint.) When researchers collared five wild cheetahs, though, and tracked their running habits, they learned that the cats usually run at only about half that speed, and can only do that for a few hundred meters. Then they’re done, often for the rest of the day.¹

So, no, Acinonyx jubatus isn’t really the world’s fastest animal. In most ways of thinking about speed—the rate at which an object covers distance—it’s not even close.

But to see a cheetah run is to stop caring about any of that. Because to see a cheetah run is to witness perfection of design, from nose to tail.

Let’s start up front. Most cats have a relatively small nasal cavity, consistent with predators that prioritize other senses over smell. In the cheetah skull, though, the nasal cavity is a gaping hole. In this way, a cheetah is a lot like a fighter plane.

When the Navy wanted to make its workhorse jet, the F/A-18 Hornet, even faster, one of the first things it did was make the aircraft’s intake ramps bigger. This allowed for more air to flow into the airplane’s compressors, which increase the pressure of air as it moves through the engine’s combustor. More airflow means more thrust. The Super Hornet was born.

Animals work in a similar way. Air, after all, carries oxygen, the life-sustaining gas we need, and must constantly replenish, in order to function.

Of course, it doesn’t do much good to bring in more air if there’s nothing that can be done with it. So a cheetah’s thoracic cavity is filled to the brim with big lungs, a hefty heart, and a large liver with which to take in, move, and use that oxygen to mobilize glycogen, which provides big bursts of energy.²

To keep that intake-to-engine passageway straight, and maximize efficiency, cheetahs keep their heads almost perfectly still when they are running—despite the fact that almost everything behind the cheetah’s head is moving like crazy, thanks to a spring-like spine.

Cats in general have exceptionally flexible vertebral columns; even if you don’t own a house cat, you can probably picture the classic Halloween decoration of a cat arching its back, a common feline reaction to fear. Most cats use that flexibility to stretch out their muscles—something they need to do after sleeping for three-quarters of each day or longer. Cheetahs, though, use that flexibility to stretch out their legs when they run.

To get an idea of what this looks like, cup your hand downward as if picking up a baseball, then raise your fingers up as far as you can. That’s how a cheetah’s spine flexes when its front and back legs cross, then spread apart, as it runs in a rotary gallop, a four-beat gait common to mammals. Like a spring being sprung, cheetahs shoot their legs outward, extending their spine so far that it doesn’t just straighten, but slightly reverses its curve. This allows cheetahs to extend the length of their strides. Cheetahs can cover more than 20 feet with each stride. By way of contrast, a long running stride for a human is about eight feet.

The length of those strides doesn’t come just from the spine, though. Cheetah legs include a unique one-two punch of muscle fibers that substantially differ between the front and back limbs. The back limbs have predominantly fast-twitch fibers, which can create tremendous force but have low endurance, while the front limbs have a larger share of slow-twitch fibers, which offer little force output, but are resistant to fatigue. But the cheetah’s front paws are more like its back limbs: they have a much larger supply of fast-twitch muscles than the rest of the front limbs do—allowing the cat to stay balanced at high speeds.³ Essentially, researchers say, cheetahs are like rear-wheel-drive cars with high-performance steering.⁴ And with good tires, too—at the ends of those legs are hard pads and claws that don’t retract, helping cheetahs turn at exceptionally high speeds.

And finally, there’s the tail, which might be the most amazing, and most underappreciated, aspect of the cheetah’s ability to run down its prey. When A. jubatus runs straight, its tail stays directly behind it. But when it shifts direction, even a bit, it uses the rear appendage as a whip-like counterbalancing tool. The tail snaps left, and the cheetah goes right. The tail snaps right, and the cheetah goes left. The tail snaps again, and a gazelle becomes dinner.

When it comes to speed, though, there might be something even more important than a cheetah’s design: its size.

Notwithstanding the seeming flawlessness of the cheetah’s design as a creature built for speed, at first the world’s fastest cat presented a problem for biologists trying to understand the role of speed in the animal kingdom: Why doesn’t absolute speed grow as animals increase in body size? If a house cat can run at 30 miles an hour and the larger lynx can run at 50 miles an hour and the larger-than-that cheetah can reach 60 miles an hour, why can’t the even-larger-than-that tiger run even faster?

Ecologist Myriam Hirt believes larger cats could be faster—theoretically, at least. Large animals generally have more fast-twitch muscles than their smaller peers, and would be able to use those muscles to accelerate for longer periods, if only the oxygen that supplied those muscles didn’t run out so quickly.⁵ If a tiger could dope its fast-twitch muscles with a rapid resupply of oxygen, it would likely be the fastest cat in the world by a factor that correlates to its massive body size. Alas, Hirt and her colleagues from Germany’s EcoNetLab have theorized, in the real world, the fuel needed to move a big body runs out long before a maximum theoretical speed can be reached.⁶ Their theory suggests that there’s a “sweet spot” between being big enough to take large and powerful strides and small enough to convert oxygen efficiently to muscle motion.

