Why Am I Left-Handed?

我第一次遇到对左撇子的偏见是在高中拉丁语课上。

The very first time I encountered a bias against left handed people was in my high school Latin class.

在那里我学到，拉丁语中表示右的词是dexter，英语中的dexterity（灵巧）就来源于此，用来形容手巧的人；而拉丁语中表示左的词是sinister，也就是英语中的sinister，意思是邪恶、有害或犯罪。

There I learned that the Latin word for right is dexter, in which we get the English words dexterity and to describe someone good with their hands, while the Latin word for left is sinister, or as we say in English, sinister, meaning harmful, evil, or criminal.

需要说明的是，显然没有任何道德依据可以因为一个人的惯用手而歧视他们，但这种古老的偏见仍然体现在我们的语言中，反映了我们物种内部更深层的数字偏见，这种偏见似乎在某种程度上由进化机制维持着。

To be clear, there's obviously no moral basis for discriminating against anyone based on their handedness, but this ancient societal bias still captured in our language reflects a deeper numerical bias within our species, one that seems to be maintained at some level by the mechanisms of evolution.

欢迎收听Quanta播客，我们在这里探索基础科学和数学的前沿。

Welcome to the Quanta Podcast, where we explore the frontiers of fundamental science and math.

我是Hannah Waters，Quanta杂志的高级编辑。

I'm Hannah Waters, the senior editor at Quanta Magazine.

今天我们知道，每十个人中就有一个是左撇子，这意味着剩下的90%的人都是右撇子。

Today, we know that one out of every 10 people is left handed, which means the remaining 90% of us lean to the right.

这种统计上的不平衡很不寻常。

This statistical imbalance is unusual.

比如，狗可能是左爪或右爪，但在整个狗群体中并没有这种数量上的偏好。

Dogs, for example, can be left or right pawed, but there's no numerical preference across the population of dogs.

为什么进化会维持人类这种九比一的左右手比例呢？

Why would evolution maintain a ninety ten split in humans?

而且，为什么我们一开始就会偏好某一只手呢？

And why do we have a preference for one hand or the other in the first place?

幸好我们有一位好奇的左撇子科学记者来帮我们探索这些问题。

Thank goodness we have a curious left handed science journalist on hand to explore such questions for us.

《量子》杂志的资深撰稿人娜塔莉·沃尔乔弗在她最近的专栏《我为什么是左撇子？》中，深入探讨了科学和自我发现的问题。

Longtime Quanta writer Natalie Wolchover went down a rabbit hole of scientific and self discovery in her recent column, Why Am I Left Handed?

娜塔莉，欢迎回到节目。

Natalie, welcome back to the show.

很高兴来到这里，汉娜。

Nice to be here, Hannah.

那么，这里的大问题是什么？

So what's the big idea here?

大问题其实是，尽管我们每个人在生活中都体验过自己的用手习惯，但我们仍然不明白为什么人类会有这种九比一的右撇子左撇子比例，这真的很了不起。

The big idea is really that it's remarkable that we still don't understand why there's this ninety ten right handed, left handed split in humans despite it being something that we all experience in our lives, our handedness.

不过，确实有一些很有意思的新进展可以聊聊。

And yet there are some really interesting new developments to talk about.

那你是什么时候第一次意识到自己跟别人不一样，就是

So when did you first realize that you were different, that

你是左撇子？

you were left handed?

我不记得自己什么时候意识到的，因为那可能是在我记事之前。

I don't remember when I first was aware of it because it would have been pre memory formation.

你知道吗，我在报道中了解到，我们的惯用手在出生前就决定了。

You know, one thing I learned in my reporting was that our handedness is determined before birth.

你出生时就已经偏向用一只手了，比如吸手指，我就是这样。

You kinda come out already favoring one hand for things like thumb sucking, which I did do.

所以我能回想起来，我吸的是左手拇指。

So I can think back and remember that it was my left thumb that I sucked.

顺便说一句，我吸的是右手。

Mine was my right, for the record.

