美国国家公共电台 NPR--When did human bodies evolve to sweat? We don't know exactly when

When did human bodies evolve to sweat? We don't know exactly when

Transcript¹

All summer, NPR's Science Desk has been looking at sweat. Humans are covered with millions of sweat glands², but it wasn't always that way. When did humans start to sweat?

RACHEL MARTIN, HOST:

All summer, NPR's science desk has been looking at sweat. Humans are covered head to toe with millions of sweat glands. But it wasn't always so. NPR's Pien Huang tells us how human bodies evolved so we could sweat.

PIEN HUANG, BYLINE³: Sweating is essential to humans.

HEATHER DINGWALL: During the heat wave, I was sweating just, like, walking to work. And I think it probably kept me alive (laughter).

HUANG: That's Heather Dingwall, a human evolutionary⁴ biologist. And she was walking to her job as a postdoc at UPenn. There she studies organs in the skin, like hair follicles and, of course, sweat glands. Sweat glands are actually coiled tubes that bring water from inside your body to the surface.

DINGWALL: You're effectively moving the heat from your body to that water droplet⁵.

HUANG: As the water droplet evaporates, it takes the heat off your skin. Now, a lot of animals don't sweat, but humans do. And we don't know exactly when it started. There's no fossil record of ancient sweat glands because the soft tissue of the skin falls apart. But Dingwall says it's an adaptation that likely came around a long time ago.

DINGWALL: Probably around the time when the environment was getting drier and warmer. And so that would be around, like, 1 1/2 to 2 1/2 million years ago.

HUANG: This was in East Africa, where modern humans emerged. Before then, early humans lived in the cool shade of the forest. They had short bodies covered in thick hair to stay warm. Then the climate and landscape changed. Grasslands⁶ replaced forests. And humans spent a lot more time in the sun, where they had the opposite problem. They needed to stay cool. So having a body covered in sweat glands became an advantage.

DINGWALL: So you might be able to forage⁷ for longer, hunt for longer, collect more food. Or even if it's just - it could be as simple as, like, not dying of heat stroke.

HUANG: Whatever benefits humans got from sweat must have been huge because sweating requires you to keep drinking lots of water.

DINGWALL: And if you lose too much water, then you become dehydrated. And also, you will die.

HUANG: Humans, of course, haven't died off. Instead, we've thrived thanks to our sweat. It's core to who we are, even more so than our giant brains, which evolved much later. There's nothing more human than being sweaty.

Pien Huang, NPR News.

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1 transcript   

n.抄本，誊本，副本，肄业证书

参考例句：

• A transcript of the tapes was presented as evidence in court.一份录音带的文字本作为证据被呈交法庭。
• They wouldn't let me have a transcript of the interview.他们拒绝给我一份采访的文字整理稿。

2 glands   

n.腺( gland的名词复数 )

参考例句：

• a snake's poison glands 蛇的毒腺
• the sebaceous glands in the skin 皮脂腺

3 byline   

n.署名；v.署名

参考例句：

• His byline was absent as well.他的署名也不见了。
• We wish to thank the author of this article which carries no byline.我们要感谢这篇文章的那位没有署名的作者。

4 evolutionary   

adj.进化的；演化的，演变的；[生]进化论的

参考例句：

• 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。

5 droplet   

n.小滴，飞沫

参考例句：

• The rate of droplet growth under different conditions can be evaluated.可以计算在不同条件下的云滴增长率。
• The test results showed that increasing droplet size was associated with better stability.试验结果表明，增加液滴尺寸将使稳定性提高。

6 grasslands   

n.草原，牧场( grassland的名词复数 )

参考例句：

• Songs were heard ringing loud and clear over the grasslands. 草原上扬起清亮激越的歌声。 来自《现代汉英综合大词典》
• Grasslands have been broken and planted to wheat. 草原已经开垦出来，种上了小麦。 来自《简明英汉词典》

7 forage   

n.(牛马的)饲料，粮草；v.搜寻，翻寻

参考例句：

• They were forced to forage for clothing and fuel.他们不得不去寻找衣服和燃料。
• Now the nutritive value of the forage is reduced.此时牧草的营养价值也下降了。