2.High School English Listening

What makes the human brain so special? Actually, it mightnot be that special after all.
In 2009, Dr. Suzana Herculano Houzel and her colleagues showed that the human brain has thesame density of nerve cells as other primates. Comparing humans to smaller primates, she claimsthat our brain is no bigger than it should be for our body size. Still, given the distinctive way thatprimate brains scale with size, we may have the most brain cells of any mammal.
That being said, gorillas can grow to be three times our size, but still have much smaller brains thanours.
Brain cells need more energy than most body cells. Although the brain is less than 2 percent of themass of the human body, it consumes 20 percent of our resting metabolic energy. Gorillas haveto spend more than eight hours every day eating to get enough calories to support their bigbody, and they simply can't afford a bigger brain.
So, then, how did human ancestors overcome this limitation? Beginning with homo erectus, abouttwo million years ago, our ancestors couldn't have afforded the metabolic cost of their increasinglylarge brains if they ate raw food like gorillas do.
Primatologist Richard Wrangham thinks that the invention of cooking with fire is what made thisgrowth in brain size possible. Cooked food is easier to digest and yields more calories. Cooking mayhave made the human brain possible, and freed us from having to spend all day eating.
译文：
是什么让人类的大脑如此特别？事实上，它可能并不那么特别。
2009年，苏珊娜-赫库拉诺-霍泽尔博士和她的同事表明，人类的大脑具有与其他灵长类动物相同的神经细胞密度。将人类与较小的灵长类动物相比较，她声称我们的大脑并没有比我们的身体大小所应该有的大。尽管如此，考虑到灵长类动物的大脑随体型变化而变化的独特方式，我们可能拥有所有哺乳动物中最多的脑细胞。
也就是说，大猩猩可以长到我们体型的三倍，但其大脑仍然比我们小得多。
脑细胞比大多数身体细胞需要更多的能量。尽管大脑不到人体重量的2%，但它消耗了我们静止代谢能量的20%。大猩猩每天必须花8个小时以上的时间进食，以获得足够的热量来支持其庞大的身体，而它们根本无法负担更大的大脑。
那么，人类的祖先是如何克服这一限制的呢？从大约200万年前的直立人开始，如果我们的祖先像大猩猩那样吃生的食物，他们就无法承担越来越大的大脑的代谢成本。
灵长类动物学家理查德-维兰厄姆认为，用火做饭的发明使大脑尺寸的增长成为可能。煮熟的食物更容易消化，产生更多的卡路里。烹饪可能使人类的大脑成为可能，并使我们不必整天都在吃饭。
重点词汇：
human brain 人脑
after all 毕竟 ; 居然 ; 终究 ; 竟然;居然
primates 灵长类 ; 灵长目动物 ; 大主教 ; 总主教 ; primate的复数
be for 到…去，赞成
body size 体格大小
of any 在所有的…当中
gorillas 大猩猩 ; 高大凶恶的人 ; gorilla的复数
less than 少于 ; 毫不 ; 完全不 ; 一点都不
human body 人体
metabolic energy 代谢能