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10 Questions Still Baffling Scientists

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Science has done a terrific job of answering some of the world’s most difficult questions, but certain mysteries still elude researchers. How does gravity work? Can your pet fish really predict an earthquake? Why do we yawn so much? Here’s what we don’t know and how close we are to figuring it out.

1. Why Do We Yawn?

Theories about why we yawn are as common as grumpy toddlers at nap time, but two explanations seem plausible after experimental tests. One is that yawns help cool the brain and optimize its performance. Psychologists at the State University of New York at Albany say it explains why we yawn when we’re drowsy: Like the fan in a computer, the yawn kicks in when our performance starts lagging.

But if yawns are our brains’ way of kick-starting their efficiency, why is yawning contagious? The brain-cooling camp suggests that it’s a way to maintain group vigilance and safety. When a member of a pack yawns, signaling that he is not functioning at his best, the whole group may need to yawn for a collective cognitive boost.

That’s not the only theory floating around, though. Another explanation contends that contagious yawning builds and maintains empathy between yawners. A sympathetic yawn signals an appreciation and understanding of someone else’s condition and subconsciously says, “Me too, buddy.” So which story is the accurate one? Scientists aren’t ready to declare a winner yet—they need a little time to sleep on it.

2. Why Do People Spontaneously Combust?

Here’s what we know: Humans really do spontaneously combust. One of the first people recorded to have gone up in smoke is a poor Italian knight who burst into flames after drinking strong wine in the mid–17th century. The cause of the mysterious fireworks befuddles scientists, but they’re certain that each instance is less spontaneous than it seems. Over centuries, 120 cases of spontaneous human combustion have been reported, but because most of the cases involve smokers, a common hypothesis is that an outside flame is involved. The theory is that a cigarette scorches the skin and breaks it deep enough to force body fat to seep rapidly from the wound into burning clothing; together they act like candle wax and a wick.

It’s far more probable than the competing idea—that methane gases build up in the intestines and are sparked from inside the body by a mix of enzymes. But there’s a problem with testing both theories: Researchers can’t just walk around setting people on fire. They may have found a substitute that will answer the question, though. Pig tissue combusts in a way that’s consistent with the “wick effect,” and samples are far easier to obtain. Who knew bacon would help solve the mystery of one of Spinal Tap’s drummers?

3. Why Do Placebos Work?

When a new drug enters clinical trials, researchers need a control group against which to compare its effects. Members of this group are given what they’re told is the drug but is actually a pill containing no active ingredients, a placebo. Frequently, though, the control subjects feel the drug’s effects. Or at least they say they do. What actually happens to placebo poppers is still unsettled. Some studies have found objectively measured effects that are in line with a real drug’s results. Others have found that the benefits are only subjective; patients said they felt better after taking the placebo, regardless of their actual improvement. This mixed bag of evidence could support any number of explanations. There could be an actual physiological response, Pavlovian conditioning (a patient expects to feel better after medicating), positive feelings from patient-doctor interactions, an unconscious desire to “do well” in a clinical trial, or even a natural improvement in symptoms.

Whatever the cause, pharmaceutical companies are keen to figure out the placebo effect given its potential to throw clinical trials into disarray. Real drugs often can’t compete against the effects of fakers, and about half get scrapped in late-stage trials. For the researchers who’ve spent nearly 10 years trying to bring their drugs to market, that’s a bitter pill to swallow.

4. What Was Life’s Last Universal Common Ancestor?

A whale and a bacterium or an octopus and an orchid don’t seem to have much in common, but deep down they’re all the same. Research reveals that most of life’s tiniest components, like proteins and nucleic acids, are nearly universal. The genetic code is written in the same way across all organisms. A small core of genome sequences is also similar across major branches of life’s family tree. All this suggests that every living thing made of cells can trace its lineage back to one source, a universal common ancestor.

