DNA From a Shark Tooth Embedded in a Man's Foot for 25 Years Identifies the Culprit

Blacktip shark
Blacktip shark
Sahil Miyani, iStock / Getty Images Plus

It was unclear what species of shark attacked Jeff Weakley while he was surfing off Flagler Beach, Florida in 1994. Whether it was a tiger shark, bull shark, great white shark, or some other predator didn't matter at the time—his priority was swimming to safety before the shark could take another bite.

Twenty-five years later, the wound on Weakley's right foot has healed, and he's had plenty of time to wonder what exactly bit him on that beach trip. By analyzing a tooth fragment that was lodged in his foot for more than two decades, a team of scientists has finally given him an answer, the Ocala StarBanner reports.

Bits of shark tooth have come loose from Weakley's foot several times since he was attacked in 1994. The third time it happened, in fall 2018, he collected the shard and sent it to the Florida Program for Shark Research, a part of the Florida Museum of Natural History in Gainesville. He had just read an article about the program's work identifying shark species using the DNA from their teeth, and he suspected the team might be able to do the same with his tooth fragment.

His hunch was correct: The scientists analyzed the sample and confirmed that the shark that had bit Weakley a quarter-century earlier had been a blacktip shark (Carcharhinus limbatus). That finding was made possible by years of hard work. Over more than two decades, the program has amassed a database of shark DNA containing reference samples for roughly 70 percent of all known shark, skate, ray, and chimera species. Luck was also on their side: The researchers had feared that Weakley's immune system would have destroyed any DNA in the shark's tooth, but when it arrived at the lab, there was enough to make the identification.

Shark attacks are common in movies and TV, but much less so in real life. You're more likely to be struck by lighting or die from the flu than be the victim of a shark attack. When sharks do bite humans, it's often because they've mistaken them for a prey animal, and they'll usually let the victim go once they've realized their error. This is likely how Weakley escaped his shark attack with his foot mostly intact.

[h/t Ocala StarBanner]

7 Facts About Blood

Moussa81/iStock via Getty Images
Moussa81/iStock via Getty Images

Everyone knows that when you get cut, you bleed—a result of the constant movement of blood through our bodies. But do you know all of the functions the circulatory system actually performs? Here are some surprising facts about human blood—and a few cringe-worthy theories that preceded the modern scientific understanding of this vital fluid.

1. Doctors still use bloodletting and leeches to treat diseases.

Ancient peoples knew the circulatory system was important to overall health. That may be one reason for bloodletting, the practice of cutting people to “cure” everything from cancer to infections to mental illness. For the better part of two millennia, it persisted as one of the most common medical procedures.

Hippocrates believed that illness was caused by an imbalance of four “humors”—blood, phlegm, black bile, and yellow bile. For centuries, doctors believed balance could be restored by removing excess blood, often by bloodletting or leeches. It didn’t always go so well. George Washington, for example, died soon after his physician treated a sore throat with bloodletting and a series of other agonizing procedures.

By the mid-19th century, bloodletting was on its way out, but it hasn’t completely disappeared. Bloodletting is an effective treatment for some rare conditions like hemochromatosis, a hereditary condition causing your body to absorb too much iron.

Leeches have also made a comeback in medicine. We now know that leech saliva contains substances with anti-inflammatory, antibiotic, and anesthetic properties. It also contains hirudin, an enzyme that prevents clotting. It lets more oxygenated blood into the wound, reducing swelling and helping to rebuild tiny blood vessels so that it can heal faster. That’s why leeches are still sometimes used in treating certain circulatory diseases, arthritis, and skin grafting, and helps reattach fingers and toes. (Contrary to popular belief, even the blood-sucking variety of leech is not all that interested in human blood.)

2. Scientists didn't understand how blood circulation worked until the 17th century.

William Harvey, an English physician, is generally credited with discovering and demonstrating the mechanics of circulation, though his work developed out of the cumulative body of research on the subject over centuries.

The prevailing theory in Harvey’s time was that the lungs, not the heart, moved blood through the body. In part by dissecting living animals and studying their still-beating hearts, Harvey was able to describe how the heart pumped blood through the body and how blood returned to the heart. He also showed how valves in veins helped control the flow of blood through the body. Harvey was ridiculed by many of his contemporaries, but his theories were ultimately vindicated.

3. Blood types were discovered in the early 20th century.

Austrian physician Karl Landsteiner discovered different blood groups in 1901, after he noticed that blood mixed from people with different types would clot. His subsequent research classified types A, B and O. (Later research identified an additional type, AB). Blood types are differentiated by the kinds of antigens—molecules that provoke an immune system reaction—that attach to red blood cells.

People with Type A blood have only A antigens attached to their red cells but have B antigens in their plasma. In those with Type B blood, the location of the antigens is reversed. Type O blood has neither A nor B antigens on red cells, but both are present in the plasma. And finally, Type AB has both A and B antigens on red cells but neither in plasma. But wait, there’s more! When a third antigen, called the Rh factor, is present, the blood type is classified as positive. When Rh factor is absent, the blood type is negative.

