9 Surprising Facts About Sharks


Far from mindless killing machines, as they’re so often portrayed, these members of the class Chondrichthyes, or cartilaginous fish, are fascinating age-old survivors with a critical role in the ocean ecosystem.

1. The Shark Immune System Could Help Humans.

Sharks are among the oldest animals with a modern immune system, one similar to ours but with a sophisticated twist that may prove beneficial to humans. Shark blood contains large quantities of urea, which protects them from dehydrating in their salt water habitat. Urea can also destabilize sensitive protein molecules such as antibodies, though, and similar levels would destroy those in humans. Sharks have an additional salt bridge between structurally important amino acid chains and a particularly large non-polar nucleus of the Immunoglobulin fold in their antibodies—a complicated way of saying they have special adaptations to handle all that urea. Researchers now have integrated these adaptations into human antibodies, resulting in increased stability that could lead to improved therapy and diagnosis for human diseases.

2. Great Whites Live Much Longer than We Previously Thought.

Estimating the age of a great white shark presents a challenge—and no, getting close enough to one to ask isn’t the problem. Scientists determine the age of bony fish by analyzing mineralized tissues—ear bones, vertebrae, and fin rays—that have annual rings much the same as trees. Sharks have skeletons made of cartilage, not bone, except for their vertebrae. And while vertebrae do contain layers of tissue laid down sequentially over time, the bands can be less distinct and don't necessarily equate to annual growth. Using this method had previously yielded top ages for great whites of 23 years. When researchers used radiocarbon to analyze collagen in the vertebrae, they estimated the largest male was 73 years old, making great whites among the longest-lived cartilaginous fishes. Guess they need that unlimited supply of teeth.

3. Some sharks return to their birthplace to reproduce.

Sea turtles are famous for returning to the beaches where they hatched to lay their own eggs, many miles and decades later. Scientists call that natal philopatry and long-term fidelity to parturition sites. Turns out, some sharks have that, too.

A 19-year study that began in 1995 and involved the capture, tagging, and release of more than 2000 baby sharks revealed that female lemon sharks returned to where they were born to give birth, up to 15 years later. The discovery means that preserving local nursery habitats could protect future generations of sharks.

4. Oils stored in the liver fuel a great white’s long migration.

Great white sharks make non-stop trips of more than 2500 miles across the Pacific Ocean, crossing large swaths of open water with little if anything for them to eat. A study reveals that fuel for the journey comes from fat stored in the sharks’ livers, which account for up to a quarter of their body weight. It’s an approach similar to how hibernating bears bulk up and migrating whales pack on the blubber. Oils stored in the liver also provide the sharks with increased buoyancy.

Scientists used data records from white sharks in the eastern Pacific, equipped with electronic tags that record location, depth, and water temperature, to identify periods of drift diving—when marine animals descend passively and allow momentum to carry them forward like underwater hang gliders. The researchers estimated the amount of oil in an animal’s liver by measuring the rate at which it sank during drift dives; less oil to provide buoyancy meant a quicker descent while more oil equaled a slower one. Consistent decreases in buoyancy during migration indicated gradual but steady depletion of oil in the liver, meaning the sharks depended on that stored energy for their journey.

5. Shark embryos can detect danger.

Shark embryos inside an external egg case can detect the presence of predators and freeze, Bambi-style, to avoid being detected themselves. Adult sharks detect electric fields emitted by potential prey, and their embryos employ similar receptors to detect potential predators. When researchers created electric fields mimicking a predator, brown-banded bamboo shark embryos grew more still by reducing respiratory gill movements. Knowing about this behavior could help humans develop more effective ways of repelling grown-up sharks.

