Climate and Country Wealth
Why are some countries stupendously rich and others horrendously poor? Social theorists have been captivated by this question since the late 18th century, when Scottish economist Adam Smith argued in his magisterial work The Wealth of Nations that the best prescription for prosperity is a free-market economy in which the government allows business substantial freedom to pursue profits. Smith, however, made a cond notable hypothesis: that the physical geography of a region can influence its economic performance. He contended that the economies of coastal regions, with their easy access to a trade, usually outperform the economies of inland areas.
Coastal regions and tho near navigable waterways are indeed far richer and more denly ttled than interior regions, just as Smith predicted. Moreover, an area's climate can also affect its economic development. Nations in tropical climate zones generally face higher rates of infectious dia and lower agricultural productivity (especially for staple foods) than do nations in temperate zones. Similar burdens apply to the dert zones. The very poorest regions in the world are tho saddled with both handicaps: distance from a trade and a tropical or dert ecology. The basic lessons of geography are worth repeating, becau most economists have ignored them. In the past decade the vast majority of papers on economic development have neglected even the most obviou
s geographical realities.
The best single indicator of prosperity is gross national product (GNP) per capita – the total value of a country's economic output, divided by its population. A map showing
the world distribution of GNP per capita immediately reveals the vast gap between rich and poor nations. The great majority of the poorest countries lie in the
geographical tropics. In contrast, most of the richest countries lie in the temperate zones. Among the 28 economies categorized as high income by the World Bank, only
Hong Kong, Singapore and part of T aiwan are in the tropical zone, reprenting a
mere 2 percent of the combined population of the high-income regions. Almost all the temperate-zone countries have either high-income economies (as in the cas of North America, western Europe, Korea and Japan) or middle-income economies (as in the
cas of eastern Europe, the former Soviet Union and China). In addition, there is a strong temperate-tropical divide within countries that straddle both types of climates. Most of Brazil, for example, lies within the tropical zone, but the richest part of the nation – the southernmost states –is
in the temperate zone.
There are two major ways in which a region’s climate affects economic development. First, it affects the prevalence of dia. Many kinds of infectious dias are
endemic to the tropical and subtropical zones. This tends to be true of dias in
which the pathogen spends part of its life cycle outside the human host: for instance, malaria (carrie光顾
d by mosquitoes) and helminthic infections (caud by parasitic
worms). Although epidemics of malaria have occurred sporadically as far nort2010年出生
h as
Boston in the past century, the dia has never gained a lasting foothold in the temperate zones, becau the cold winters naturally control the mosquito-bad
transmission of the dia. Winter could thus be considered the world's most
effective public health intervention. It is much more difficult to control malaria in
tropical regions, where transmission takes place year-round and affects a large part of the population.
According to the World Health Organization, 300 million to 500 million new cas of malaria occur every year, almost entirely concentrated in the tropics. Widespread
illness and early deaths obviously hold back a nation's economic performance by significantly reducing worker productivity. But there are also long-term effects that may be amplified over time through various social feedbacks. A high incidence of dia can alter the age structure of a country's population. Societies with high levels
of child mortality tend to have high levels of fertility: mothers bear many children to guarantee that at least some will survive to adulthood. Young children will therefore constitute a large proportion of that country's population. With so many children, poor families cannot invest much in each child's education. High fertility also constrains the role of women in society, becau child rearing takes up so much of their adult lives.
Moreover, temperature affects agricultural productivity. Of the major food grains – wheat, maize and rice – wheat grows only in temperate climates, and maize and rice crops are generally more productive in temperate and subtropical climates than in
tropical zones. On average, a hectare of land in the tropics yields 2.3 metric tons of maize, whereas
a hectare in the temperate zone yields 6.4 tons. Farming in tropical rain-forest environments is hampered by the fragility of the soil: high temperatures mineralize the organic materials, and the inten rainfall leaches them out of the soil. In tropical environments that have wet and dry asons–such as the African
savanna–farmers must contend with the rapid loss of soil moisture resulting from high temperatures, the great variability of precipitation, and the ever prent risk of drought. Moreover, tropical environments are plagued with diver infestations of pests and parasites that can devastate both crops and livestock.
Moderate advantages or disadvantages in geography can lead to big differences in
long-term economic performance. Favorable agricultural or health conditions may
boost per capita income in temperate-zone nations and hence increa the size of their economies. The resulting inventions further rai economic output, spurring yet more inventive activity. The moderate geographical advantage is thus amplified through innovation. In contrast, the low food output per farm worker in tropical regions tends to diminish the size of cities. With a smaller proportion of the population in urban
areas, the rate of technological advance is usually slower. The tropical regions
therefore remain more rural than the temperate regions, with most of their economic activity
concentrated in low-technology agriculture rather than in high-technology
manufacturing and rvices.
