“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.”
【視聽版科學(xué)小組榮譽出品】
complex sugar evolutionary importance remarkable reproductive advantage mathematical analysis
“實際上，對于小孩子和成年人來講，當(dāng)身體內(nèi)表達一種叫乳糖酶的蛋白時，他們才能消化牛奶?！?二月二十日，在華盛頓的美國科學(xué)發(fā)展協(xié)會會議上，談起過去9000年來不同人身體中乳糖耐受性的最新進化，賓夕法尼亞州大學(xué)的薩拉?特斯科夫這樣說道?！安槐磉_這種酶的人不能消化這種復(fù)糖?！?我們可以用數(shù)字來衡量乳糖耐受性在進化史上的重要程度嗎？“選擇壓力非常顯著。實際上我們預(yù)測有10%的人具有乳糖耐受性，因此很可能有超過10%的后代具有乳糖耐受性?！?這個數(shù)字有多強大？從人類遺傳學(xué)的角度看看這種特性會傳播得多快——個體會變成群體，而且他們有10%的遺傳優(yōu)勢。數(shù)學(xué)分析表明，僅在100代人之后，95%的人口都會有這種特性。 對于人類來說，實現(xiàn)這種進步需要的時間連2000年都不到。“人們經(jīng)常問我一個問題：人類是否還在進化？我的回答總是：當(dāng)然啦?！?/div>