6. Humans and sharks share a common ancestor and similar genes.

Jawed vertebrates on earth—including sharks and humans—have a common ancestor, most likely Acanthodes bronni. Using more than 100 body characteristics, researchers compared resemblance among the earliest jawed fishes and found that Acanthodians as a whole clustered with ancient sharks. Perhaps it won’t surprise you that our relationship didn’t last long; the descendants of this shark-like fish from the Paleozoic era split more than 420 million years ago into early sharks and the first bony fishes, with humans eventually evolving from the latter. We remain connected, though, as recent large-scale analysis of the genes of great white sharks revealed that the proportion of its genes associated with metabolism and its heart RNA molecules were more similar to those of humans than of zebrafish, part of the bony fish line.

7. The shark family is large and diverse.

There are nearly 500 species of sharks. This large extended family includes the 6 inch dwarf lantern shark and the 40 foot whale shark, the round and flattened angel shark and the gape-mouthed basking shark. There are families of gulper sharks, lantern sharks, sleeper sharks and dogfish sharks; angel, bullhead, and carpet sharks. There are even zebra, crocodile, mackerel, hound, weasel, and cat sharks (something of a theme there). The family includes rays and skates as well. And as-yet undiscovered species likely lurk in the abyss, where as recently as 1976 we discovered Megamouth, a deep-water shark reaching lengths of 16 feet with a short snout and large mouth sporting 50 rows of teeth. And you thought your relatives were strange.

8. Shark skin reduces drag—and provides thrust.

Sharks are legendary for their efficiency at moving through the water, thanks to a streamlined body and tiny denticles, or tooth-like scales, on their skin that reduce drag. Sharkskin has inspired the design of suits worn by human swimmers and other marvels of engineering. It turns out that as a shark’s body flexes when it swims, the denticles alter the structure of water flow—technically they ‘promote enhanced leading-edge suction’—which may actually provide thrust in addition to reducing drag. Advantage: shark.

9. Sharks and human hunter-gatherers share the same foraging pattern.

Sharks, bees, and many other animals follow a pattern known as the Levy walk when they forage. This pattern of movement is similar to the mathematical ratio phi, which has been found to describe proportions in plants and animals throughout nature. A recent study confirmed that hunter-gatherer tribes of humans also follow the pattern, showing yet again that we have more in common with sharks than you might think.

BONUS RAY FACT: Devil Rays dive deeper than a mile.

Devil rays grow up to 13 feet across, travel across large areas of the ocean, and are often spotted in warm, shallow waters. But scientists recently discovered that these rays dive deeper than a mile. They tracked 15 animals in the central North Atlantic using pop-up satellite archival transmitting tags, which stay on the animals for up to 9 months, recording water temperature, depth, and light levels. The tags eventually pop off, float to the surface, and beam their data via satellite to waiting computers on shore. These 15 tags revealed that their bearers routinely descended almost 1.24 miles deep, traveling at speeds up to 13.4 miles per hour, and remaining there for two or three hours. That’s a hell of a dive.

All images courtesy of iStock.

Scientific Reports, Fernando Ramirez Rozzi
Stones, Bones, and Wrecks
Humans Might Have Practiced Brain Surgery on Cows 5000 Years Ago
Scientific Reports, Fernando Ramirez Rozzi
Scientific Reports, Fernando Ramirez Rozzi

In the 1970s, archaeologists discovered a site in France containing hundreds of cow skeletons dating back 5000 to 5400 years. The sheer number wasn't surprising—human agriculture in that part of the world was booming by 3000 BCE. What perplexed scientists was something uncovered there a few decades later: a cow skull bearing a thoughtfully drilled hole. Now, a team of researchers has released evidence that suggests the hole is an early example of animal brain surgery.

Fernando Ramírez Rozzi, a paleontologist with the French National Center for Scientific Research, and Alain Froment, an anthropologist at the Museum of Mankind in Paris, published their findings in the journal Nature Scientific Reports. After comparing the opening to the holes chiseled into the skulls of humans from the same era, they found the bones bore some striking similarities. They didn't show any signs of fracturing from blunt force trauma; rather, the hole in the cow skull, like those in the human skulls, seemed to have been carved out carefully using a tool made for exactly that purpose. That suggests that the hole is evidence of the earliest known veterinary surgery performed by humans.

