Fishing is a popular activity and every fisherman knows the rule: keep the big ones, throw the smaller ones back. The reason for it is simple—if you keep the smaller ones, fewer fish will be able to grow and reproduce (繁殖), and the fish population will be in danger. But should we always keep the big ones?

One scientist, Dr. David Conover, has spent the last 10 years studying the effects of the “keep the big ones” rule.

To set up his experiment, Conover and his team caught hundreds of silverside fish and divided them into six groups. For two groups, Conover followed the “keep the large ones” rule and took out the biggest fish. For two other groups, he removed only the small fish. For the last two groups, he removed fish randomly (随机地).

After five years, he measured the fish in each group. In the two groups where the largest fish were regularly removed, the average (平均) fish size was smaller than the average size in the other groups. That is to say, if only small fish survive to reproduce, then future generations of fish are likely to be small.

For the second five years of his experiment, Conover changed the rules and took fish randomly from each group. At the end of the experiment, he found that the fish that were in the “keep the large ones” group for the first five years had started to get larger again, although he expected it would take at least 12 years for the fish in that group to return to their normal size. In other words, it takes less time to shrink (变小) than it does to recover.

Like many people, I have no clear idea about heroes. At some point, we all wonder if we need a hero and what a hero really is.

Although there are a lot of differences in cultures, heroes around the world generally share a number of characteristics which give us courage and make us want to learn from them.

A hero does something worth (值得) talking about. A hero has a special story to tell and people think highly of (高度评价) it. But a hero is not just the person with great power fame (声誉).

A hero has powers (力量) larger than himself. Some people want to live like a hero, and they have to experience life with new and further meaning. A sure test for would-be heroes is what or whom they serve. What do they want to live and die for? If the answer suggests (暗示) they serve only their own fame, they may be famous persons but not heroes.

A hero has a vision from the mountaintop. He has the power to move people. He creates new possibilities. Without Gandhi, India might still be part of Britain. Without Martin Luther King, Jr, Americans might take different buses, cat in different restaurants; go for walks in different parks, and shop in different stores because of the different colours of their skin.

There might be changes in society without a hero, but the speed of change would be rather slow. Thanks to heroes in history, they make the society develop so rapidly.

In today’s world of modern science and medicine, a more traditional treatment is once again becoming popular—animal friendship.

It is now well-known that people with problems such as heart disease or cancer live longer and get better more quickly if they have pets. Keeping pets lowers blood pressure and makes people less worried. Animals are increasingly important in treating older people who have memory loss and other brain problems. These people often feel nervous and upset. Activities with animals help them improve their physical condition and also give them joy, entertainment and loving friendship.

Here is a case that shows the benefits of animals. John was a six-year-old mute. He had no physical problems. He just refused to talk. His older cousin, Ned, had a parrot called Sally, and John used to visit it. When he arrived, Ned used to say, “Hi, John!” We all know parrots copy what they hear. After a few visits, Sally began saying, “Hi, John!” when John came into the room. Then, one day, John turned to the parrot and replied, “Hi, Sally!” Staying with the parrot encouraged John to begin talking.

Another use of animal helpers is in schools. In some cases, animals are used to help children with physical or personal problems. In other cases, they are used to teach children to get on and share with others, and even to teach them about animals.

If you want to know more about animal helper programmes, you can get in touch with organizations like Riding for the Disabled or do a search under “animal therapy” on the Internet. You don’t have to be an animal trainer or a doctor to Join in.