The theory doesn’t just work for cats. And it doesn’t just work for mammals. In fact, a focus on mammals alone may have been why this relatively simple insight wasn’t reached much earlier—the correlations are a lot less obvious when you’re looking at animals with a limited size range and a lot of other physiological similarities.⁷ So, before publishing their findings, Hirt and her fellow researchers applied their calculations to nearly 460 running animals of all sorts, including birds, arthropods, reptiles, and mammals. Plotting these creatures’ maximum speeds against their body masses resulted in an inverted J-curve that starts with tiny insects and moves upward with sublime consistency until peaking at about 60 miles per hour and 100 pounds—that’s the cheetah, of course. The curve dives from there toward larger and slower animals, like moose and hippos and elephants.

But Hirt didn’t stop with the runners. She and her team created similar plots for swimmers and flyers, again without respect to what part of the animal kingdom those creatures came from. The swimmers included birds, reptiles, mammals, arthropods, fish, and mollusks. The flyers comprised birds, arthropods, and mammals. Although the peak in speed and size was a bit different for those groups, a very similar curve appeared. In each set of animals, the as-it-gets-bigger-it-gets-faster plotline held strong until peaking about three-quarters of the way through the group, where it began to peter out.⁸

Because it holds up among animals we know, this model was quickly applied to animals we don’t know as well, including ones we’ve never actually seen. And that, I’m afraid, puts yet another blotch on the already-well-blemished science behind one of my family’s favorite movies, Jurassic Park.⁹

“Well,” the character John Hammond brags early in the first film of that fantastic franchise, “we clocked the T. rex at 32 miles per hour.”

That purported speed is put on display in one of the film’s most famous scenes, the reason I chuckle any time I notice the words “Objects in mirror are closer than they appear” on the side-view mirror on my car.

But if Hirt’s theory holds for carnivorous theropods, tyrannosaurs aren’t likely to have been able to break 19 miles per hour.¹⁰ Of course, that still makes them faster than most humans. So T. rex would still likely win a foot race with H. sapiens; it would just be a bit of a longer run before lunch.

Dinosaurs aren’t the only creatures about which we have a better understanding thanks to cheetahs, though. A lot of what we’ve learned about how animals survive over evolutionary time comes from our studies of A. jubatus.

WHY CHEETAHS SHOULD BE EXTINCT, BUT AREN’T

The Late Pleistocene extinction event was tough on the creatures of our world. By some estimates, about three-quarters of large mammals—those about 90 pounds or bigger—were lost in the Americas and Australia. In Europe and Asia, the toll was closer to half.

African animals were better at weathering the storm. Only about a sixth of that continent’s large mammals died out, but many of the rest struggled to survive. Cheetahs, in particular, were on the ropes. Their population fell so low that widespread inbreeding was the only way to survive.

Such a survival strategy, of course, has diminishing returns—as demonstrated by the last mammoths on Earth, those that survived the Pleistocene catastrophe and continued living on Wrangel Island, in the Arctic Ocean, until about 4,000 years ago. Scientists believe those woolly beasts might still be with us today if their genetic diversity hadn’t been so depleted, resulting in “genomic meltdown.”¹¹

It’s not clear whether cheetahs were still in the process of accumulating more detrimental mutations, or if they were instead in the midst of the glacially slow process of recovery, when the next big extinction event (that would be us) came along. What we do know is that the result of the Pleistocene population bottleneck is a species suffering from extreme genomic depletion in just about every measurable way, from a dearth of single-nucleotide variants, to a lack of diversity in mitochondrial DNA, to a paucity of cell surface proteins that support their immune responses. If there’s a silver lining to that latter category of genetic monotony, which is known as histocompatibility, it’s that cheetahs are very good at accepting skin grafts from other cheetahs—almost as though the cats are all siblings.¹²

And genetically speaking, they pretty much are.

When geneticist Stephen O’Brien first studied the genomes of dozens of cheetahs in the 1980s, he was confused by what he saw. “You guys did not really collect fifty cheetahs, did you?” he later recalled joking with Mitch Bush, the head veterinarian at the National Zoo in Washington, DC, who had coordinated the samples for the study. “What you actually did was to collect one cheetah’s blood then split the blood into fifty separate tubes, right?”

The cats were almost genetically identical, O’Brien wrote in his book, Tears of the Cheetah. “Their genes had the look of deliberately inbred laboratory strains of mice or rats.”

