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世界人口 The World s Population
The first fifty years of the next millennium will be critical for the world's population. By 2050 population growth should have leveled off, but by then we'll have 10 billion people--two-thirds as many again as we have today. The rate of population growth is something we can choose right now, though: it's not something that just happens, but a matter of human choice. The choice is a complicated one,with many variables, but it remains a choice.
If we want to prevent a population explosion, we should take action now -or assist the poorer countries to do so. They need better government, better institutions, better labor and capital markets, better schools. Anything that increases the value of women's time and adds to the cost of caring for a child makes a woman less likely to have that child. Since big families are often seen as safety nets for illness and old age, improving poor people's access to insurance, pensions and welfare institutions also has a major impact. This can be as simple as rural credit, providing a means of saving. Finally, there is education--both for women and, perhaps even more important, for the next generation of children.
These steps are there to be taken, but there appear to be some countries that are not seriously trying at the moment. If we cannot achieve that we will certainly not control population.
That said, I don't feel pessimistic that we are going to run out of resources: we are becoming more efficient at producing food faster than the rate at which population is increasing. There is, however, a risk that we will wreck the environment so effectively that the world will no longer be an attractive place to live. That really would be a dismal outcome, to reach world population equilibrium only to find we'd destroyed the natural environment in the process.
The difference between a brain and a computer can be expressed in a single word:complexity.
Even the most complicated computer man has yet built can't compare in intricacy with the brain. Computer switches and comportents number in the thousands rather than in the billions.What's more, the computer switch is just an on-off device,whereas the brain cell is itself possessed of a tremendously complex inner structure.
Can a computer think? That depends on what you mean by "think". If solving a mathematical problem is "thinking", then a computer can "think" and do so much faster than a man. Of course, most mathematical problems can be solved quite mechanically by repeating certain straightforward processes over and over again. Even the simple computers of today can be geared for that.
Surely, though, if a computer can be made complex enough, it can be as creative as we are. If it could be made as complex as a human brain, it could be the equivalent of a human brain and do whatever a human brain can do.
But how long will it take to build a computer complex enough to duplicate the human brain? Perhaps not as long as some think. Long before we approach a computer as complex as our brain, we will perhaps build a computer that is at least complex enough to design another computer more complex than itself. This more complex computer could design one still more complex and so on and so on and so on.
In other words, once we pass a certain critical point, the computers take over and there is a "complexity explosion". In a very short time thereafter, computers may exist that not only duplicate the human brain--but far surpass it.
不要伤害蜘蛛 Spare that spider
Why, you may wonder, should spiders be our friends? Because they destroy so many insects, and insects include some of the greatest enemies of the human race.Insects would make it impossible for us to live in the world; they would devour all our crops and kill our flocks and herds, if it were not for the protection we get from insect-eating animals.We owe a lot to the birds and beasts who eat insects but all of them put together kill only a fraction of the number destroyed by spiders.Moreover, unlike some of the other insect eaters, spiders never do the least harm to us or our belongings.
Spiders are not insects, as many people think, nor even nearly related to them.One can tell the difference almost at a glance, for a spider always has eight legs and an insect never more than six.
How many spiders are engaged in this work on our behalf? One authority on spiders made a census of the spiders in a grass field in the south of England, and he estimated that there were more than 2,250,000 in one acre; that is something like 6,000,000 spiders of different kinds on a football pitch.Spiders are busy for at least half the year in killing insects.It is impossible to make more than the wildest guess at how many they kill, but they are hungry creatures, not content with only three meals a day.It has been estimated that the weight of all the insects destroyed by spiders in Britain in one year would be greater than the total weight of all the human beings in the country.