If you need help herding some sheep or retrieving a stick, you can count on your canine companion(伴犬) because dogs always seem to be keen on lending a paw. But only if their partner is a person. When it comes to cooperating with one another, dogs are truly lost－and instead it’s wolves who’ve mastered the art of teamwork. That’s according to a study in the Proceedings of the National Academy of Sciences.

For thousands of years, humans have been breeding (饲养) dogs that can do all sorts of neat tricks. And because dogs aim to please, we’ve come to think that domestication(驯养) has somehow boosted dogs’ powers of cooperation. But researchers in Austria have been wondering whether that idea could be barking up the wrong tree. Because left to their own devices, dogs are bigger loners than wolves.

“So wolves live in closely knit family packs, they cooperate in raising the young, they also cooperate in hunting and in defending their territories. So they really have a strong dependence on cooperation in many aspects of their lives. In contrast, to this free ranging dogs actually forage (觅食) mostly by themselves. It’s only mothers that raise their young. And they do form packs but they tend to be somewhat more fluid(不固定的), if you want.”

That’s Sarah Marshall-Pescini of the Wolf Science Center at the University of Vienna. She and her colleagues decided to test dogs’ and wolves’ relative powers of cooperation. In the setup, a pair of animals—either two dogs or two wolves—is presented with a contraption(装置) that will allow the participants to access a plate of food—but only if both members of the team pull on the two ends of a rope at the same time.

A dozen wolves and 14 dogs took the challenge. And the results? The wolves ran circles around their doggie descendants. In some 400 attempts, the wolf teams scored a snack 100 times. Which may not sound all that impressive…until you compare it with the doggie duos, who, in nearly 500 trials, succeeded only twice.

Now, it’s not that dogs are less avid learners. Or that they turned tail and avoided the apparatus. Marshall-Pescini says the dogs were curious about the device.

“What seemed to be happening was they didn’t want to get into conflict with each other. So they wouldn’t both go and try things on it but rather took it in turns. And this really hindered(阻碍了) their capacity to cooperate.”So rather than step on each others’ toes, the dogs took turns bowing out, giving their teammate a chance at the plate. That show of social grace left the poor dogs with their tummies growling (饥肠辘辘). And no treat to wolf down.

(Source:Scientific American Oct. 25, 2017)

For many centuries, people have been enjoying the advantages of drinking green tea. Many people prefer drinking green tea to white tea and black tea, simply because it has a unique flavor (味道) that is not found in other types of tea. Nowadays, keeping the natural greenish color of tea leaves remains just like before. This is done by preparing the green tea just like the way it was prepared before—by washing the leaves right after picking them, then boiling them.

Many people think that drinking green tea helps a lot in improving the general health of their body. For a long time, there has been the belief that green tea can help people to cure (治愈) beriberi disease，lower the blood pressure, treat wounds, and even prevent tiredness. Now, modern technology finds out that there are even more health advantages. It can reduce the possibility of having heart disease and cancer and help people to lose weight more easily.

It has been proved that green tea has a high level of vitamin P, which is very important to human health. Besides, studies have found out that green tea has polyphenol (多酚), which is believed to be stronger than vitamin C and vitamin E.

 Having two cups of green tea daily is a good routine for your body. However, most doctors would suggest drinking at least 4 cups a day. You can slowly increase the amount you drink to allow your body to get used to it. There is nothing to lose but everything to gain in drinking green tea.

Most of the suggestions about exercise are pretty clear— do something—anything—to get moving. Any activity is better than no activity, so simply letting the body move is what's important. And there's a good reason for the simplicity of that message—with one third of Americans not exercising at all, the easier the advice, the better

   But for those who follow those suggestions and get regular exercise, things could be a little more difficult to deal with. How far is too far when it comes to pushing your body? Overdoing exercise can lead to injuries, and may end up removing all the benefits physical activity can have.

   Our bodies are trained to adapt, so even if you run or bike every day, at a certain point, your body starts to coast. Your muscles don't work as hard, your heart doesn't beat as quickly, and you don't breathe as heavily to pump oxygen to your cells. "When you hit a plateau (稳定状态), it is your body getting used to an activity. You have achieved your body's potential for that activity." says Scott Danberg, Director of Fitness. "If you keep working at the same activity, it's impossible sometimes to keep moving up. It means you are still in great shape, but you have to start changing things to move forward."

   So how do you make sure that your exercise continues to work for you? Some fitness trainers recommend changing workouts every four to six weeks to strengthen the body. Others say that the best test is whether your workout challenges you—if you're breathing hard and feel tired after exercising, then you're harvesting the benefits of that workout, whatever it might be.

   And how do you know if you're pushing too hard? While putting some stress on the body is required to improve fitness, Barbara Bushman, a professor at Missouri State University, says exercise overload can cause injury. "Typically for beginners, gradual increases in duration (期间) are recommended until the person is comfortable with longer exercise duration. Then the duration might be cut back a bit but the stress increased. The idea is not to increase all areas at once," she says.

   Figuring out when to push and when to pull back isn't an exact science. Genes, for example, influence metabolic rates(代谢速率)and body types, both of which contribute to fitness. One of the best ways to find the most effective exercise plan for you—suited to your body type and your fitness goals—is to regularly step back. A doctor or trainer can help, or you can try the assessments (评估)from the American College of Sports Medicine (ACSM). A good check-in should include your heart rate and body composition. Tracking these measures while you exercise will not only tell you how far you have progressed, but let you know if you've either hit a plateau or are overdoing the workouts.