The genome sequences of wild-born cheetahs are, on average, 95 percent homozygous, perhaps the least diverse mammal genome in the natural world. By comparison, the critically endangered Virunga Mountain Gorilla is 78 percent homozygous, and the heavily inbred Abyssinian cat is 63 percent homozygous.¹³

The result of all of this genetic similarity is a population of animals with exceptionally high cub mortality rates, and with far more disease susceptibility than their fellow cats.¹⁴ And that, of course, was the situation facing cheetahs even before the human population explosion in Africa began to take its toll.

In the early 1900s, there were about 100,000 wild cheetahs stretched across Africa and Asia. Today there are about 7,000 left. And only two population groups offer any real hope of not inbreeding themselves out of existence¹⁵—one in southern Africa that has about 4,000 members, another in the Serengeti that has about 1,000. The other African clusters are small and shrinking, and there is likely no functional population left in Asia.

As you might suspect, poachers and traders are a big factor in this population freefall, but so are farmers, who kill the cheetahs to protect their livestock; when it comes to predator controversies, cheetahs are to Africa as wolves are to North America. Of nine free-roaming, collared cheetahs that were followed for a study published in 2017, four were shot by landowners.¹⁶ Roads are another huge hazard. When researchers tracked a population of cheetahs for two years in 2011 and 2012, they found that more than a quarter of verified deaths came as a result of being hit by cars or trucks.¹⁷

Put all of this together, and the result is a current rate of population decline some researchers believe to be 10 percent per year. If cheetah numbers continue to decline at that rate, half the world’s population could be gone in the next decade.

It is for these reasons that Zelealem Tefera Ashenafi, Born Free’s chief representative in Ethiopia, is circumspect about the chances of success for a release of the foundation’s rescued and rehabilitated cheetahs.

“Teaching them to hunt is a challenge, of course, but it is a challenge I believe we can overcome,” he told me. “The bigger problem is: Where do we take them? Where can we bring them where they will be safe, even relatively safe, from the threats that are destroying the cheetah populations everywhere?”

Still, he said, he wants to try. “Because,” he said, “what good is it to keep these cheetahs in our conservation center if they don’t actually help us contribute to conservation?”

He has been eyeing Awash National Park, about 100 miles to the east of Ensessakotteh, as a potential reintroduction area. “It’s close enough that we can vigilantly protect the cheetahs,” he said. “We can keep monitors there and give the cheetahs a soft release, with radio collars and food if, it turns out, they cannot provide for themselves.”

Still, Ashenafi lamented, the odds do not seem to be in the cheetah’s favor.

Yet in a century in which so many of their fellow vertebrates went extinct, and even as their very genomes conspired against them, cheetahs have managed to survive.

How? The answer may lie in the same lack of genetic diversity that also threatens their survival. That shallow selection of DNA may have essentially locked in the cats’ “speed genes,” which code for adaptations in muscle contraction, stress, and cardiopulmonary responses. There simply aren’t any “genetically slow” cheetahs who, when bred with the fast ones, would bring down the pack. Maintaining that speed over evolutionary time, even though they might not have needed it to catch much-slower prey, could have given cheetahs an evolutionary über-advantage that counteracted their genetic disadvantages.

“Some people say, ‘Well, now that this bottleneck has happened the cheetahs are totally screwed,’” O’Brien told me in 2017 while he was back in the United States during a break from his duties at St. Petersburg State University, where he is working to get more Russian scientists engaged in genomic analysis projects. “But I say that’s not necessarily true.”

A population bottleneck, O’Brien said, “is a little like a poker hand. Most of the time your cards are going to be mediocre, and sometimes you’re going to get a complete bust. But every bottleneck is a deck reshuffle, and sometimes you draw a card that makes your hand.”

Cheetahs were dealt an unusually good hand. “They retained a hell of a lot of good genes,” he said.

What we continue to learn, as we work to understand how cheetahs have managed to survive a shallow genetic pool, will undoubtedly help us address the challenges faced by other animals whose genetic diversity will suffer as their numbers shrink.

Of course, what we can learn will be badly diminished if cheetahs go extinct.

So the race is on.

WHY PRONGHORNS ARE ALWAYS RUNNING FROM GHOSTS

The pronghorn didn’t approach so much as appear before me. And in playing that moment back in my head, I still cannot figure out how we came to be standing face-to-face and just feet away from one another on that dusty bluff.

We stood there looking at one another for a moment. I tilted my head to the right. He dipped his down, then lifted it again and leaned back, exposing his muscular shoulders and the stark white triangle of fur on his chest. His coffee-brown horns were as long as the distance from my elbows to my fingertips, and rounded toward one another, nearly touching at the tips.

He was magnificent. The biggest pronghorn I’d ever seen—and I’ve seen quite a few. It’s hard to miss them in the Red Desert in southern Wyoming, the home of the largest migratory herd in North America.