对，没错。

Checks out.

那你作为左撇子长大的经历是怎样的，在一个

And what was your experience coming up as a lefty in a

右撇子的世界里？

right handed world?

我记得我一开始是镜像书写的。

I remember that I initially did mirror writing.

我会用左手从右往左写，基本上是模仿右撇子笔迹的镜像动作。

So I would write from right to left using my left hand, basically mirroring the strokes of a right handed penman.

用左手做同样的手部动作，写出来的字就是镜像的。

Doing the same hand motions produces mirror image writing if you're using your left hand.

所以我得特别努力才能记住要从左往右写。

And so I had to really work to remember to go from left to right.

而且很多时候，即使我已经写得很流利了，我还是会偶尔不小心把自己的名字写反，甚至故意把句子写反，因为对左撇子来说，从右往左写其实感觉更自然。

And a lot of the time, even extending into when I could write very fluently, I would still sometimes accidentally write my name the wrong way or even purposely write my sentences the wrong way because it actually feels more natural to a lefty to write from right to left.

有趣的是，我女儿也是左撇子，虽然我们其实没有血缘关系，但她也是左撇子，而且她也有同样的习惯。

And the interesting thing is my daughter who's left handed, and we're actually not biologically related, but she's left handed and she does the same thing.

她也会镜像写字，有时候会忘记，还是会从右往左写自己的名字。

She mirror rights and forgets sometimes and still writes her name from right to left.

所以我发现，这其实是很多孩子都会有的经历。

So I've realized that's actually quite a common experience for kids.

而且作为左撇子，你知道，小时候确实会遇到一些麻烦。

And then also as a lefty, you know, you have these struggles as a kid.

你会有点显得与众不同。

You're the odd one out a little bit.

你得学会用右手剪刀，用起来不太顺手。

You have to learn to use right handed scissors, and it's not totally natural.

小时候的课桌通常右边有个放手的地方，所以对你来说不太合适。

Desks when you're a kid often have a place to lean your arm on the right side, so, you know, it doesn't suit you quite right.

所以左撇子要面对不少小麻烦，但都挺小的，你也就慢慢习惯了。

So there's various things you have to deal with from being left handed, but it's quite minor and you just move past it.

某种程度上，你会开始意识到，左撇子可能还真有点奇怪的优势。

And in a way, you start becoming aware of how there might actually be some kind of strange advantage to being

左撇子。

a lefty.

我是在一个棒球家庭长大的。

I grew up in a baseball family.

所以很早就知道，左撇子投手其实有点优势，因为他们能让人心理上有点发怵，或者他们在运动上和身体上跟右撇子选手不一样。

And so learning very early on, the left handed pitchers actually have a bit of an advantage because they can kinda psych out or they are athletically and physically different than the right hander

选手。

players.

对。

Yeah.

完全同意。

Totally.

而且，左撇子击球手也有优势，我记得打垒球的时候，球员站在另一边会让投手有点困惑。

And also, left handed batters have an advantage, and I remember that from playing softball that it confuses a pitcher a little bit when the player's on the other side.

对。

Yeah.

然后我读到，比如吉米·亨德里克斯，显然，他可能是史上最伟大的吉他手之一，而他是左撇子。

And then I was reading, like, Jimi Hendrix, apparently, one of the probably the best guitarists of all time was left handed.

你觉得左撇子群体在某些方面表现特别出色，这该怎么解释呢？

What do you attribute this kind of exceptionalism in some respects within the left handed community?

这确实是谜团的一部分。

That is certainly a part of the mystery.

因为我们还不完全了解左撇子与大脑神经活动异常模式之间的各种关联，所以目前还不清楚为什么左撇子在某些领域特别擅长。

Because we don't understand left handedness in all of the ways that it's related to other kinds of abnormal patterns of neuronal activity, we don't really understand yet why there are certain fields that lefties excel in.

体育方面就比较明显了。

The sports one is more obvious.

