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 at 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.