I’m not sure how long it lasted. A minute perhaps, though it could have been five or ten. We took one another in. Squinting at each other in the late afternoon sun. For me, the whole world slowed down, and I wondered if that was his experience as well.

And then it happened. Something stirred in the sagebrush behind him—a jackrabbit maybe—and the pronghorn took off, bounding over scrub and rocks, left then right then hard left along a wash, leaning into the turns. In a matter of five or six seconds he was gone.

Pronghorns are known to reach a top speed of 55 miles per hour. That’s not quite as fast as a cheetah, but it’s not far off either. Pronghorns, though, can keep up the speeds that cheetahs typically reach for a lot longer. Cheetahs can run at 40 miles an hour for a few hundred meters; pronghorns can keep up those sorts of speeds for miles.¹⁸

How? Before answering that question, we need to have a talk about taxonomy.

Like many schoolchildren, my earliest mental images of the American West were largely informed by Brewster Higley’s poem “My Western Home,” which later became the song “Home on the Range.” But it turns out that Higley’s most famous lyric—“give me a home where the buffalo roam, where the deer and the antelope play”—did a bit of a disservice to our collective understanding of what animals actually live in the Great Plains. For there are no buffalo roaming the range in the United States, and there never have been. Like the African cape buffalo and the Asian water buffalo, the American bison is a member of the Bovidae family. But so are gazelles, sheep, and antelope—the latter of which is also not native to the United States. The “antelopes” we see on the plains are properly pronghorns.¹⁹

Culturally, these are semantic distinctions. There’s no good reason to stop referring to the five-cent pieces minted from 1913 to 1938 as “buffalo nickels.” And we don’t have to stop calling the largest island in the Great Salt Lake—where pioneer hunters reportedly found pronghorns so plentiful that it was hard to miss them—Antelope Island.

Scientifically, though, it’s important to understand that similarities in appearance between one life-form and another aren’t always reflective of a closely shared evolutionary history. So our biologist predecessors did us no favors when they, on occasion, not only made bad relational assumptions but enshrined those assumptions in taxonomic nomenclature, as they did in the case of the pronghorn, Antilocapra americana of the family Antilocapridae.

We live in a world in which comparative genomics is offering deep insights into the codes upon which our very existences are based. But hunting for shared DNA in two genomes is like searching for a few specific lines of text in an enormous library of books. And in such a search, it doesn’t help anyone if some of the books are mislabeled or have been put on the wrong shelves.²⁰

So we should be wary of assumptions made by our forebears, especially those that take on cultural gravitas, which can cloud our scientific perspective for generations. That was the case, as we know, with giraffes—which, it so happens, are far more closely related to the pronghorn than the antelope is.

To avoid predation, giraffes didn’t just evolve to be tall, but also to be very strong kickers—they can kill a lion with a single strike—and very fast runners. And pronghorns evolved the ability to run at high speeds for the same reason.

But if you only look at the predators that pronghorns have to contend with on the American prairie, you might wonder why they need to run so fast. Wolves and coyotes are quick, but they’re not nearly as fast as pronghorns. Even juvenile pronghorns can often outrun those predators.

So why do pronghorns need to drive 55?

The answers, some researchers believe, are Miracinonyx inexpectatus and Miracinonyx trumani, big cats belonging to a genus first identified by Edward Cope—of Cope’s Rule fame—that evolved alongside pronghorns for millions of years in North America, and that are sometimes called “false cheetahs.”²¹

The Miracinonyx cats, which were cougar-sized but cheetah-shaped and thus assumed to be really fast, died out about 11,000 years ago. But, the way zoologist John Byers sees it, their legacy lives on in the DNA of one of today’s best runners.

Pronghorns, Byers notes, “are truly Olympian runners in a world of notably less-than-Olympian predators.”²² And the reason they’re so overbuilt, he believes, is because they evolved as runners during a time in which North America was filled with predators like Miracinonyx.²³

Just about every animal is carrying some sort of evolutionary baggage it just doesn’t need anymore. Humans have tailbones, grow wisdom teeth, and get goose bumps, none of which are good for much these days. Given enough time, it’s reasonable to assume that we’d shake off these traits.

But traits born of a need for survival—not those that make life easier or a bit less dangerous, but those that acutely prevent death and extinction—seem to be a lot harder to get rid of when they’re not needed, or not needed as frequently. That might explain why, even though our day-to-day lives aren’t usually interrupted by attacks from saber-toothed cats or giant primate-eating eagles,²⁴ we can still rely on our sympathetic nervous system to give us a mega-dose of adrenaline and norepinephrine for surviving our much-less-common life-and-death situations.

And it means we get to see pronghorns run. Not just on the range, but on treadmills.

Yeah, treadmills.