Trepanation, or the practice of boring holes into human skulls, is one of the oldest forms of surgery. Experts are still unsure why ancient humans did this, but the level of care that went into the procedures suggests that the surgery was likely used to treat sick patients while they were still alive. Why a person would perform this same surgery on a cow, however, is harder to explain.

The authors present a few theories, the first being that these ancient brain surgeons were treating a sick cow the same way they might treat a sick human. If a cow was suffering from a neural disease like epilepsy, perhaps they though that cutting a hole in its head would relieve whatever was agitating the brain. The cow would have needed to be pretty special to warrant such an effort when there were hundreds of healthy cows living on the same plot of land, as evidenced by the skeletons it was found with.

Another possible explanation was that whoever operated on the cow did so as practice to prepare them for drilling into the heads of live humans one day. "Cranial surgery requires great manual dexterity and a complete knowledge of the anatomy of the brain and vessel distribution," the authors write in the study. "It is possible that the mastery of techniques in cranial surgery shown in the Mesolithic and Neolithic periods was acquired through experimentation on animals."

Either way, the bovine patient didn't live to see the results of the procedure: The bone around the hole hadn't healed at all, which suggests the cow either died during surgery or wasn't alive to begin with.

15 Incredible Facts About Pigeons

Though they're often described as "rats with wings" (a phrase popularized by the movie Stardust Memories), pigeons are actually pretty cool. From homing instincts to misleading rump feathers, here are 15 things you might not know about these avian adventurers.


The common city pigeon (Columba livia), also known as the rock pigeon, might be the first bird humankind ever domesticated. You can see them in art dating back as far as 4500 BCE in modern Iraq, and they've been a valuable source of food for thousands of years.


Pigeon-breeding was a common hobby in Victorian England for everyone from well-off businessmen to average Joes, leading to some fantastically weird birds. Few hobbyists had more enthusiasm for the breeding process than Charles Darwin, who owned a diverse flock, joined London pigeon clubs, and hobnobbed with famous breeders. Darwin's passion for the birds influenced his 1868 book The Variation of Animals and Plants Under Domestication, which has not one but two chapters about pigeons (dogs and cats share a single chapter).

Nikola Tesla was another great mind who enjoyed pigeons. He used to care for injured wild pigeons in his New York City hotel room. Hands down, Tesla's favorite was a white female—about whom he once said, "I loved that pigeon, I loved her as a man loves a woman and she loved me. When she was ill, I knew and understood; she came to my room and I stayed beside her for days. I nursed her back to health. That pigeon was the joy of my life. If she needed me, nothing else mattered. As long as I had her, there was a purpose in my life." Reportedly, he was inconsolable after she died.


In a 2017 Current Biology study, researchers showed captive pigeons a series of digital lines on a computer screen for either two or eight seconds. Some lines were short, measuring about 2.3 inches across; others were four times longer. The pigeons were trained to evaluate either the length of the line or how long it was displayed. They found that the more time a line was displayed, the longer in length the pigeon judged it to be. The reverse was true too: If the pigeons encountered a longer line, they thought it existed in time for a greater duration. Pigeons, the scientists concluded, understand the concepts of both time and space; the researchers noted "similar results have been found with humans and other primates."

It's thought that humans process those concepts with a brain region called the parietal cortex; pigeon brains lack that cortex, so they must have a different way of judging space and time.


A pigeon flying in front of trees.

The birds can do this even if they've been transported in isolation—with no visual, olfactory, or magnetic clues—while scientists rotate their cages so they don't know what direction they're traveling in. How they do this is a mystery, but people have been exploiting the pigeon's navigational skills since at least 3000 BCE, when ancient peoples would set caged pigeons free and follow them to nearby land.

