“The ability to digest milk as adults, and as infants, actually, is due to the expression of an enzyme called lactase.” That’s the University of Pennsylvania’s Sarah Tishkoff at the AAAS conference in Washington, D.C., on February 20th, talking about the recent evolution of lactose tolerance in different human populations within the past 9,000 years. “Individuals who don’t express this enzyme can’t digest that ____1____.”
Can we put a number on the ____2____ of lactose tolerance? “The selective pressure was quite ____3____. We actually estimated it to be about 10 percent. So you’re more likely to have 10 percent more offspring essentially.”
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 ____4____. A ____5____ 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.”
【视听版科学小组荣誉出品】
complex sugar evolutionary importance remarkable reproductive advantage mathematical analysis
“实际上，对于小孩子和成年人来讲，当身体内表达一种叫乳糖酶的蛋白时，他们才能消化牛奶。” 二月二十日，在华盛顿的美国科学发展协会会议上，谈起过去9000年来不同人身体中乳糖耐受性的最新进化，宾夕法尼亚州大学的萨拉•特斯科夫这样说道。“不表达这种酶的人不能消化这种复糖。” 我们可以用数字来衡量乳糖耐受性在进化史上的重要程度吗？“选择压力非常显著。实际上我们预测有10%的人具有乳糖耐受性，因此很可能有超过10%的后代具有乳糖耐受性。” 这个数字有多强大？从人类遗传学的角度看看这种特性会传播得多快——个体会变成群体，而且他们有10%的遗传优势。数学分析表明，仅在100代人之后，95%的人口都会有这种特性。 对于人类来说，实现这种进步需要的时间连2000年都不到。“人们经常问我一个问题：人类是否还在进化？我的回答总是：当然啦。”