Geographical factors, however, are only part of the story. Social and economic institutions are critical to long-term economic performance. It is particularly instructive to compare the post-World War II performance of socialist and free-market economies in neighboring countries that share the same geographical characteristics: North and South Korea, East and West Germany, the Czech Republic and Austria, and Estonia and Finland. In each ca we find that free-market
institutions vastly outperformed their counterparts.
If the findings are true, the policy implications are significant. Aid programs for developing countries will have to be revamped to specifically address the problems impod by climate and geo
graphy. In particular, new strategies have to be formulated that would help nations in tropical zones rai their agricultural productivity and reduce the prevalence of dias such as malaria.
Yawn
While fatigue, drowsiness or boredom easily bring on yawns, scientists are discovering there's more to yawning than most people think. Not much is known about why we yawn or if it rves any uful function, and very little rearch has been done on the subject. However, there are veral theories about why we yawn. Here are the four most common:
The physiological theory: Our bodies induce yawning to draw in more oxygen or remove a buildup of carbon dioxide. This theory helps explain why we yawn in groups. Larger groups produce more carbon dioxide, which means our bodies would act to draw in more oxygen and get rid of 手绘图
the excess
carbon dioxide. However, if our bodies make us yawn to draw in needed oxygen, wouldn't we yawn during exerci? Robert Provine, a developmental neuroscientist at the University of Maryland, Baltimore County and a leading expert on yawning, has tested this theory: Giving people additional oxygen didn't decrea yawning, and decreasing the
amount of carbon dioxide in a subject's environment also didn't prevent yawning.
The evolution theory: Some think that yawning began with our ancestors, who ud yawning to show their teeth and intimidate others. An offshoot of this theory is the不胫而走的意思
idea that yawning developed from early man as a signal for us to change activities. Another speculated reason for yawning is the desire to stretch one's muscles. Yawns are often accompanied by the urge to stretch. Prey animals must be ready to physically exert themlves at any given moment. There have been studies that suggest yawning, especially psychological "contagious" yawning, may have developed as a way of keeping a group of animals alert. If an animal is drowsy or bored, it may not be as alert as it should to be prepared to spring into action. Therefore, the "contagious" yawn could be an instinctual reaction to a signal from one member of the "herd" reminding the others to stay alert. Nervousness has also been
suggested as a possible reason. Nervousness often indicates the perception of an impending need for action. Anecdotal evidence suggests that yawning helps increa the state of alertness of a person. Paratroopers have been noted to yawn in the moments before they exit the aircraft.
The brain-cooling theory: A more recent theory propod by rearchers is that since people yawn more in situations where their brains are likely to be warmer -- tested by having some subjects breathe through their nos or press hot or cold packs to their foreheads -- it's a way to cool down their brains. In 2007, rearchers, including a professor of psychology, from the University of Albany propod that yawning may be a means to keep the brain cool. Mammalian brains operate best within a narrow temperature rancad打断
ge. In two experiments, they demonstrated that both subjects with cold packs attached to their foreheads and subjects asked to breathe strictly nasally exhibited reduced contagious yawning when watching videos of people yawning.
A similar recent hypothesis is that yawning is ud for regulation of body temperature. Similarly, a study by Jared Guttmann at Worcester Polytechnic Institute found that when a subject wearing earplugs yawned, a breeze is heard caud by the flux of the air moving between the subject's ear and the environment. Rearcher Guttmann determined that a
yawn caus one of three possible situations to occur: the读书好习惯
brain cools down due to an influx or outflux of oxygen, the pressure in the brain is reduced by an outflux of oxygen, or the pressure of the brain is incread by an influx of air caud by incread cranial space. What does it matter if our brains are cold or hot? Cool brains can think more clearly; hence, yawning might have developed to keep us alert.
Interestingly, while all vertebrates (including fish) yawn, only humans, chimps and possibly dogs find yawns contagious. And people don't find them contagious until they're about 4 years old. Recent studies show contagious yawning may be linked to one's capacity for empathy. In one study, autistic and non-autistic children were shown videos of people yawning and people simply moving their mouths. Both groups of kids yawned the same amount when viewing the video of people moving their mouths. But the non-autistic kids yawned much more frequently than tho with autism when watching people really yawning.
Since autism is a disorder that affects a person's social interaction skills, including the ability to empathize with others, the autistic kids' lack of yawning when watching others do so could indicate t
hey're less empathetic. The study also found the more vere a child's autism, the less likely he or she was to yawn. On a positive note, someday doctors may be able to diagno cognitive disabilities in young children more easily by eing whether or not they can catch a yawn from other.
So even though we still don't know for sure why we yawn, we do know lots of interesting things about yawning: you start yawning in utero; you yawn when you're aroud; more than half of you will yawn if you e someone el yawn; and reading about yawning makes you yawn.
