SSS 2011-02-23
时间：2018-12-24 作者：英语课 分类：Scientific American(二)月
This is Scientific American's 60-Second Science. I'm Steve Mirsky. Got a minute?
"The ability to digest milk as adults, and as infants, actually, is due to the expression of an enzyme 1 called lactase." That's the University of Pennsylvania's Sarah Tishkoff at the AAAS conference in Washington DC on February 20th, talking about the recent evolution of lactose tolerance 2 in different human populations within the last 9,000 years. "Individuals who don't express this enzyme can't digest that complex sugar."
Can we put a number on the evolutionary 3 importance of lactose tolerance? "The selective pressure is quite remarkable 4. We actually estimated it to be about 10 percent. You're more likely to have 10 percent more offspring essentially 5."
How strong is that? Look at population genetics to see how fast a trait will spread that develops in one individual in a population and that confers a 10 percent reproductive advantage. A mathematical analysis reveals that in just 100 generations, such a trait can be found in 95 percent of the individuals in the population.
That time period could be less than 2,000 years for humans. "I'm often asked the question, are humans still evolving? I would say the answer is absolutely yes."
- Above a certain temperature,the enzyme molecule will become unfolded.超过一定温度，酶分子将会展开。
- An enzyme that dissolves the fibrin of blood clots.能溶解血凝块中的纤维的酶。
- Tolerance is one of his strengths.宽容是他的一个优点。
- Human beings have limited tolerance of noise.人类对噪音的忍耐力有限。
- Life has its own evolutionary process.生命有其自身的进化过程。
- These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。
- She has made remarkable headway in her writing skills.她在写作技巧方面有了长足进步。
- These cars are remarkable for the quietness of their engines.这些汽车因发动机没有噪音而不同凡响。
- Really great men are essentially modest.真正的伟人大都很谦虚。
- She is an essentially selfish person.她本质上是个自私自利的人。