NT_020
听力音频：
综合写作
For hundreds of thousands of years of human history, the human brain steadily grew in size. However, about 20,000 years ago, the size of the human brain began to decrease. Since then, the size of the average brain has decreased by about 10 percent. Scientists are not sure why the human brain has become smaller, but several theories have emerged to explain the phenomenon.
Climate Changes
Some scientists believe that the decrease in human brain size is a result of the decrease in the overall size of the human body, which has been caused by changes in Earth’s climate. Over the past 20,000 years Earth’s climate has experienced a warming trend. Generally, warmer climate favors smaller body size; therefore, as Earth’s climate warmed, the size of the human body decreased, and the size of the human brain decreased with it.
Agriculture
Other researchers believe that the change to an agricultural lifestyle contributed to decreased brain size. Our ancestors’ large brains needed large quantities of proteins and vitamins to remain healthy. After the agricultural revolution, people’s diets consisted mostly of grains, but grains are lower in proteins and vitamins than non-agricultural diets. People with slightly smaller brains had an advantage: they were not as affected by the low-protein diet. Over time, they became the majority.
Decrease in Muscle Mass
According to a third theory, the smaller size of the human brain reflects the fact that humans today have smaller muscles than humans did 20,000 years ago. This is important because much of the brain is used to control muscles. As humans became less muscular, the parts of the brain that controlled muscles also became smaller, resulting in an overall reduction in brain size.
听力原文
listen to part of a lecture on the topic you just read about. Unfortunately, all the theories you just read are flawed. None adequately explains why the human brain started to become smaller 20,000 years ago.
First, the theory that changes in brain size reflect climate changes doesn’t really hold up. If we look at the human brain in the period before 20,000 years ago, we see that brain size did not correspond closely to temperature changes. Earth’s temperature went up and down several times during this early period, but brain size did not decrease and increase as. The temperature went up and down. Instead, the brain grew steadily larger and larger. So since brain size was not strongly linked to temperature in an earlier period, there’s no reason to believe it’s been linked to temperature in the last 20,000 years.
the idea that smaller brain size is linked to agriculture, the decrease in brain size has occurred all over the world including. Those areas where grain based agriculture did not appear until very recently. In Australia and southern Africa, for example, grain based agriculture was not practiced until almost modern times. Yet, humans living in those areas experience the same decline in brain size at the same time as the rest of the world.
The problem with the third theory is that our muscles are only a little bit smaller than they were 20,000 years ago, but our brain size has decreased much more than we would predict from this small decrease in muscle mass. So, while the small loss of muscle may have contributed to the decrease in brain size, it was just a minor factor that cannot fully explain the decrease. There must be other more important factors that have caused the large decrease in human brain size.
独立写作
Question:
Do you agree or disagree with the following statement?
For success in school or work, having the ability to adapt or adjust to changing conditions or circumstances is more important than having excellent knowledge of a job or a field of study.
Use specific reasons and examples to support your answer.
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