That’s all thanks to a guy named Stan Lindstedt. With the evolutionary trigger for the pronghorn’s need for speed seemingly identified, the Northern Arizona University physiologist wanted to understand the biomechanics that allowed that evolution to happen.

Because pronghorns don’t really look like great runners. They look like furry sausages with spindly legs. Pronghorns aren’t shaped all that differently from goats, and no one would expect a goat to enjoy running.²⁵

Just to be sure, though, Lindstedt checked. Sure enough, goats don’t like treadmills. They’d only run when the researchers bribed them with a lot of food.

But when Lindstedt and his team put the pronghorns on the treadmills, they not only ran, but seemed to love doing so. “You’d open the door to the lab,” Lindstedt once told the New York Times, “and they’d run right in and jump on the treadmill.”²⁶

Unlike goats, Lindstedt found, pronghorns are perfectly built machines for transporting oxygen. Pronghorns have bigger tracheas with which to draw in oxygen. They have bigger lungs with which to absorb that oxygen. They have more hemoglobin with which to transport it to their muscles. And the cells in their muscles have a denser concentration of mitochondria with which to fuel contraction. Sure, pronghorns don’t look like speed machines, but looks can be deceiving.

Just ask the lowly mite.

WHY THE WORLD’S FASTEST RUNNER IS LIKE BATMAN

Anyone who has seen a cockroach scurry across the floor when the basement lights come on can attest to how fast these critters are. Although they have wings and can fly, they really don’t need to. They’re far slower in the air than they are on the ground.

For a long time, Guinness offered the American cockroach, Periplaneta americana,²⁷ the title of “fastest running insect.” Over time, though, researchers began to realize that—when it comes to hunting, and surviving the things that are hunting you—an animal’s speed relative to its body size is almost always more important than absolute speed. To determine a true fastest insect, an entomologist named Thomas Merrit gathered data from fellow insect researchers and crunched the numbers relative to each bug’s length. The resulting figures showed P. americana could move at a rate of 50 body lengths per second.

And that was fast. By comparison, after all, cheetahs can only run at about 16 body lengths per second. But in another insect, Merrit found a new champion. The Australian tiger beetle, Cicindela eburneola, could run at more than 170 body lengths per second. In relative terms, a six-foot man would have to run 720 miles per hour to be as fast.²⁸

But records are made to be broken. And nowhere is this more true than in nature, where wonders truly never cease.

In Claremont, California—not far from the lab where Daniel Martínez is maintaining a nearly immortal collection of hydra—a group of researchers led by an undergraduate named Samuel Rubin took note of a tiny mite, Paratarsotomus macropalpis, dashing across the sidewalks in the SoCal heat.

The mite was no secret. It had first been identified in 1916, and lived in the middle of one of the most highly populated metropolitan areas in the world. But no one had previously paid any scientific attention to it. A search of the ScienceDirect database through the early 2010s offers zero articles that so much as mentioned the little guy.

“They’re pretty easy to overlook,” said Jonathan Wright, Rubin’s former adviser at Pomona College and his co-author on the paper. “They’re tiny, about a millimeter long, and they move so quickly when they are running that, if you were not scrutinizing them carefully, you might just conclude they were a bit of blowing dust.”

They’re also darn hard to catch. Wright told me he’s thankful the mites like sidewalks and driveways, because trying to capture them in their natural sandy habitat generally results in in an aspirator jar full of dirt—and often no mites.

The team was able to get some video, though, of the mite darting about on the sidewalk. And when the researchers used that footage to trace a path behind the animal, then measured the distance it had traveled, they were floored.

At first Rubin thought he’d miscalculated. But when he ran the numbers again, it was clear: He’d helped discover the world’s fastest runner.

The mite was moving at up to 322 body lengths per second. The equivalent human speed would be something in the neighborhood of 1,300 miles per hour.²⁹ To put this into a bit of context: There are only about a dozen reported times in history that an airplane has gone faster than 1,300 miles per hour.

P. macropalpis wasn’t just leaping from one place to another. It was legitimately running—with a stride rate of 135 steps per second, the highest cycling of any weight-bearing muscle ever reported in any animal.³⁰ By way of comparison, human sprinters take about three steps per second. Even the famous “Jesus lizard,” the basilisk, which moves so fast it can walk on water, only takes about twenty steps per second.

By reinforcing the scientific theory of scaling—which suggests that the smaller organisms get, the less force they need to increase speed—the discovery of the mite’s amazing stride was soon being used to inform our understanding of the potential of nanomotors, organic engines capable of converting energy to movement at a molecular scale.³¹

P. macropalpis might also help teach us to create machines better adapted for acceleration, deceleration, and rapid turning. The tiny mite, after all, can stop in an instant, and can turn at speeds and angles that would rip other animals’ legs off.

To understand how it does that, Rubin and Wright slowed down the footage and blew it up big. When they did, they saw the mite had two strategies for turning, one for fast turns and one for really-stinking-fast turns.