Their navigational skills also make pigeons great long-distance messengers. Sports fans in ancient Greece are said to have used trained pigeons to carry the results of the Ancient Olympics. Further east, Genghis Khan stayed in touch with his allies and enemies alike through a pigeon-based postal network.


Pigeons' homing talents continued to shape history during the 20th century. In both World Wars, rival nations had huge flocks of pigeon messengers. (America alone had 200,000 at its disposal in WWII.) By delivering critical updates, the avians saved thousands of human lives. One racing bird named Cher Ami completed a mission that led to the rescue of 194 stranded U.S. soldiers on October 4, 1918.


In 1964, scientists in Holmdel, New Jersey, heard hissing noises from their antenna that would later prove to be signals from the Big Bang. But when they first heard the sound, they thought it might be, among other things, the poop of two pigeons that were living in the antenna. "We took the pigeons, put them in a box, and mailed them as far away as we could in the company mail to a guy who fancied pigeons," one of the scientists later recalled. "He looked at them and said these are junk pigeons and let them go and before long they were right back." But the scientists were able to clean out the antenna and determine that they had not been the cause of the noise. The trap used to catch the birds (before they had to later be, uh, permanently removed) is on view at the Smithsonian Air & Space Museum.


Japanese psychologist Shigeru Watanabe and two colleagues earned an Ig Nobel Prize in 1995 for training pigeons, in a lab setting, to recognize the paintings of Claude Monet and Pablo Picasso and to distinguish between the painters. The pigeons were even able to use their knowledge of impressionism and cubism to identify paintings of other artists in those movements. Later, Watanabe taught other pigeons to distinguish watercolor images from pastels. And in a 2009 experiment, captive pigeons he'd borrowed were shown almost two dozen paintings made by students at a Tokyo elementary school, and were taught which ones were considered "good" and which ones were considered "bad." He then presented them with 10 new paintings and the avian critics managed to correctly guess which ones had earned bad grades from the school's teacher and a panel of adults. Watanabe's findings indicate that wild pigeons naturally categorize things on the basis of color, texture, and general appearance.


In a 2016 study, scientists showed that pigeons can differentiate between strings of letters and actual words. Four of the birds built up a vocabulary of between 26 and 58 written English words, and though the birds couldn't actually read them, they could identify visual patterns and therefore tell them apart. The birds could even identify words they hadn't seen before.


A white pigeon with curly feathers and fluffy feet.

A few pigeon breeds have fuzzy legs—which hobbyists call "muffs"—rather than scaly ones. According to a 2016 study, the DNA of these fluffy-footed pigeons leads their hind legs to take on some forelimb characteristics, making muffed pigeon legs look distinctly wing-like; they're also big-boned. Not only do they have feathers, but the hindlimbs are somewhat big-boned, too. According to biologist Mike Shapiro, who led the study, "pigeons' fancy feathered feet are partially wings."


In a life-or-death situation, a pigeon's survival could depend upon its color pattern: Research has shown that wild falcons rarely go after pigeons that have a white patch of feathers just above the tail, and when the predators do target these birds, the attacks are rarely successful.

To figure out why this is, Ph.D. student Alberto Palleroni and a team tagged 5235 pigeons in the vicinity of Davis, California. Then, they monitored 1485 falcon-on-pigeon attacks over a seven-year span. The researchers found that although white-rumped pigeons comprised 20 to 25 percent of the area's pigeon population, they represented less than 2 percent of all the observed pigeons that were killed by falcons; the vast majority of the victims had blue rumps. Palleroni and his team rounded up 756 white- and blue-rumped pigeons and swapped their rump feathers by clipping and pasting white feathers on blue rumps, and vice versa. The falcons had a much easier time spotting and catching the newly blue-rumped pigeons, while the pigeons that received the white feathers saw predation rates plummet.

Close observation revealed that the white patches distract birds of prey. In the wild, falcons dive-bomb other winged animals from above at high speeds. Some pigeons respond by rolling away in midair, and on a spiraling bird, white rump feathers can be eye-catching, which means that a patch of them may divert a hungry raptor's focus long enough to make the carnivore miscalculate and zip right past its intended victim.


