NPR 07-20:Atomic Tune-Up: How the Body Rejuvenates Itself人类能

The human body replaces 98 percent of its atoms yearly, but the makeover prompts wider questions.

From NPR news, this is All Things Considered. I am Debbie Elliott. Time now for our look at some of the elemental questions of life in our segment Science Out of the Box.

Many have heard someone say I am not the person I was. Well, that maybe more true than you know. NPR science correspondent David Kestenbaum has this tale.

Okay, we all get haircuts, but have you ever thought that when we do, we lose atoms. That hair that was once part of us goes its own way. So, um, at the end of the day, what happens to my hair on the floor here?

Well, they will get swept up and put into the trash.

Those are my atoms.

How much of me is really with me throughout my life? Mean my skin rubs off. I trim my fingernails. Part of me is eroding¹, and presumably being rebuilt, but how much is it? One percent? Is it ten percent? I called around to biologists and chemists and no one seemed to know the answer.

I'm Logan McCarty. I teach chemistry at Harvard University.

Had you ever thought about, to what extent, we're just spare parts being replaced all the time?

I guess it never really occurred to me. You know, who I was is not, the atoms that I have now are not the same atoms that I had, you know, yesterday or the week before.

McCarty did some research. And he found this article from a Smithsonian Institution Publication from 1953. So this is the beginning of the atomic age and the article described the six experiments where researchers fed people radioactive atoms or they injected them with radioactive atoms and then using radiation detectors² they could watch the atoms as they moved around. So they watched them go up one arm into the heart and down the other arm.

You can follow it through their body. Does it get excreted through urine or is it excreted through their sweat or through feces or, you know, what happens to it, does it end up in their fingernails or in their eyeballs or, you know, so you can follow where these atoms go.

And where do they (go)?

And by doing that. Well, they end up in, in all of your tissues.

A lot of the atoms get incorporated into our bodies. The article says the atomic turnover³ is quite rapid and quite complete.

In a year, 98% of the atoms in us now will be replaced by other atoms that we take in, in our air, food and drink. So that means 98% of me is new every year. So this is the very profound rule of nature: you are what you eat.

Yes, absolutely. If you eat a hamburger one day, then the atoms and molecules⁴ in that hamburger will end up making up your cell walls, and different organs and tissues.

So my friend, I have a friend of friend who eats soup everyday for lunch. So he is mostly made up of soup or largely.

He is mostly made up of soup, yes.

But don't be sad. McCarty says this constant replacement⁵ of parts is actually what makes life so robust⁶ and so adaptable⁷, so so lively.

Life is remarkable⁸ in that it requires always a flow of energy and matter through the system. So that if the system isn't constantly bringing in new energy, and bringing in new matter then it is basically dead.

Still, this means that in a very real sense, we are not the people that we were a year ago with this collection of atoms that hang out together for a while and they go on to do other things sort of a momentary⁹ crowd of organization. So what is me? Am I still me if my parts have been replaced?

Well, of course, the, the question goes way back to ancient philosophy.

This is Daniel Dennett. He is a philosopher at Tufts University.

Remember he says the old joke about Abe Lincoln's axe¹⁰.

There it is, in the glass case. And it says This is Abe Lincoln's axe. Someone says is that really his axe. He says, Oh, yes. But of course, the head has been replaced twice and the handle three times.

There is also a modern atomic version of this puzzle. That really gets to the heart of things.

We imagine that, your rocketship has landed on Mars. You have to get back from Mars to Earth by teleporter.

Here is how the teleporter works. It dismantles¹¹ you atom by atom, deluuuu, you know. Records the precise location, every carbon, every hydrogen every phosphors. And it sends that information to earth. Uuuu where receiving transporter reconstructs you, blurrrrrrrr out of new atoms.

And you step out of the teleporter receiver on Earth. Is that really you? I say of course it's you.

Okay! That is clear enough. But now imagine he says instead the teleporter on Mars doesn't take your parted, doesn't disassemble you. It just scans your atom, dudududud. Leaving you intact.

So now you are, there is a you that's stranded¹² on Mars. And there is a you that's back on Earth, which is the really you.

Well, it's pretty clear to me. Then there is, then I have David One and David Two.