在徒手搏斗、球拍运动或竞技体育中，如果你是左撇子，就有一种出其不意的效果。

There's an element of surprise when you're a lefty in hand to hand combat or any racket sports or competitive sports.

当你从左侧进攻时，人们对这类身体动作会稍微不熟悉一些。

If you're coming at things from the left side, people are just slightly less familiar with those kinds of physical motions.

所以左撇子是有优势的。

And so lefties have an advantage.

比如说，你在篮球队里，有一个左撇子球员，能在球场左侧运球运得很好，那是个优势。

And then say you're, you know, on a basketball team, it's an advantage to have a player who's a lefty who can dribble really well down the left side of the court.

而且，我们稍后会在对话中谈到，这跟一个关于为什么会有左撇子、为什么不是百分之百右撇子而是九比一的比例的理论有关。

And as we'll get into later in our conversation, that's related to one of the theories about why there is any left handedness at all, why it's not a 100 bias instead of ninety ten.

你

Have you

是不是一直对这个问题很感兴趣？

been interested in this question for a long time?

你是什么时候开始把它当作一个科学问题，觉得自己可以以科学记者的身份去研究的？

When did you think of it as a scientific question that you could pursue as a science journalist?

是的。

Yeah.

我确实一直很感兴趣。

I have really been interested in it.

你知道，我有机会为《Quanta》写这些精彩的随笔，在那里我可以纯粹地追随自己对某个话题的好奇心。

You know, I get to do these wonderful essays for Quanta where I just pursue my curiosity on a subject.

所以，我之所以受到启发去深入研究这个问题，是因为今年早些时候发表的一篇论文引起了我的注意。

And so I was inspired to look into this more because of a paper that was published earlier this year that caught my eye.

那篇论文触及了这个非常复杂问题的一个方面，而这个问题实际上跨越了许多不同的科学领域。

And that paper was getting at one aspect of this very complicated question, which actually spans many different scientific fields.

在了解那项研究的过程中，我想，让我试着看看我们在破解这个谜团上到底取得了多少进展。

And just in learning about that research, I thought, let me try to actually see how far we've come in cracking this mystery.

那么，惯用手

So what does

意味着什么呢？

it mean to have handedness?

在更深的生物学或科学层面上，你学到了什么？

What have you learned at a kind of deeper biological or scientific level?

好的。

Okay.

在大脑里，有一种叫做大脑偏侧化的模式，就是大脑把任务分给左右两边。

So in the brain, there's these patterns of brain lateralization, it's called, where the brain divides tasks between left and right.

我们大脑的右侧控制着身体右侧的肌肉和神经，而大脑的左侧控制着身体左侧。

And we control our muscles and nerves on the right side and the left side of our brain, and we control the left sides of our bodies in the right side of our brain.

所以如果你是左撇子，那意味着你大脑右侧的运动回路连接更紧密、更丰富。

So if your left hand is dominant, it really means that circuitry that's on the right, the motor circuitry, is more interconnected and richer.

可能神经元更多，但肯定是控制你左手的那部分神经元连接更紧密。

Maybe more neurons, but certainly more interconnected neurons that are controlling your left hand.

而右撇子的话，情况就正好相反。

And then in a right handed person, it would be the opposite.

他们大脑左侧控制右手的那部分，神经连接会更丰富。

Their left side of their brain controlling their right hand would be richer neurally.

所以作为右撇子，我

So I have

的左脑连接更紧密。

a more interconnected left brain as a right handed person.

对。

Yeah.

有趣的是，我们的双手本身是完全一样的。

One of the interesting things about it is our hands themselves are identical.

比如，你看看自己的手，真的分不清左右。

Like, you look at your hands and you really cannot tell them apart.

所以这其实跟手本身没什么关系。

So it's not really to do with what's going on in our hands.

关键在大脑。

It's about our brains.

那在发育过程中，左右撇子是什么时候决定的呢？

And when during development is that handedness decided?