In theory, this idea makes a lot of sense. Getting this ancestor to show up for a paternity test is tougher. Scientists estimate that the last universal common ancestor (LUCA) split into microbes and later eukaryotes (animals, plants, and the like) around 2.9 billion years ago. The fossil record from that era is scant, and by now, the genes that have traveled down the family tree have been lost, swapped, or shuffled around.

But some features of proteins and nucleic acids encoded by these genes—such as their three-dimensional structure—have been preserved throughout time. A survey of these molecular traits offers a glimpse at what the last universal common ancestor might have looked like. Researchers have found that tiny organelles (specialized subparts of cells) as well as their associated enzymes are shared by all major branches of life, meaning that they must have been present in the last universal common ancestor. This and other evidence suggests that the LUCA was as complex as a modern cell—which doesn’t make our forebear all that visually impressive. But on the plus side, until scientists get to the bottom of this question, we can all save money on Father’s Day cards for the granddaddy of all life on Earth.

5. How Does Memory Work?

For a long time, neuroscientists thought a memory was stored in a scattered group of neurons in either the hippocampus or in the neocortex. Last year, researchers at MIT proved that theory for the first time by causing mice to remember or forget an event by activating or deactivating the associated neurons.

It’s an essential piece to the puzzle, but to recall a memory on its own, the brain has to activate the correct assortment of neurons. And how exactly the brain pulls off that trick isn’t fully understood. Studies on rodents and brain imaging in people suggests that some of the same neurons that the original experience affected are involved. In other words, remembering something may not just be a matter of grabbing it from its storage space but re-forming the memory each time it’s pulled out.

6. Can Animals Really Predict Earthquakes?

The idea that our furry and feathered friends could warn us about impending doom is a nice one, but it’s been hard for scientists to prove. Pet owners have noted how their animals acted funny just before an earthquake since the days of ancient Greece. There’s no shortage of reports, but almost every one is anecdotal, based on opinions of what’s “normal” and “funny” for an animal. And the stories are generally reported long after the fact.

It’s not out of the question that animals may sense and react to some environmental change that we don’t notice—anything from seismic waves to changes in electric or magnetic fields. However, it’s not clear that earthquakes even produce such precursors. Plus, whatever the proposed cause, it’s nearly impossible to test. If we can’t predict earthquakes, we don’t know when to observe animals, and it’s even more difficult for researchers trying to reproduce the experiment later. The few “lucky” cases where quakes happened during animal experiments provide conflicting evidence. If you’re going to rely on a cat for earthquake advice, consult one with a degree in seismology.

7. How Do Organs Know When to Stop Growing?

Every mammal starts out as a single cell before growing into trillions of them. Usually, there’s tight control over the number and size of cells, tissue, and organs, but sometimes things go very wrong, resulting in anything from cancer to a leg that’s larger than its partner. So what’s sending the “stop growing” signal?

Four proteins that make up the core of what’s known as the Salvador-Warts-Hippo signaling pathway appear to help regulate growth for a number of organs. Shutoff signals sent down the pathway deactivate the protein that promotes growth, but that’s where scientists’ knowledge stops. Where these signals originate and which other elements are affecting SWH is unknown. Scientists continue to learn how to manipulate the pathway, discovering new triggers and working their way to the source, but there are still a lot of mysteries—including how we may be able to “turn off” cancer.

8. Are There Human Pheromones?

Can you actually smell someone’s fear? Or sniff out a rat? Plenty of animals communicate with chemical signals called pheromones, but whether humans are part of that club is a contentious issue. There’s some evidence of people making behavioral and physical changes in response to chemosignals, but scientists haven’t been able to figure out which chemicals trigger these responses. And despite what the labels on pheromone-infused colognes and hair gels will tell you, no compound has been identified as a human pheromone or linked to a specific response.

Moreover, if people are giving off pheromones, scientists aren’t sure how others are detecting them. Many mammals and reptiles have what’s known as a vomeronasal organ that detects pheromones. While some human noses contain the tiny organ, it may not be functional; sensory neurons have little or no connection with the nervous system. So for now, the answer to this question remains “maybe.” And that uncertainty truly stinks.

