Cities usually have a good reason for being where they are, like a nearby port or river. People settle in these places because they are easy to get to and naturally suited to communications and trade. New York City, for example, is near a large harbour at the mouth of the Hudson River. Over 300 years its population grew gradually from 800 people to 8 million. But not all cities develop slowly over a long period of time. Boom towns grow from nothing almost overnight. In 1896, Dawson, Canada, was unmapped wilderness(荒野). But gold was discovered there in 1897, and two years later, it was one of the largest cities in the West, with a population of 30,000.

Dawson did not have any of the natural conveniences of cities like London or Paris. People went there for gold. They travelled over snow-covered mountains and sailed hundreds of miles up icy rivers. The path to Dawson was covered with thirty feet of wet snow that could fall without warming. An avalanche(雪崩) once closed the path, killing 63 people. For many who made it to Dawson, however, the rewards were worth the difficult trip. Of the first 20,000 people who dug for gold, 4,000 got rich. About 100 of these stayed rich men for the rest of their lives.

But no matter how rich they were, Dawson was never comfortable. Necessities like food and wood were very expensive. But soon, the gold that Dawson depended on had all been found. The city was crowded with disappointed people with no interest in settling down, and when they heard there were new gold discoveries in Alaska, they left Dawson City as quickly as they had come. Today, people still come and go — to see where the Canadian gold rush happened. Tourism is now the chief industry of Dawson City — its present population is 762.

In the laboratory，chimps don’t naturally share food either．If a chimp is put in a cage where he can pull in one plate of food for himself or，with no great effort，a plate that also provides food for a neighbor to the next cage，he will pull at random﹣he just doesn’t care whether his neighbor gets fed or not．Chimps are truly selfish．

Human children，on the other hand are extremely corporative．From the earliest ages，they decide to help others，to share information and to participate a achieving common goals．The psychologist Michael Tomasello has studied this cooperativeness in a series of expensive with very young children．He finds that if babies aged 18months see an worried adult with hands full trying to open a door，almost all will immediately try to help．

There are several reasons to believe that the urges to help，inform and share are not taught．but naturally possessed in young children．One is that these instincts appear at a very young age before most parents have started to train children to behave socially．Another is that the helping behaviors are not improved if the children are remanded．A third reason is that social intelligence．Develops in children before their general cognitive（认知的）skills，at least when compared with chimps. In tests conducted by Tomasello，the children did no better than the chimps on the physical world tests，but were considerably better at understanding the social world

The cure of what children’s minds have and chimps’ don’t in what Tomasello calls what．Part of this ability is that they can infer what others know or are thinking．But that，even very young children want to be part of a shared purpose．They actively seek to be part of a “we”，a group that intends to work toward a shared goal．

The weather effects both good and bad，are felt in many places．Rich countries gain more from powerful Nino，on balance，than they lose．A study found that a strong Nino in 1997helped American’s economy grow by 15billion，partly because of better agricultural harvest，farmers in the Midwest gained from extra rain．The total rise in agricultural in rich countries in growth than the fall in poor ones．