这是

So this was one

我了解到的最有趣、最令人惊讶的事实之一。

of the most interesting and surprising facts that I learned.

几十年前有一系列超声波研究，显示胎儿在妊娠很早的阶段就开始更多地活动一只手臂。

There was a series of ultrasound studies decades ago at this point that showed that fetuses are actually moving one arm more than the other from a pretty early point in gestation.

大约在受孕后十周，胎儿那时只有芸豆那么大，非常小，但已经明显更多地活动一只手臂了。

Around ten weeks post conception, the fetus, which at that point is like the size of a kidney bean, just really tiny, is moving one arm much more than the other.

这些研究观察胎儿的手臂活动，然后追踪这些婴儿后来的惯用手，结果发现两者高度相关。

And there are these studies that look at arm motions of the fetus and then check what the handedness of that baby is later and it correlates very strongly.

所以，孕期哪只手臂动得多，确实和后来哪只手更灵活密切相关。

So which arm is moving more during gestation really correlates with which hand is dominant later on.

这显然是个重要线索。

That's obviously a big clue here.

我找到一项2017年的研究，还和其中一位作者聊过，研究发现脊髓左右两侧的基因表达存在不对称性，这可能是导致胎儿一侧身体活动更多的原因。

There was this 2017 study I came across and then spoke with one of the authors about that showed that there's a lot of gene expression asymmetry between the left and right sides of the spinal cord that are potentially causing that difference where one side is much more physically active, so one side of the fetus is moving more.

这种不对称的基因表达，也就是左右两侧不同的基因被激活并合成蛋白质，就发生在脊髓的那个阶段。

So this asymmetric gene expression, so different genes being turned on and building proteins on the left and right, is happening at that point in the spinal cord.

而这实际上就是导致一只手占主导地位的原因。

And that's what actually seems to lead to one hand being dominant.

有趣的是，这一切都发生在大脑真正控制这些手臂动作之前。

And fascinatingly, that's happening all before the brain is actually controlling those arm motions.

所以这真的只是胎儿在做的无意识动作。

So it's really just involuntary motions that this fetus is making.

直到后来，大脑才连接到运动回路，并开始参与其中。

And then only later is their brain hooking up to their motor circuitry and then getting involved.

所以这是一个重要的线索。

So a big clue.

我和那项研究的作者塞巴斯蒂安·奥赫伦贝格聊过，他是汉堡医学院的，他的解释是，其实我们的利手性是由脊髓先确定的，然后才导致大脑的不对称。

I spoke to the author of that study, Sebastian Ochlenberg of the medical school in Hamburg, and his interpretation is that it's actually our handedness that's already established by the spinal cord that then leads to the asymmetry in our brain.

因为一只手臂比另一只动得多，当大脑连接到身体时，由于反馈，它会为那一侧分配更多的神经回路。

So because the one arm is moving more than the other, the brain, when it does hook up to our bodies, is then devoting more neurocircuitry to that side because of feedback.

然后这种不对称性就传递到了大脑。

Then that asymmetry is cascading to the brain.

从那时起，大脑就开始负责控制手的动作了。

And then from that point on, the brain is then in charge of controlling the motions of the hand.

所以，是的，实际上是我们的手在决定大脑里发生什么。

So, yeah, it's our hands actually dictating what happens in our brains.

如果到十周时这已经形成了，生物学家就会问，那这又是怎么被设定的呢？

If by ten weeks, it seems like this has already developed, the biologist then asks, so then how does that get set?

你之前提到过基因表达。

You mentioned gene expression earlier.

你有没有找到某些与左撇子相关的特定基因？

Are there certain genes that you were able to find that are associated with left handedness?

在更深层次上，是什么在编程这个？

What's programming this at a deeper level?

对。

Yeah.

所以最近有一些大规模的研究。

So very recently, there have been these large studies.

现在很多人都会做基因组测序，而且这很容易做到。

Now that so many people get their genome sequenced and that's easy to do.

终于有这些研究发现了某些基因和左撇子之间的关联。

There are finally these studies that are finding associations between certain genes and left handedness.