Scientists still don’t understand why humans have different blood types, but knowing yours is important: Some people have life-threatening reactions if they receive a blood type during a transfusion that doesn’t “mix” with their own. Before researchers developed reliable ways to detect blood types, that tended to turn out badly for people receiving an incompatible human (or animal!) blood transfusion.

4. Blood makes up about 8 percent of our total body weight.

Adult bodies contain about 5 liters (5.3 quarts) of blood. An exception is pregnant women, whose bodies can produce about 50 percent more blood to nourish a fetus.)

Plasma, the liquid portion of blood, accounts for about 3 liters. It carries red and white blood cells and platelets, which deliver oxygen to our cells, fight disease, and repair damaged vessels. These cells are joined by electrolytes, antibodies, vitamins, proteins, and other nutrients required to maintain all the other cells in the body.

5. A healthy red blood cell lasts for roughly 120 days.

Red blood cells contain an important protein called hemoglobin that delivers oxygen to all the other cells in our bodies. It also carries carbon dioxide from those cells back to the lungs.

Red blood cells are produced in bone marrow, but not everyone produces healthy ones. People with sickle cell anemia, a hereditary condition, develop malformed red blood cells that get stuck in blood vessels. These blood cells last about 10 to 20 days, which leads to a chronic shortage of red blood cells, often causing to pain, infection, and organ damage.

6. Blood might play a role in treating Alzheimer's disease.

In 2014, research led by Stanford University scientists found that injecting the plasma of young mice into older mice improved memory and learning. Their findings follow years of experiments in which scientists surgically joined the circulatory systems of old and young mice to test whether young blood could reverse signs of aging. Those results showed rejuvenating effects of a particular blood protein on the organs of older mice.

The Stanford team’s findings that young blood had positive effects on mouse memory and learning sparked intense interest in whether it could eventually lead to new treatments for Alzheimer’s disease and other age-related conditions.

7. The sight of blood can make people faint.

For 3 to 4 percent of people, squeamishness associated with blood, injury, or invasive medical procedures like injections rises to the level of a true phobia called blood injury injection phobia (BII). And most sufferers share a common reaction: fainting.

Most phobias cause an increase in heart rate and blood pressure, and often muscle tension, shakes, and sweating: part of the body’s sympathetic nervous system’s “fight or flight” response. But sufferers of BII experience an added symptom. After initially increasing, their blood pressure and heart rate will abruptly drop.

This reaction is caused by the vagus nerve, which works to keep a steady heart rate, among other things. But the vagus nerve sometimes overdoes it, pushing blood pressure and heart rate too low. (You may have experienced this phenomenon if you’ve ever felt faint while hungry, dehydrated, startled, or standing up too fast.) For people with BII, the vasovagal response can happen at the mere sight or suggestion of blood, needles, or bodily injury, making even a routine medical or dental checkup cause for dread and embarrassment.

You Can Now Go Inside Chernobyl’s Reactor 4 Control Room

bionerd23, YouTube
bionerd23, YouTube

The eerie interior of Chernobyl’s Reactor 4 control room, the site of the devastating nuclear explosion in 1986, is now officially open to tourists—as long as they’re willing to don full hazmat suits before entering and undergo two radiology tests upon exiting.

Gizmodo reports that the structure, which emits 40,000 times more radiation than any natural environment, is encased in what's called the New Safe Confinement, a 32,000-ton structure that seals the space off from its surroundings. All things considered, it seems like a jolly jaunt to these ruins might be ill-advised—but radiology tests are par for the course when it comes to visiting the exclusion zone, and even tour guides have said that they don’t usually reach dangerous levels of radiation on an annual basis.

Though souvenir opportunists have made off with most of the plastic switches on the machinery, the control room still contains original diagrams and wiring; and, according to Ruptly, it’s also been covered with an adhesive substance that prevents dust from forming.

The newly public attraction is part of a concerted effort by the Ukrainian government to rebrand what has historically been considered an internationally shameful chapter of the country's past.

“We must give this territory of Chernobyl a new life,” Ukraine's president Volodymyr Zelensky said in July. “Chernobyl is a unique place on the planet where nature revives after a global man-made disaster, where there is a real 'ghost town.' We have to show this place to the world: scientists, ecologists, historians, tourists."

It’s also an attempt to capitalize upon the tourism boom born from HBO’s wildly successful miniseries Chernobyl, which prompted a 35 percent spike in travel to the exclusion zone earlier this year. Zelensky’s administration, in addition to declaring the zone an official tourist destination, has worked to renovate paths, establish safe entry points and guidelines for visitors, and abolish the photo ban.

Prefer to enjoy Chernobyl’s chilling atmosphere without all the radioactivity? Check out these creepy photos from the comfort of your own couch.

[h/t Gizmodo]

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