9. What’s the Deal With Gravity?

Of the four fundamental forces of nature, gravity is the runt of the litter. It holds the universe together, but it’s weaker than its three siblings: electromagnetism, weak nuclear forces, and strong nuclear forces. How much punier is it? The next step up, weak nuclear, is 10^26 (100,000,000,000,000,000,000, 000,000) times stronger. Gravity’s relatively feeble pull makes it hard to demonstrate with small objects in the lab.

Gravity doesn’t play well with the other forces either. Try as they might, scientists can’t use quantum theory and general relativity to explain gravity on small scales. And this incompatibility leaves us short of physicists’ grandest goal: a unified theory of everything.

Worse still, scientists can’t even figure out what gravity is made of. The other fundamental forces are all associated with particles that help carry them, but no one’s been able to detect the gravitational particle—the hypothetical graviton—even with the most super of supercolliders! And while some scientists are frustrated by its elusive nature, others know it’s just gravity’s way—the force has a reputation for bringing us down.

10. How Many Species Are There?

Taxonomists have been finding, naming, and describing species in an organized manner for more than 200 years, and they’re probably nowhere close to being finished. It’s not that they’re slacking off on the job either. In the last decade alone, scientists have reported more than 16,000 new species per year; in total, they’ve cataloged 1.2 million. It’s anybody’s guess how many are left undiscovered, though. Going out and finding every single species would take the 300,000 working taxonomists a lifetime, so they have to make educated guesses.

Making these kinds of extrapolations presents serious logistical hurdles. Biodiversity hotspots often fall in developing countries, which suffer from a shortage of taxonomists. Furthermore, up to 80 percent of the planet’s life may be hiding out in hard-to-reach places under the sea.

Given these troubles, it’s no wonder there’s a wide variance in expert guesses of how many species are left undiscovered. The most recent ballpark figures place the number between five and 15 million species, which makes the odds of someone discovering a unicorn just slightly better than we’d even dared to dream.

This story originally appeared in mental_floss magazine.

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25 Royals in the Line of Succession to the British Throne
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Dan Kitwood, Getty Images

Between the Duke and Duchess of Cambridge welcoming their third child on April 23, 2018 and Prince Harry's upcoming marriage to Suits star Meghan Markle in May, the line of succession to the British throne has become a topic of interest all over the world. And the truth is, it’s complicated. Though Queen Elizabeth II, who turned 92 years old on April 21, shows no signs of slowing down, here are the royals who could one day take her place on the throne—in one very specific order.

1. PRINCE CHARLES

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As a direct result of his mother being the world's longest-reigning monarch, Prince Charles—the eldest child of Queen Elizabeth II and Prince Philip—is the longest serving heir to the throne; he became heir apparent in 1952, when his mother ascended to the throne.

2. PRINCE WILLIAM

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At 35 years old, odds are good that Prince William, Duke of Cambridge—the eldest son of Prince Charles and the late Princess Diana—will ascend to the throne at some point in his lifetime.

3. PRINCE GEORGE 

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On July 22, 2013, Prince William and Catherine, Duchess of Cambridge welcomed their first child, Prince George of Cambridge, who jumped the line to step ahead of his uncle, Prince Harry, to become third in the line of succession.

4. PRINCESS CHARLOTTE 

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On May 2, 2015, William and Catherine added another member to their growing brood: a daughter, Princess Charlotte of Cambridge. Though her parents just welcomed a bouncing baby boy, she will maintain the fourth-in-line position because of the Succession to the Crown Act 2013, which went into effect just a few weeks before her arrival, and removed a long-held rule which stated that any male sibling (regardless of birth order) would automatically move ahead of her.

5. PRINCE OF CAMBRIDGE

 Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge depart the Lindo Wing with their newborn son at St Mary's Hospital on April 23, 2018 in London, England
Chris Jackson, Getty Images

On April 23, 2018, the Duke and Duchess of Cambridge welcomed their third child—a son, whose name has yet to be announced, but who has already pushed his uncle, Prince Harry, out of the fifth position in line to the throne.