以前人们以为可能只有一个左撇子基因或者一个手性基因。

It was thought back in the day that there might be like one left handedness gene or one handedness gene.

但事实显然不是这样。

And that's certainly not the case.

不过大约有40个基因被确认，如果你有这些基因，数量越多，成为左撇子的几率就越高。

But there are around 40 genes that have been identified as if you have them, the more of them you have, the higher chance of being a lefty you have.

所有这些基因都属于一个叫做微管蛋白基因的家族。

And all of these genes are in this family called tubulin genes.

它们在形成细胞的结构成分方面非常重要，它们构成了细胞中叫做微管的部分的基础。

They are very important in forming structural components of cells, so they form the building blocks of these parts of cells called microtubules.

所以这个发现——关于微管蛋白基因，某些基因变异会导致左撇子——对研究这个的科学家来说完全出乎意料。

And so this discovery that it's about tubulin genes, that certain variants of these genes would lead to left handedness, was totally surprising to scientists who study this.

这只是在最近几年才变得清晰，显然这是理解背后机制的重要线索。

It's only in really in the past few years that this has become clear, and it's obviously a huge clue to what's going on.

微管居然能预测左撇子，这对我来说也太意外了。

The idea that microtubules can somehow predict left handedness is surprising to me too.

它们构成了细胞的骨架，还能把物质从细胞的一部分运到另一部分。

They make up a cell's skeleton, and they can transport things from one part of a cell to another.

那这跟左撇子有什么关系呢？

Why would that have anything to do with handedness?

我觉得现在还不清楚。

I think it's unclear.

我们能推测的是，微管可能发生了某种变化，影响了脊髓中运动神经回路的发育。

What we can speculate about is that something about the microtubules is changing in a way that affects the motor circuitry development in the spinal cord.

所以可能发生的情况是，某些信号分子在细胞内的运输方式，也许因为微管结构的某种改变，最终集中在了细胞的一部分，而不是另一部分。

So what could be happening is that the way that certain signaling molecules are being transported around the cell, maybe because of some switch to the structure of the microtubules, they're ending up concentrated in one part of a cell as opposed to another.

然后经过细胞分裂，这就变成了细胞之间的差异。

And then after cell division, this turns into a difference between cells.

所以最终你会得到两个截然不同的细胞群体，而这种差异源于微管结构改变带来的方向性差异。

So you end up getting two populations of cells that are quite different and that it is originating between this directional difference that's starting with microtubules changing in structure.

所以我觉得，既然他们已经发现了这些微管蛋白基因，未来几年甚至几十年，研究都会集中在这个领域，但我们还不完全清楚在怀孕早期那几周里，这一切到底是怎么发生的。

So I think this is the area in which research will be happening over the next years and decades now that they've identified these tubulin genes, but we don't exactly know yet how it's all happening in those early weeks of gestation.

所以，当我想到生物学时，我觉得它分为两个部分。

So when I think about biology, I think about it having two parts.

一个是物理层面的解释，可能就是这套微管系统决定了你是左撇子还是右撇子。

One is the physical explanation, which is potentially this microtubule system that creates left handedness or right handedness.

另一个是生物学的历史或进化层面，那就是为什么会有左撇子，而且比例一直保持在九比一，也就是每九个右撇子就有一个左撇子？

Then there's also a historical or evolutionary part of biology, which is why have left handedness at all and in this consistent ratio of one to nine, one lefty to every nine righties?

你有没有找到关于这种偏好的进化解释？

Have you been able to uncover an evolutionary explanation for this bias?

有。

Yeah.

另外，在我们完全离开遗传学这个话题之前，我想说，关于左撇子，有一个重要且有趣的现象，就是它确实有遗传成分，但同时也带有一定的随机性。

And I should say also before we move totally on from genetics, an important and fascinating thing about left handedness is there is a genetic component, but it's also somewhat random as well.

