1 . Like humans, dogs have tear ducts (泪腺) that well up with tears to keep their eyes clean and healthy. But tears in dogs, which tend not to fall as they do when humans cry, hadn’t been linked with emotion before.

Takefumi Kikusui, a professor at Azabu University in Japan, decided to study dog tears after watching his poodle (鬟毛狗) when she had puppies six years ago. He noticed that her eyes got teary as she nursed her puppies. So Kikusui and his team measured tear production among 18 dogs with a standard test known as the Schirmer Tear Test (STT). It involved a paper strip placed inside the eyelids (眼睑) of the dogs for a minute before and after they were reunited with their owners following five to seven hours of separation.

“Tear production was evaluated by the length of the wet part on the STT. The baseline was about 22 mm, and the reunion with the owner increased the length by 10%,” Kikusui explained. With the help of 20 dogs, researchers then compared tear production before and after reunions with their owners and people with whom the animals were familiar. Only the reunion with the owner increased tear production.

Researchers also tested if oxytocin, a hormone thought to be connected to emotional bonding in humans and dogs, could be causing the tear production. They found that dropping oxytocin in dogs’ eyes really increased tear production, while a control solution did not.

The findings suggest “dogs’ tears are associated with positive emotions, such as a reunion with the owner,” according to Takefumi Kikusui. Still, some scientists think it’s a stretch to say that dogs cry tears of joy. “It would take a lot to let me accept the evidence of this research,” said Clive Wynne, an animal behavioral specialist at Arizona State University.

2 . A pair of best friends from Texas are proving that adventure doesn’t have an age limit — even when you’re 81.

Ellie Hamby, a photographer, and Sandy Hazelip, a physician, toured the world in 80 days, adventuring from the beaches of Bali to the deserts of Egypt.

Their first stop was Antarctica. “The beauty of the Antarctic is just unbelievable,” Hamby recalled. Since then, the pair have visited 18 countries across all seven continents.

And despite the challenges international travel presents, the best friends say they finished their trip without any arguments.

“We’re both independent, very stubborn. But we seem to allow each other to give space,” said Hamby. “We just understand each other and we know this is a good thing we’re doing and we kind of respect each other’s feelings.”

For Hamby, the most interesting aspect of the trip was the people they met along the way.

“We love all the sights that we saw, but the things that we remember the most are the people that we met,” she said. “We met some of the most wonderful, kindest, friendliest people in the world. We just have friends now all over the world that we love dearly.”

And they shared an important piece of advice for any travelers worried about the language barrier on their own adventures.

“You know, people ask us often about the language, how we manage it,” said Hamby. “We say with Sandy and Ellie, there’s one language and that’s a smile. And we found that worked wonders because we were often aware that there was not English spoken. But a smile covers all languages.”

3 . My photographs are the items I would definitely take or guard in case of an emergency. But what else? This was the question I asked myself as a ________ came toward us.

Unlike some friends and________, we decided to stay in our home. We didn’t have to choose what we would save by ________ it into the car, but we still had to decide what required protection by storing it in our walk-in closet. Surprisingly, few items made the cut - an obvious ________ that we had surrounded ourselves with beautiful yet unessential items. We needed ________ for the truly important things: ourselves.

Because when you hear the roar of the winds, or when something ________ hard against your windows, you don’t think of photos.You don’t worry about your big screen TV, or those paintings you’ve covered with towels to protect them, or that ________ car that you still haven’t finished paying for.

As ________ goes on outside, this is what you think: My children, are they OK? Are their impact-resistant(耐冲击的) windows working ________? Are their roofs keeping out the damage? My grandchildren, are they crying out in fear? Are they ________ as their own grandparents are? My relatives — yes, even those I try to avoid — have they ________ the worst of it? My friends, will they be forced to move somewhere else permanently? You don’t think about what you own but about what you love; what money can’t buy back.

Months and years after the hurricane, I often told people that there are two parts to ________ this kind of catastrophe: the horror of the hurricane itself and then the rebuilding that follows. The ________ together of a life, however, will take months, perhaps years.

But we will do it, ________ and as a community. Of that I have no doubt. In fact, I’ll make one more prediction. Piece by piece, item by item, we will once again collect the material possessions that decorate a home. I hate to admit this, but lessons learned ________ fear aren’t always long-lasting.

4 . Some ants have figured out how to avoid getting lost: build taller anthills, according to a recent study.

Desert ants living in the hot, flat salt pans of Tunisia spend their days looking for food and reach as far as 1.1 kilometers from their nests. To find their way home, desert ants use a navigation system, relying on the sun’s position and counting their steps to track their location relative to their nest.

But this system becomes increasingly unreliable as the distance from the nest increases. “We realized that, whenever the ants in salt pans came closer to their nest, they suddenly pinpointed the nest hill from several meters distance,” says Markus Knaden, a researcher at Max Planck Institute for Chemical Ecology. “This made us think that the hill serves as a nest-defining landmark.”

So Knaden and colleagues captured ants from nests in the middle of salt pans and from along their shorelines. Only salt-pan nests had distinct hills, up to 40 centimeters tall, whereas the hills on shoreline nests were lower or barely noticeable. Next, the team removed any hills and placed the captured insects some distance away from their nests. Salt-pan ants struggled more than shore ants to find homes. Shore ants relied on the shoreline for guidance and weren’t affected by the hill removal, the researchers concluded.

The team further conducted another study to see if desert ants were deliberately building a taller hill when their surroundings lacked any visible landmarks. So, the researchers removed the hills of 16 salt-pan nests and installed (安装) two 50-centimeter-tall blocks near eight of them. The other eight nests were left without any artificial visual aid. After three days, the researchers found that seven ants from the unaided nests had rebuilt their hills. But only two ants from the nests with man-made blocks nearby had bothered to rebuild.

“It implies that ants regularly assess the complexity of their environment and change their decisions based on their conclusion,” says ecologist Judith Bronstein of the University of Arizona.

As winter shortens and ice melts on Hudson Bay, a mother polar bear and her two cubs face danger brought on by climate change. Following the bear family, guide Dennis Compare witnesses achievements of survival and adaptability. The two-hour TV special Kingdom of the Polar Bears airs April 22 at 8/7c on Nat Geo WILD.

National Geographic Explorer Brian Skerry’s breathtaking photographs are at the heart of Secrets of the Whales. That’s the title of Skerry’s new book, on sale April 6, and the name of National Geographic’s documentary series, with filmmaker James Cameron executive producing and actor Sigourney Weaver narrating. It premieres (首映) April 22 on Disney.

Known for finding famous shipwrecks such as the Titanic, Robert Ballard shares not only his expeditions but also his personal challenges in a remarkable memoir. Into the Deep: An Explorer’s Life is available May 11 wherever books are sold.

Curious about your place in the universe? Cosmic Queries: Star Talk’s Guide to Who We Are, How We Got Here, and Where We’re Going offers the wit and wisdom of astrophysicist deGrasst Tyson and physicist James Trefil, illustrated with stellar photos. It’s available wherever books are sold.