Many centuries ago, all people had to gather seeds and plants to eat. They did not know how to farm or raise animals for food. We call them the Stone Age people because they used stone tools and arms.

You may feel surprised in the world today there are still people who live like the Stone Age people. They live in the places that are hard to reach. Because they have met few people from the outside world, they rarely hear of modern inventions. They have not gained ways of doing things from others.

For 25, 000 years, groups of people have lived alone in the middle of Australia. One of thesegroups is the Arunta tribe (部落) . They do not know how to farm and how to raise sheep or cattle.

The Aruntas spend most of their time searching for food and water. The men hunt animals with stone-tipped spears. The women and children look for roots, seeds and nuts. They use sticks to dig up the roots. Several Arunta families live together. They have no house. At night, they sleep around small fires.

Now other people are moving into the center of Australia. Soon the Aruntas will no longer be a Stone Age people. Maybe that’s a piece of exciting news for them.

If you’re showering every day, you’re probably over doing it. In fact, showering too often can actually hurt your body in the long run.

As Time’s public health column explains, daily showers are common due to social norms more than any proper health need. We connect being freshly showered with being attractive and pleasing, so we tend to showering often to feel better.

But what’s the ideal shower frequency? In terms of your health — not how you look or smell — probably once or twice a week, assistant professor of dermatology at George Washington University, Dr. C. Brandon Mitchell says. “Your body is naturally a well-oiled machine,” he says. “A daily shower isn’t necessary.”

Of course, your situation may vary. If you have a job like car maintenance or construction, you’ll obviously have a visible layer of dirt you’ll need to wash off every single day. Similarly, if you work out every day, you may not have any health risks by washing every day, but you’ll still be smelly. If you feel like you need to take daily showers for aesthetic(审美的) reasons, at least make most of them light showers. “I tell patients who shower daily not to soap their whole bodies,” Mitchell says. Hit your pits, butt and groin, which are the areas that produce strong smells. The rest of your body doesn’t need much soaping, he says.

Too much time spent under the hot water can dry out your skin, cause cracks（裂纹）that can lead to infections or germs getting into your skin, and take away the natural oils on your skin that help keep it healthy. So, even if you’re aiming to be your most presentable, be sure to keep it moderate to avoid hurting your skin in the long run.

Lots of animals play. But the behavior is best known in mammals (哺乳动物) and birds. Now the scientists at London’s Queen Mary University report that bumblebees (大黄蜂) know the same thing. But before this, there were no reports of insects playing.

Dr. Lars Chittka began to wonder if bumblebees played during an earlier test. In that test, Chittka guided bumblebees to move balls into a goal for food. He noticed that some bees were rolling (滚动) balls even when they weren’t given food. He wondered if they were playing.

To test the idea, the scientists at his lab set up a new test. First, they numbered 45 young bumblebees between one and 23 days old. The numbers let them follow bumblebees’ behavior. Then, they set up a clear pathway from the bumblebees’ home to a feeding area. On either side of the open pathway, the researchers placed small colored wooden balls. On one side of the path, the balls couldn’t move. On the other side, the balls could roll around. For three hours a day, over 18 days, the scientists opened the pathway between the home and the feeding area. The bumblebees never had to leave the pathway to find food, but they left anyway. They weren’t interested in the side where the balls didn’t move, but they made lots of visits to the side with the rolling balls.

Catching the balls with their legs, the bees would move their wings to pull on the balls, causing them to roll. The 45 numbered bumblebees did this 910 times during the test. Though some only did it once, others did it a lot. The younger ones liked to spend more time rolling balls while the older ones showed less interest in it. One bee was recorded rolling balls 44 times in a single day. One was seen rolling balls 117 times over the whole test.

The test raises important questions about how the insects’ minds work and whether they have feelings.