所以，如果父母都是左撇子，他们生出左撇子孩子的概率其实也只有四分之一左右。

So if there's two parents who are left handed, the chance that they'll have a left handed kid is still only like a quarter.

甚至同卵双胞胎，一个会是左撇子，另一个会是右撇子。

And even identical twins, one will be a lefty and the other will be right handed.

所以就是说，这些微管蛋白基因确实有关系，但也有一些随机性在起作用。

So it's like, okay, these tubulin genes are involved, but there's also some randomness involved.

这说明，不管是什么过程决定了惯用手，它都非常微妙，可能偏向任何一边。

So that tells you that whatever the process is that's creating handedness, it's very subtle and could go either way.

所以，从进化的角度来说，为什么会有这种轻微的偏向，大多数时候让胎儿成为右撇子，但有时又让它成为左撇子，这是这个谜团的另一个迷人之处。

So in terms of why evolution would put in that slight bias that most of the time pushes the fetus to being right handed but sometimes pushes it left handed is another fascinating aspect of the mystery.

这个领域里的大多数猜测和研究，都在试图搞清楚，为什么人类会稳定地保持这种九比一的比例。

Most of the speculation in this field and most of the research is trying to grapple with why would this be a stable and preferred state for humanity to have this ninety ten.

你知道，这在其他身体特征中并不常见。

You know, it's just not something that we see in other physical traits.

如果90%的人都是右撇子，那可能是因为这样更好，但为什么不干脆把剩下的10%完全去掉，或者把比例降到零呢？

If 90% of people are right handed, it might be because that's preferable, but then why not just get rid of the 10% completely or push that down to zero?

这到底是怎么回事？

So what's going on here?

今年早些时候发表在《PLOS Biology》上的一项非常有趣的发现是，研究人员研究了灵长类动物以及人类祖先（古人类）和其他灵长类物种的用手习惯。

One very interesting finding from earlier this year reported in Plus Biology was researchers looking at handedness among primates and both human ancestors, hominins, and also other species of primates.

他们试图确定，这种习惯是从什么时候开始形成的？

And they try to pinpoint, okay, where did this set in?

因为其他灵长类动物可能没有固定的偏好，但并没有像人类这样整个物种都偏向使用右手。

Because other primates might have pan preferences, but there's not the species wide bias to the right.

所以这更多是个体偏好，比如，这只灵长类用右手从罐子里取食物。

So it's more of an individual preference like, oh, this primate uses the tube to retrieve the food in the jar with its right hand.

那只用左手。

This one uses its left hand.

这只是个体层面的发展。

That just develops on an individual level.

但只有人类有这种群体层面的偏好。

But it's humans who have this population wide bias.

他们的研究表明，用手习惯大约在七百万年前就形成了，也就是在人类谱系开始的时候，那时我们开始直立行走，这很有道理。

And their study suggested that handedness set in around seven million years ago, so at the start of the hominin line, and that was when we became bipedal, which makes a lot of sense.

一旦我们能站起来，就可以用手去做一些不对称的事情，不只是在地上爬，而是可能这只手做一件事，那只手做另一件事。

Once we can stand up, we can start using our hands for things, for asymmetrical things, not just pushing ourselves along the ground, but rather maybe I can do something with this hand and do something else with this one.

所以偏好就是从那时开始的。

So that's really when this preferences started.

后来大约三百万年前，人类这一支开始出现时，右利手的偏向才确立下来。

And then later around three million years ago when the human line began was when the bias towards the right set in and got established.

这仍然是个谜，

Still a mystery

为什么会这样。

as to why that happened.

为什么那时候我们会偏向右边？

Why back then we would go right?

对。

Yeah.

更难解释的是这种九比一的比例。

The harder thing to explain is this 9010 situation.

而不是刚好一半一半。

Versus just just being fifty fifty.

对。

Yeah.

因为我们身上还有很多其他东西就是固定偏向一边的。

Because there's many other things about us that are just rigidly one thing or the other.