Two blue and green Nicobar pigeons.

Though most of this list focuses on the rock pigeon, there are 308 living species of pigeons and doves. Together, they make up an order of birds known as the columbiformes. The extinct dodo belonged to this group as well.

Flightless and (somewhat) docile, dodos once inhabited Mauritius, an island near Madagascar. The species had no natural predators, but when human sailors arrived with rats, dogs, cats, and pigs, it began to die out, and before the 17th century came to a close, the dodo had vanished altogether. DNA testing has confirmed that pigeons are closely related to the dodo, and the vibrant Nicobar pigeon (above) is its nearest genetic relative. A multi-colored bird with iridescent feathers, this near-threatened creature is found on small islands in the South Pacific and off Asia. Unlike the dodo, it can fly.


Wild/feral rock pigeons reside in all 50 states, which makes it easy to forget that they're invasive birds. Originally native to Eurasia and northern Africa, the species was (most likely) introduced to North America by French settlers in 1606. At the time, a different kind of columbiform—this one indigenous—was already thriving there: the passenger pigeon (Ectopistes migratorius). As many as 5 billion of them were living in America when England, Spain, and France first started colonizing, and they may have once represented anywhere from 25 to 40 percent of the total U.S. bird population. But by the early 20th century, they had become a rare sight, thanks to overhunting, habitat loss, and a possible genetic diversity issue. The last known passenger pigeon—a captive female named Martha—died on September 1, 1914.


According to one study, they're more efficient multitaskers than people are. Scientists at Ruhr-Universitat Bochum put together a test group of 15 humans and 12 pigeons and trained all of them to complete two simple jobs (like pressing a keyboard once a light bulb came on). They were also put in situations wherein they'd need to stop working on one job and switch over to another. In some trials, the participants had to make the change immediately. During these test runs, humans and pigeons switched between jobs at the same speed.

But in other trials, the test subjects were allowed to complete one assignment and then had to wait 300 milliseconds before moving on to the next job. Interestingly, in these runs, the pigeons were quicker to get started on that second task after the period ended. In the avian brain, nerve cells are more densely packed, which might enable our feathered friends to process information faster than we can under the right circumstances.


Only mammals produce genuine milk, but pigeons and doves (along with some other species of birds) feed their young with something similar—a whitish liquid filled with nutrients, fats, antioxidants, and healthy proteins called "crop milk." Both male and female pigeons create the milk in the crop, a section of the esophagus designed to store food temporarily. As is the case with mammal milk, the creation of crop milk is regulated by the hormone prolactin. Newly-hatched pigeons drink crop milk until they're weaned off it after four weeks or so. (And if you've ever asked yourself, "Where are all the baby pigeons?" we have the answer for you right here.)


We've already established that pigeons are excellent at differentiating between artists and words, but a 2015 study revealed they can also distinguish between malignant and benign growths in the right conditions. Researchers at University of California Davis Medical Center put 16 pigeons in a room with magnified biopsies of potential breast cancers. If the pigeons correctly identified them as either benign or malignant, they got a treat, According to Scientific American.

"Once trained, the pigeons' average diagnostic accuracy reached an impressive 85 percent. But when a "flock sourcing" approach was taken, in which the most common answer among all subjects was used, group accuracy climbed to a staggering 99 percent, or what would be expected from a pathologist. The pigeons were also able to apply their knowledge to novel images, showing the findings weren't simply a result of rote memorization."

Mammograms proved to be more of a challenge, however; the birds could memorize signs of cancer in the images they were trained on but could not identify the signs in new images.

No matter how impressive their results, "I don't anticipate that pigeons, no matter how good they become at pathology or radiology, will be playing a role in actual patient care—certainly for the foreseeable future," study co-author Richard M. Levenson told Scientific American. "There are just too many regulatory barriers—at least in the West."


More from mental floss studios