The fast strategy is like an exaggerated version of how marching bands turn. To pivot in a column, the musicians on the inner part of the turn shorten their gait to the point of nearly marching in place, while those on the outside must lengthen their stride. The mite was doing the same thing—taking very short steps with the legs on the inside of the turn and longer steps with the legs on the outside.³²

The really-stinking-fast strategy is straight out of Tim Burton’s now-classic 1989 reboot of Batman, when the caped crusader deploys a grappling hook to help the Batmobile make a sharp turn during a car chase. Instead of a hook and rope, though, P. macropalpis uses its inside third leg, hooking into a chunk of the ground with its tarsus, and then accelerating out of the turn just like the Dark Knight, except smaller, creepier, and less bedeviled by abandonment issues.³³

Of course, the world’s most famous vigilante uses the Batmobile to pursue criminals, his particular form of prey. And that begs the question: What is P. macropalpis pursuing?

Nobody knows. But it’s almost certainly smaller, and could be even faster, than the mighty little mite.

So when it comes to relative speed, we might not have yet found the world’s fastest runner. But there are other members of the “fastest” club that are far more certain.

WHY ENGINEERS ARE TAKING A SECOND LOOK AT FALCONS

People long suspected the peregrine falcon was the fastest bird in the world—and the fastest animal of all, in terms of absolute speed. Its top velocity was long theoretical, though, because falcons operate in a vast, unpredictable, and very three-dimensional environment that makes a good radar-gun fix quite difficult. As recently as the late 1990s, we didn’t really know for sure how fast Falco peregrinus could fly.

That didn’t sit well with Ken Franklin. The professional pilot, master falconer, and amateur scientist knew birds had played an essential role in human flight. The Wright brothers extensively studied avian aeronautics before taking off at Kitty Hawk, and Orville Wright later wrote that “learning the secret of flight from a bird was a good deal like learning the secret of magic from a magician. After you know what to look for, you see things that you did not notice.” And yet, Franklin lamented, we didn’t even know what the fastest of all birds was capable of, because we weren’t looking.³⁴

So he decided to find out. And, since radar guns weren’t going to get the job done, he decided to take a different road. The high road, as it were.

Others had tried to calculate falcon speed by what was observable from the ground. But Franklin knew that peregrines often soar several miles in altitude—far past heights at which ground observations were possible. So, starting from a few thousand feet and moving progressively higher, Franklin and his falcon, whose name was Frightful, began a training regimen that culminated in both man and bird diving from a Cessna 172 at 17,000 feet.

Franklin wore a video camera. Frightful wore a half-ounce recording altimeter. Pursuing a lead-weighted lure that Franklin dropped once they were both diving together, Frightful tucked into a dive and reached a speed of 242 miles per hour.

At that speed, he was falling the length of a soccer field every second.

Franklin was hopeful the data he and his team gleaned from the Frightful experiments might help aerospace engineers better understand how to reduce drag and turbulence. And he worked hard to convince them to take a deeper look at the peregrine’s body shape, wing contour, and feather configuration during high-speed dives.

It turned out to be a tough sell. The writer Tom Harpole, who spent years following the exploits of Franklin and Frightful, thought for sure he’d found someone interested in understanding what airplane makers could learn from birds when he met Jim Crowder. Crowder was, after all, a senior technical fellow at Boeing whose specialty was studying airflow to improve the performance of planes. Crowder was also an amateur birder.

But while Crowder said he believed that “birds do all kinds of things that are unknown and potentially worth finding out about,” he also warned Harpole that the aviation industry saw itself as “a mature business” that had moved past birds as sources of knowledge for flight. Crowder lamented the conventional wisdom that, if there were aeronautical discoveries yet to be had, “someone would have found them by now.”

“Looking back, I do understand where they were coming from,” Franklin later told me. “I didn’t have a PhD. These people had spent their whole lives trying to quantify the mathematics of flight and, from their perspective, I was the new guy on the block who was throwing birds out of airplanes.”

Frightful passed away around 2012, and Franklin has retired from the skydiving game. He keeps pigeons these days instead of birds of prey. “Frightful and I made more than 200 jumps together,” he said. “We took it as far as we could.”

For more than a decade after Frightful set the animal air-speed record, falcon freefall got little more than a passing look from the aeronautics set. That finally changed, though, in the early 2010s.

