FAITH LAPIDUS: This is SCIENCE IN THE NEWS in VOA Special English. I'm Faith Lapidus.
BOB DOUGHTY: And I'm Bob Doughty. This week, we will tell how sharks use their wonderful sense of smell to find food. We also will tell about what some researchers are calling the world's oldest leather shoe. And, we will have some good news for people fifty years of age and up.
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FAITH LAPIDUS: Few creatures on earth are as good as sharks at finding their dinners. People often say that a shark follows its nose to its meals. Now, scientists have learned more about how those noses work to help the much-feared fish direct its movements.
Recently published research questions a common belief about sharks.
Some people think that sharks simply follow the strongest smells that reach them to find their prey, or target. But scientists now can show that differences between the time when a shark's nostrils receive smells is more important than the strength of the odors.
Researchers Jayne Gardiner and Jelle Atema reported their findings in the publication Current Biology.
BOB DOUGHTY: The researchers studied small sharks called smooth dogfish, common to America's New England coast. The animals were swimming in a tank or container.
The scientists placed special equipment on the sharks to direct odors directly to their nostrils. The smells were from squids -- a favorite meal of the smooth dogfish shark.
Then the scientists watched and recorded which way the sharks turned to follow the odor.
Ms. Gardiner said the delay between the arrival of the smell at each nostril could be as little as a half second or less. The animals turned and swam in the direction of the nostril that first received the odor. Ms. Gardiner said this was true even if the odor in the second nostril was stronger.
Following the odor received by the first nostril guided the sharks into smelly areas in the water. The fish then followed the odors to the squid.
FAITH LAPIDUS: The findings also led the researchers to consider why some sharks have strangely shaped heads. The hammerhead shark family is a good example. The name hammerhead describes the animal's wide, flat head. One theory is that the shape developed over the ages to improve this shark's sense of smell.
When hammerheads swim into clouds of odor, they usually do not swim straight on. Instead, their bodies are on an angle.
BOB DOUGHTY: Hammerhead sharks have nostrils that are more widely spaced than those of sharks with pointed noses. The placement creates a longer delay between the time the left and right nostrils receive an odor than in sharks with pointed noses.
This suggests that animals with more widely spaced nostrils could attack from better positions while swimming fast. Ms. Gardiner believes this ability may have helped the development of hammerhead sharks over the ages.
Comparison of underwater odors is the idea behind some mechanical searching devices now in use by the military. These robots use odors to seek underwater bombs. Ms. Gardiner suggests that the current research with sharks may lead to better robotic devices.
Jayne Gardiner is a doctoral candidate at the University of South Florida. Professor Atema works with Boston University and the Marine Biological Laboratory at the Woods Hole Oceanographic Institution, both in Massachusetts.
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FAITH LAPIDUS: Nothing fits like an old shoe -- especially if that shoe walked the earth five thousand five hundred years ago. Researchers in Armenia found the world's oldest leather shoe, and they say it was in surprisingly good condition.
Doctoral student Diana Zardaryan of the Institute of Archeology found it in a cave near the border with Iran and Turkey. In her words, "even the shoe laces were preserved."
It fact, the team of archeologists first thought it was about six or seven hundred years old. Then two laboratories in the United States and Britain did radiocarbon tests.
The tests showed it was four hundred years older than the Stonehenge formation in England -- and a thousand years older than the Great Pyramid of Giza in Egypt.
BOB DOUGHTY: The cool and dry conditions in the cave protected the shoe and other objects. So did a thick, solid layer of sheep dung covering the floor. This acted as a seal to prevent damage.
The shoe was made from a single piece of cowhide. The researchers believe the shoe was shaped to fit the wearer's right foot. The shoe is small -- a European size thirty-seven, or a women's size seven in the United States.
FAITH LAPIDUS: The lead author of the research says he does not know if the shoe was made for a man or a woman. Ron Pinhasi of University College in Cork, Ireland, says it could have fit a man from that period.
His team also found grass placed inside the shoe. The researchers say the grass might have been used to keep the wearer's foot warm. Or it could have been used to hold the shape of the shoe while it was not being worn.
The shoe is similar in design to "pampooties." These were shoes worn on the Aran Islands, in the west of Ireland, until the nineteen fifties. This kind of shoe appears to have been worn for thousands of years across a large area of Europe and beyond.
BOB DOUGHTY:
The researchers also found large containers of wheat, barley and apricots in the cave, along with a broken pot and sheep's horns. They also found the graves of children buried near the back of the cave. They do not know why all these things were found together in one place. They do not know what the purpose of the cave was.
The archeologists published their findings in the online scientific journal PloS One, from the Public Library of Science. They are continuing their work in Armenia. They say there are many other parts of the cave they have yet to explore.
The oldest footwear of any kind ever found are sandals made of plant material. Scientists believe sandals found in the Arnold Research Cave in the American state of Missouri are about seven thousand five hundred years old.
That makes them about two thousand years older than the leather shoe found in Armenia.
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FAITH LAPIDUS: Finally, old age does not sound exciting to most people. But a recent study offers good news for older adults.
It found that people become happier and experience less worry after they reach the age of fifty. In fact, by age eighty-five, people are happier with their life than when they are eighteen years old.
The findings came from a study of more than three hundred forty thousand adults living in the United States. The Gallup Organization questioned them by telephone in two thousand eight. At the time, the adults were between the ages of eighteen and eighty-five years old.
BOB DOUGHTY: The researchers asked questions about emotions like happiness, sadness and worry. They also asked about mental or emotional tension -- better known as stress.
Arthur Stone was a leader of the study. He works for the Department of Psychiatry and Behavioral Science at Stony Brook University in New York. His team found that levels of stress were highest among adults between the ages of twenty-two and twenty-five.
The study found that stress levels dropped sharply after people reached their fifties.
FAITH LAPIDUS: Surprisingly, people in their seventies and eighties were least likely to report feeling negative or harmful emotions.
Happiness was highest among the youngest adults and those in their early seventies. The study showed that men and women had similar emotional patterns as they grew older. However, women reported more sadness, stress and worry than men at all ages.
The Proceedings of the National Academy of Sciences published a report about the study.
BOB DOUGHTY: Researchers do not know why happiness increases as people get older.
One idea is that, as people age, they grow more thankful for what they have, and have better control of their emotions. They also spend less time thinking about bad experiences.
Professor Stone says the emotional patterns could be linked to changes in how people see the world, or maybe even changes in brain chemistry.
The researchers considered other possible influences, like having young children, being unemployed and being single. However, such influences did not affect the levels of happiness and well-being related to age.
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FAITH LAPIDUS: This SCIENCE IN THE NEWS was written by Brianna Blake, Jim Tedder and Jerilyn Watson. Our producer was June Simms. I'm Faith Lapidus.
BOB DOUGHTY:
And I'm Bob Doughty. Join us again next week for more news about science in Special English on the Voice of America.