6. PRINCE HARRY

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As the second-born son of Prince Charles and Princess Diana, Prince Harry's place in the line is a regularly changing one. It changed earlier this week, when his brother William's third child arrived, and could change again if and when their family expands.

7. PRINCE ANDREW, DUKE OF YORK

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Prince Andrew is a perfect example of life before the Succession to the Crown Act 2013: Though he’s the second-born son of Queen Elizabeth and Prince Philip, he’s actually their third child (Princess Anne came between him and Prince Charles). But because the rules gave preference to males, Prince Andrew would inherit the throne before his older sister.

8. PRINCESS BEATRICE OF YORK

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Because Prince Andrew and his ex-wife, Sarah, Duchess of York, had two daughters and no sons, none of that male-preference primogeniture stuff mattered in terms of their placement. But with each child her cousin Prince William has, Princess Beatrice moves farther away from the throne. If Beatrice looks familiar, it might be because of the headlines she made with the Dr. Seuss-like hat she wore to William and Catherine’s wedding. (The infamous topper later sold on eBay for more than $130,000, all of which went to charity.)

9. PRINCESS EUGENIE OF YORK

Princess Eugenie of York arrives in the parade ring during Royal Ascot 2017 at Ascot Racecourse on June 20, 2017 in Ascot, England
Chris Jackson/Getty Images

Though she’s regularly seen at royal events, Prince Andrew and Sarah Ferguson’s youngest daughter spends the bulk of her time indulging her interest in fine art. She has held several jobs in the art world, and is currently a director at Hauser & Wirth’s London gallery.

10. PRINCE EDWARD, EARL OF WESSEX

 Prince Edward, Earl of Wessex leaves after a visit to Prince Philip
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Like his older brother Andrew, Prince Edward—the youngest son of Queen Elizabeth and Prince Philip—jumps the line ahead of his older sister, Princess Anne, because of the older rule that put males ahead of females.

11. JAMES, VISCOUNT SEVERN

 James, Viscount Severn, rides on the fun fair carousel on day 4 of the Royal Windsor Horse Show on May 11, 2013 in Windsor, England
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James, Viscount Severn—the younger of Prince Edward, Earl of Wessex and Sophie, Countess of Wessex’s two children, and their only son—turned 10 years old on December 17, 2017, and celebrated it as the 10th royal in line of succession. (The birth of the youngest Prince of Cambridge pushed him back a spot.)

12. LADY LOUISE MOUNTBATTEN-WINDSOR

Lady Louise Windsor during the annual Trooping the Colour Ceremony at Buckingham Palace on June 15, 2013 in London, England.
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Because the Succession to the Crown Act 2013 wasn’t enacted until 2015, Lady Louise Mountbatten-Windsor—the older of Prince Edward’s two children—will always be just behind her brother in the line of succession.

13. PRINCESS ANNE, THE PRINCESS ROYAL

Princess Anne, Princess Royal, visits the Hambleton Equine Clinic on October 10, 2017 in Stokesley, England
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Princess Anne, the Queen and Prince Philip’s second-born child and only daughter, may never rule over the throne in her lifetime, but at least she gets to be called “The Princess Royal.”

14. PETER PHILLIPS

Peter Phillips poses for a photo on The Mall
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The eldest child and only son of Princess Anne and her first husband, Captain Mark Phillips, stands just behind his mother in line. Interesting fact: Had Phillips’s wife, Autumn Kelly, not converted from Roman Catholicism to the Church of England before their marriage in 2008, Phillips would have lost his place in line.

15. SAVANNAH PHILLIPS

Savannah Phillips attends a Christmas Day church service
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On December 29, 2010, Peter and Autumn Phillips celebrated the birth of their first child, Savannah Anne Kathleen Phillips, who is also the Queen’s first great-grandchild. She’s currently 15th in line.