That’s when a team of German scientists realized that maybe it wouldn’t be such a bad idea to at least take a look not only at how peregrines manage to go so fast, but also at how they withstand the high mechanical loads that push and pull against the birds’ 2-pound frames when they maneuver at such speeds. After all, when pulling out of an extreme dive while clutching a lure weighing nearly as much as she did, Frightful was confronted with more Gs than the limit for the US Air Force’s F-22 Raptor.³⁵

Building from observations taken during Frightful’s falls, the Germans trained a group of falcons to dive in front of a 200-foot dam. At that height the birds couldn’t reach maximum acceleration, but they did tuck into the same body and wing configuration Frightful had when falling much faster. Because the dam offered a high-contrast background, the researchers were able to reconstruct the bird’s exact flight path and body shape using multiple high-speed video cameras. With those images, the team built a life-sized model of one of its falcons, slathered it with oil paint, and put it in a wind tunnel. The streaks of paint showed how air moves around a falcon’s body during a fall.

And that’s when the German team noticed something interesting: regions of the model along the back and wings where paint had accumulated, indicating a separation of wind flow. When they went back to look at images of their birds, and honed in on that area, they noticed a series of small feathers that were popped up from the falcon’s body at the exact same locations the paint had pooled on the models. They hypothesized that the arrangement of feathers prevented the flow separation seen on the model.³⁶ Somehow, it seemed, the birds knew which areas of their wings were not moving air as efficiently, and had figured out a solution to the problem.

That finding excited Marco Rosti, then a doctoral student at the University of London. The young Italian aeronautical engineer was part of a team looking for novel ways to address the issue of stall, which happens when the direction of an aircraft wing and the direction of the oncoming airflow get too far out of parallel, causing significant airflow separation and loss of lift. The problem is as old as aviation; Otto Lilienthal, a pioneer in glider flight, died in 1896 after a crash caused by stall.³⁷ The century that followed has given us a tremendous number of innovations in aviation, but we haven’t “solved” stall.

Falcons seem to have solved it, though. So, building off what had been learned in the falcon experiments, Rosti and his fellow researchers devised a flap that could be hinged on the top side of a wing with a torsion spring. The self-activated flap was designed to pop up, just like the little feathers on a falcon’s wings, to disrupt the airflow separation.³⁸

Rosti said that the entire time he’d been studying aeronautics he was told the same sorts of things about animal flight that Ken Franklin had been in the wake of the Frightful flights. “What we heard was that perhaps some animals like insects were good to help us identify completely new ways of flying,” Rosti said, “but not for helping us improve the way we already fly.”

And yet interest in his team’s falcon-inspired solution to stall was red hot—and the enthusiasm was coming not just from airplane designers, but from the helicopter community as well, which also faces that age-old problem, albeit in different ways.

Rosti remains cautious. There are a lot of remaining hurdles, not the least of which is an aviation culture that is wedded to ideas about how airfoils are supposed to work, even when those ideas begin with the premise that, in a lot of situations, airfoils won’t work.

Ultimately, Rosti said, he accepts that his team’s design might not revolutionize air travel. But if it makes it a little less bumpy for some folks, he said, it will be worth the effort.

Perhaps more importantly, though, the bio-inspired design has proven people like Franklin right. We may be more than a century into our era of aviation, but falcons are millions of years into theirs. The idea that there’s nothing more to be learned from birds when it comes to human flight is pure hubris.

It’s just a story we’ve told ourselves. And stories aren’t always true.

HOW A WIDELY TOLD FISH TALE HELPED BLUEFIN TUNA CLAIM A SPOT IN THE RECORD BOOKS

As fish tales go, this one’s pretty good: From 1908 to 1935, sport fishermen would gather throughout the year at the Long Key Fishing Camp, an ocean anglers’ paradise off the tip of Florida made famous by the legendary American writer Zane Grey. And it was there, the story goes, that members of the club once observed a sailfish take out 300 feet of line in three seconds. If true, it meant that particular fish would have been swimming at 68 miles per hour. And that would make Istiophorus platypterus the fastest fish in the world.

It’s on the basis of this claim that the sailfish is widely credited as being “the world’s fastest fish.” The 68-mile-per-hour record has made its way onto thousands of websites, has been repeated by reputable publications like National Geographic and Field & Stream, as well as the National Oceanic and Atmospheric Administration,³⁹ and appears in quite a bit of scientific literature as well.⁴⁰

The primary source for the alleged observation, however, appears to have been lost to history—and it might not have come from Long Key at all.⁴¹

The funny thing is, once it was finally put to the test with an accelerometer-based series of measurements, it turned out that 68 might be quite a bit slower than the sailfish can actually go. Researchers at the University of Miami have concluded that I. platypterus is actually capable of hitting 78 miles per hour in a very short sprint.⁴²

But in improving the sailfish’s top speed, the Miami scientists might also have shortened its reign, because when the folks at the University of Massachusetts’ Large Pelagics Research Center—better known as “Tuna Lab”—learned about the new sailfish record, they got to thinking. If the purported sailfish record was so much slower than its actual potential speed, they wondered, what else was wrong?

