英语听力跟读训练材料

英语听力跟读训练材料

Cooking Up Human Intelligence

So what makes the human brain so special? Actually, it might not be that special after all.

Sliding Scales

In 2009, Dr. Suzana Herculano Houzel and her colleagues showed that the human brain has the same density of nerve

cells as other primates. Comparing humans to smaller primates, she claims that our brain is no bigger than it should be for our body size. Still, given the distinctive way that primate 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 than ours.

Brain cells need more energy than most body cells. Although the brain is less than 2 percent of the mass of the human body, it consumes 20 percent of our resting metabolic energy. Gorillas have to spend more than eight hours every

day eating to get enough calories to support their big body, and they simply can’t afford a bigger brain.

Brain Food

So, then, how did human ancestors overcome this

limitation? Beginning with homo erectus, about two million years ago, our ancestors couldn’t have afforded the

metabolic cost of their increasingly large brains if they ate raw food like gorillas do.

Primatologist Richard Wrangham thinks that the invention of cooking with fire is what made this growth in brain size possible. Cooked food is easier to digest and yields more calories. Cooking may have made the human brain possible, and freed us from having to spend all day eating.

density n. 密度

distinctive adj. 有特色的，与众不同的

mammal n. [脊椎] 哺乳动物

metabolic adj. 变化的；新陈代谢的

n. 灵长类动物学家 (primatology的变形)

烹饪与人类的智慧

所以说是什么让人类的大脑如此特别？实际上，这或许根本就不特别。

变化的幅度

在2009年，苏珊娜·埃尔库拉诺·乌泽尔博士和她的同事们展示了人类大脑的神经细胞密度和其它的灵长类动物一样。与其它较小的灵长类动物相比，苏珊娜博士称我们的大脑与我们自身体型相比并不算大。但考虑到灵长类动物大脑尺寸比例的独特方式，人类拥有所有哺乳动物中最多的脑细胞。

话虽如此，大猩猩能长到我们体型的三倍，但它们的大脑仍然比我们小得多。

脑细胞比其它身体细胞需要更多的能量。虽然大脑所占人体的比重小于2%，但它却消耗我们静止时代谢能的20%。为了给庞大的身躯提供充足的能量，大猩猩每天要花费超过8小时的时间进食，所以它们无法负担更大的大脑。

大脑的食物

所以，人类的祖先又是如何突破限制的？从直立的人类开始，大约两百万年前，随着大脑越来越大，如果人类的祖先还像大猩猩那样进食生的食物，那么他们将无法给大脑提供充足的代谢值。

灵长类动物学家理查德·兰厄姆认为发明用火烹饪，使得大脑生长变大成为可能。烹煮的食物更容易消化并且能产生更多的热量。烹饪或许促动了人脑的形成，并将人类从整日进食的境况中解放出来。