16. ISLA PHILLIPS

Princess Anne, Princess Royal, Isla Phillips and Peter Phillips attend a Christmas Day church service
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Less than two years after Savannah, Peter and Autumn Phillips had a second daughter, Isla, who stands just behind her sister in line. It wasn’t until 2017 that Savannah and Isla made their Buckingham Palace balcony debut (in honor of their great-grandmother’s 91st birthday).

17. ZARA TINDALL

 Zara Tindall arrives for a reception at the Guildhall
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Not one to hide in the background, Zara Tindall—Princess Anne’s second child and only daughter—has lived much of her life in the spotlight. A celebrated equestrian, she won the Eventing World Championship in Aachen in 2006 and was voted BBC Sports Personality of the Year the same year (her mom earned the same title in 1971). She’s also Prince George’s godmother.

18. MIA TINDALL

Mike Tindall, Zara Tindall and their daughter Mia Tindall pose for a photograph during day three of The Big Feastival at Alex James' Farm on August 28, 2016 in Kingham, Oxfordshire.
Tim P. Whitby/Getty Images

Zara Tindall’s daughter Mia may just be 4 years old, but she’s already regularly making headlines for her outgoing personality. And though she’s only 18th in line to the throne, her connection to the tippity top of the royal family is much closer: Prince William is her godfather.

19. DAVID ARMSTRONG-JONES, 2ND EARL OF SNOWDON

David Armstrong-Jones, 2nd Earl of Snowdon
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David Armstrong-Jones, the eldest child of Princess Margaret, isn’t waiting around to see if the British crown ever lands on his head. The 56-year-old, who goes by David Linley in his professional life, has made a name for himself as a talented furniture-maker. His bespoke pieces, sold under the brand name Linley, can be purchased through his own boutiques as well as at Harrods.

20. CHARLES ARMSTRONG-JONES, VISCOUNT LINLEY

Margarita Armstrong-Jones and Charles Patrick Inigo Armstrong-Jones
Chris Jackson-WPA Pool/Getty Images

David Armstrong-Jones’s only son, Charles, may be 20th in line to the throne, but the 18-year-old is the heir apparent to the Earldom of Snowdon.

21. LADY MARGARITA ARMSTRONG-JONES

Britain's Queen Elizabeth II (R) talks with Lady Margarita Armstrong-Jones (C) as her father David Armstrong-Jones (L), 2nd Earl of Snowdon, known as David Linley
HANNAH MCKAY/AFP/Getty Images

Lady Margarita Armstrong-Jones, the youngest child of David Armstrong-Jones and his only daughter, is also the only granddaughter of Princess Margaret. Now 15 years old (she'll turn 16 in June), Lady Margarita made headlines around the world in 2011 when she served as a flower girl at the wedding of Prince William and Catherine Middleton.

22. LADY SARAH CHATTO

Lady Sarah Chatto, the daughter of Princess Margaret arrives for her mother's memorial service
STEPHEN HIRD/AFP/Getty Images

Lady Sarah Chatto, Princess Margaret and Anthony Armstrong-Jones’s only daughter, is the youngest grandchild of King George VI and Queen Elizabeth the Queen Mother. In addition to serving as a bridesmaid to Princess Diana, she is Prince Harry’s godmother.

23. SAMUEL CHATTO

Lady Sarah Chatto (L) and her son Samuel Chatto (R) leave a Service of Thanksgiving for the life and work of Lord Snowdon at Westminster Abbey on April 7, 2017 in London, United Kingdom
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The first-born son of Lady Sarah Chatto and her husband, Daniel, has a long way to go to reach the throne: He’s currently 23rd in line.

24. ARTHUR CHATTO

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For better or worse, Sarah and Daniel Chatto’s youngest son Arthur has become a bit of a social media sensation. He's made headlines recently as he regularly posts selfies to Instagram—some of them on the eyebrow-raising side, at least as far as royals go.