Yeah, and, and, and does one of them have some sort of special priority, is one of them sort of realer, more you than the other.

Then what does my wife do?

Exactly, yes.

I can tell you what my wife would do. My wife would groan¹³ if two of me showed up.

It turns out there are some atoms that are with us for our entire lives. This comes from a research in Sweden. And the atoms are actually in some interesting places. They are deep in the DNA¹⁴, of some cells in our brain and in our heart and also some atoms in our teeth. So brain, heart and teeth. Don't forget to brush.

That is the temporary collection of atoms currently known as our science correspondent David Kestenbaum.

1 eroding   

侵蚀，腐蚀( erode的现在分词 )； 逐渐毁坏，削弱，损害

参考例句：

• The coast is slowly eroding. 海岸正慢慢地被侵蚀。
• Another new development is eroding the age-old stereotype of the male warrior. 另一个新现象是，久已形成的男人皆武士的形象正逐渐消失。

2 detectors   

探测器( detector的名词复数 )

参考例句：

• The report advocated that all buildings be fitted with smoke detectors. 报告主张所有的建筑物都应安装烟火探测器。
• This is heady wine for experimenters using these neutrino detectors. 对于使用中微子探测器的实验工作者，这是令人兴奋的美酒。 来自英汉非文学 - 科技

3 turnover   

n.人员流动率，人事变动率；营业额，成交量

参考例句：

• The store greatly reduced the prices to make a quick turnover.这家商店实行大减价以迅速周转资金。
• Our turnover actually increased last year.去年我们的营业额竟然增加了。

4 molecules   

分子( molecule的名词复数 )

参考例句：

• The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
• Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。

5 replacement   

n.取代，替换，交换；替代品，代用品

参考例句：

• We are hard put to find a replacement for our assistant.我们很难找到一个人来代替我们的助手。
• They put all the students through the replacement examination.他们让所有的学生参加分班考试。

6 robust   

adj.强壮的，强健的，粗野的，需要体力的，浓的

参考例句：

• She is too tall and robust.她个子太高，身体太壮。
• China wants to keep growth robust to reduce poverty and avoid job losses,AP commented.美联社评论道，中国希望保持经济强势增长，以减少贫困和失业状况。

7 adaptable   

adj.能适应的，适应性强的，可改编的

参考例句：

• He is an adaptable man and will soon learn the new work.他是个适应性很强的人，很快就将学会这种工作。
• The soil is adaptable to the growth of peanuts.这土壤适宜于花生的生长。

8 remarkable   

adj.显著的，异常的，非凡的，值得注意的

参考例句：

• She has made remarkable headway in her writing skills.她在写作技巧方面有了长足进步。
• These cars are remarkable for the quietness of their engines.这些汽车因发动机没有噪音而不同凡响。

9 momentary   

adj.片刻的，瞬息的；短暂的

参考例句：

• We are in momentary expectation of the arrival of you.我们无时无刻不在盼望你的到来。
• I caught a momentary glimpse of them.我瞥了他们一眼。

10 axe   

n.斧子；v.用斧头砍，削减

参考例句：

• Be careful with that sharp axe.那把斧子很锋利，你要当心。
• The edge of this axe has turned.这把斧子卷了刃了。

11 dismantles   

拆开( dismantle的第三人称单数 )； 拆卸； 废除； 取消

参考例句：

• This toy machine gun dismantles easily. 这种玩具机关枪很容易拆卸。
• By contrast, modern scepticism challenges nobody and dismantles only theories of change. 相反，现代的怀疑主义却并不质疑任何人，仅仅摧毁变革理论。

12 stranded   

a.搁浅的，进退两难的

参考例句：

• He was stranded in a strange city without money. 他流落在一个陌生的城市里， 身无分文，一筹莫展。
• I was stranded in the strange town without money or friends. 我困在那陌生的城市，既没有钱，又没有朋友。

13 groan   

vi./n.呻吟，抱怨；(发出)呻吟般的声音

参考例句：

• The wounded man uttered a groan.那个受伤的人发出呻吟。
• The people groan under the burden of taxes.人民在重税下痛苦呻吟。

14 DNA   

(缩)deoxyribonucleic acid 脱氧核糖核酸

参考例句：

• DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
• Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。