The lab’s researchers had been watching Atlantic bluefin tuna, Thunnus thynnus, for years, and knew that particular fish, which can grow as heavy as 1,500 pounds, was exceptionally fast. Perhaps, they thought, it could reach instances of acceleration that pushed it past the 45-miles-per-hour mark typically referenced by sources that seemed little more credible than those that previously had been used for sailfish.

Working from the same playbook as their Miami colleagues, oceanographer Molly Lutcavage and her colleagues at Tuna Lab tagged a bunch of bluefins with miniature satellite tags. The tags are often used to track the movements of migrating animals, and are designed to pop off after a month, float to the surface, and send out a signal so that they can be recovered—usually by cooperating fishermen.

When a tag prematurely popped off an 800-pound bluefin after just a week, and the researchers got it back to Tuna Lab, they were stunned. The fish had been swimming so fast that the device had been torn into pieces.

How fast does a fish have to swim to shred a popup tag? The data download suggested the bluefin had reached a top speed of 144 miles per hour.

The tuna had been moving at more than twice the speed we’d long believed was the maximum for a fish.

Just like cheetahs, bluefin don’t keep their top speeds for long. The researchers estimated their record-setting tuna had maintained those super speeds for a matter of only a few seconds. But, not for nothing, those speeds were being reached in an environment that is roughly 800 times denser than air.

Remember how disinterested the aeronautical engineering community was in falcon flight? It’s early, yet, to know whether the nautical community will react with similar dispassion to the newly recognized masters of underwater speed, but it bears noting that there wasn’t much interest in understanding sailfish speed when it was widely assumed those creatures were the fastest things underwater. It wasn’t until 2013 that any meaningful examination of I. platypterus’s hydrodynamics was undertaken.⁴³

But bluefin might be a different story. For one thing, we’ve already got a better scientific starting point for their superlative claim to fame. For another, they’re tuna—and everybody knows tuna. Canned, sesame crusted and seared, or in a spicy sushi roll, we eat a lot of the stuff; it’s thus one of the most valuable fisheries in the world.⁴⁴

They’re also in trouble; Atlantic bluefin are listed as endangered by the International Union for the Conservation of Nature. The Center for Biological Diversity has petitioned the US federal government to also list T. thynnus under the Endangered Species Act, although so far to no avail.

At the intersection of economic value and population decline, there is often a flurry of research attention. That was true for bluefin even before it was suggested that they might be the fastest thing in the sea. Recent years, for instance, have brought studies on bluefin habitats in the Mediterranean Sea,⁴⁵ how bluefin DNA is different in different parts of the ocean,⁴⁶ and how tuna migrate and aggregate across the oceans.⁴⁷

And then there’s the US Navy’s GhostSwimmer, a robot designed to look, and swim, like a tuna. The autonomous underwater vehicle was designed as part of a secretive research and development operation called Silent Nemo. It was inspired in no small part by the RoboTuna project at the Massachusetts Institute of Technology, where engineers abandoned more than 200 years of conventional thinking about submarines to build an underwater vehicle designed to operate like a fish. The result was a submersible that was more maneuverable and used less energy than conventional unmanned submarines—and which, the Navy quickly recognized, could blend into the marine environment even better.

While the military hasn’t officially said so yet, it seems likely that GhostSwimmer could be a replacement for a frequently criticized Cold War–era operation, the furtive Navy Marine Mammal Program. The military organization uses dolphins and sea lions to hunt for mines, keep watch for underwater infiltrators, and recover lost equipment,⁴⁸ and also provides animals for translational research aimed at addressing human diseases and health concerns.⁴⁹ But that latter role doesn’t sit well with some animal welfare activists, who have pushed for the Navy’s program to be closed, reasoning that captive animal research should directly impact the conservation of the animals being studied.⁵⁰

One hang-up to swapping animals for robots: At least for the moment, GhostSwimmer isn’t as fast as dolphins and sea lions, nor does it have the endurance or dive capacity that the Navy’s trained marine mammals do. The robot fish can move up to 17 miles per hour in short durations or travel for longer periods at 3 miles per hour. A bottlenose dolphin can exceed 22 miles per hour and cruise for long periods at up to 7 miles per hour.⁵¹

But neither can come anywhere close to the burst speeds of a bluefin. And that could be important in a tactical setting. With that in mind, will the Navy seek to make its mechanical tuna even more tuna-like through a study of the natural adaptations that make bluefin so fast? Almost assuredly.

But will it succeed in making a mechanical animal that comes anywhere close to the 144-mile-an-hour burst speed capacity of the one Mother Nature designed? Probably not.

There’s absolutely no doubt that we can greatly improve our technology by looking to how animals have evolved in nature to solve challenges similar to the ones we face. But the more we do, the more clear it becomes:

Nature is way ahead of us.