25. PRINCE RICHARD, DUKE OF GLOUCESTER

Prince Richard, Duke of Gloucester makes a speech during the unveiling ceremony of London's first public memorial to the Korean War on December 3, 2014 in London, England
Carl Court/Getty Images

At 73 years old, Prince Richard, Duke of Gloucester is the youngest grandchild of King George V and Queen Mary. Formerly, he made a living as an architect, until the 1972 death of his brother, Prince William of Gloucester, put him next in line to inherit his father’s dukedom. On June 10, 1974, he officially succeeded his father as Duke of Gloucester, Earl of Ulster, and Baron Culloden.

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20 Black-and-White Facts About Penguins
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To celebrate World Penguin Day (which is today, April 25), here are a few fun facts about these adorable tuxedoed birds.

1. All 17 species of penguins are found exclusively in the Southern Hemisphere.

2. Emperor Penguins are the tallest species, standing nearly 4 feet tall. The smallest is the Little Blue Penguin, which is only about 16 inches.

emperor penguin
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3. The fastest species is the Gentoo Penguin, which can reach swimming speeds up to 22 mph.

Gentoo Penguin
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4. A penguin's striking coloring is a matter of camouflage; from above, its black back blends into the murky depths of the ocean. From below, its white belly is hidden against the bright surface.

penguins swimming in the ocean
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5. Fossils place the earliest penguin relative at some 60 million years ago, meaning an ancestor of the birds we see today survived the mass extinction of the dinosaurs.

emperor penguins
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6. Penguins ingest a lot of seawater while hunting for fish, but a special gland behind their eyes—the supraorbital gland—filters out the saltwater from their blood stream. Penguins excrete it through their beaks, or by sneezing.

penguins swimming in the ocean
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7. Unlike most birds—which lose and replace a few feathers at a time—penguins molt all at once, spending two or three weeks land-bound as they undergo what is called the catastrophic molt.

molting penguin
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8. All but two species of penguins breed in large colonies of up to a thousand birds.

king penguins
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9. It varies by species, but many penguins will mate with the same member of the opposite sex season after season.

chinstrap penguins
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10. Similarly, most species are also loyal to their exact nesting site, often returning to the same rookery in which they were born.

maegellic penguin nesting
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11. Some species create nests for their eggs out of pebbles and loose feathers. Emperor Penguins are an exception: They incubate a single egg each breeding season on the top of their feet. Under a loose fold of skin is a featherless area with a concentration of blood vessels that keeps the egg warm.

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12. In some species, it is the male penguin which incubates the eggs while females leave to hunt for weeks at a time. Because of this, pudgy males—with enough fat storage to survive weeks without eating—are most desirable.

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13. Penguin parents—both male and female—care for their young for several months until the chicks are strong enough to hunt for food on their own.

Penguins nest
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14. If a female Emperor Penguin's baby dies, she will often "kidnap" an unrelated chick.

penguin chicks
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15. Despite their lack of visible ears, penguins have excellent hearing and rely on distinct calls to identify their mates when returning to the crowded breeding grounds.

16. The first published account of penguins comes from Antonio Pigafetta, who was aboard Ferdinand Magellan's first circumnavigation of the globe in 1520. They spotted the animals near what was probably Punta Tombo in Argentina. (He called them "strange geese.")

17. An earlier, anonymous diary entry from Vasco da Gama's 1497 voyage around the Cape of Good Hope makes mention of flightless birds as large as ducks.

18. Because they aren't used to danger from animals on solid ground, wild penguins exhibit no particular fear of human tourists.

19. Unlike most sea mammals—which rely on blubber to stay warm—penguins survive because their feathers trap a layer of warm air next to the skin that serves as insulation, especially when they start generating muscular heat by swimming around.

20. In the 16th century, the word penguin actually referred to great auks (scientific name: Pinguinus impennis), a now-extinct species that inhabited the seas around eastern Canada. When explorers traveled to the Southern Hemisphere, they saw black and white birds that resembled auks, and called them penguins.

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