除了惯用手之外，我们并不是完全对称的。

It's not like we're fully symmetric otherwise except for handedness.

不是。

No.

我们是不对称的。

We're asymmetric.

我们的心脏在

Our hearts are on

左边

the

左边。

left.

肝脏在右边。

Our liver is on the right.

你的心脏还是在左边。

Your heart is still on the left.

对吧？

Right?

我的心脏还是在左边。

My heart is still on the left.

对。

Yeah.

我又不是那种器官反位的人。

It's not like I'm a switched person.

所以，是的，我们的身体有很多不对称的地方。

So, yeah, there's a lot about our bodies that's asymmetric.

还有一种情况，就是当你的身体是大多数人的镜像时，这种情况可能非常危险，并且伴随很多其他问题。

And that citizen versus it's called when your body is a mirror image of most people can be a very dangerous condition associated with a lot of other issues.

所以，建立我们身体左右轴的过程是完全独立的。

So the process that establishes our left right axis in our bodies is totally separate.

这个过程在发育过程中发生得更早，而且实际上已经被研究得很清楚了。

It's happening even earlier during development, and that process is actually well understood.

就是细胞表面的纤毛，以某种顺时针方向旋转，产生一股流，把其他分子推向左边，从而确定左右方向。

Its cilia on the surface of the body of cells is, like, swirling around in a certain clockwise way that creates a current that pushes other molecules to the left and establishes left versus right.

这就是那里发生的事情。

And that's what's happening there.

所以这个过程和决定惯用左右手的过程是分开的。

So that process is separate from whatever is going on with handedness.

同样，在我们的大脑中，大多数人处理语言是在左脑，很多左撇子也是这样。

Similarly, in our brains, most people process language on the left sides of our brains, and that's still true also in many left handed people.

但左撇子确实有倾向在大脑两侧处理语言。

But left handed people do have a tendency to process language either in both sides of the brain.

所以，关于我们的手，除了让右侧的运动神经回路更发达之外，它其实也影响了大脑右侧正在发育的其他方面。

So something about our hands is actually as well as causing our motor circuitry on the right to become more developed, it's also affecting other things that are developing on the right side of our brain.

所以，左撇子的大脑里，事情会变得有点混乱和个体化，这可能像我们之前讨论的那样，有一些优势。

So things get a little bit more messy and individualized in a left handed person's brain, which might have advantages as we've discussed.

比如，也许这有助于某些类型的思考。

Like, maybe that helps with certain types of thinking.

但总的来说，这并非完全的翻转。

But, overall, it's not a total switch.

这跟惯用手有一定关联，但大脑仍然试图建立和其他人一样的左右不对称性。

It's somehow correlated with handedness, but the brain's still trying to establish the same asymmetries as in every other person.

我们没法回到

We can't go

三百万年前，但你在研究中遇到的一些比较推测性或有趣的进化理论，能解释为什么我们会保持这个比例呢？

back in time to three million years ago, but what were some of the kind of more speculative or interesting evolutionary theories you encountered that would explain why we would maintain this ratio?

其中一个最著名、目前也最受支持的理论，是所谓的“战斗假说”的改良版。

One that is probably most famous and also probably most supported at this point is a modified version of what's called the fighting hypothesis.

这个理论是九十年代提出的，我记得小时候听说过，当时还更自豪了。

So this came around in the nineties, and I remember hearing about it as a kid and being even more proud of myself.

最初的战斗假说说，左撇子在打斗中有优势，因为出人意料。

So that original fighting hypothesis says that lefties have an advantage in fights because of the element of surprise.

所以左撇子存在的原因，就是因为当左撇子比例低到让人意想不到时，就有了这种优势。

So somehow the reason there's any left handedness at all is because when it's at that low level to where it is surprising to people, then there's this advantage.

但这个理论只能解释为什么左撇子不是零。

But that theory really explains why it's not 0% left handedness.

它解释不了为什么大多数人都是右撇子。

It doesn't explain why most people are right handed.

所以几年前，有些作者提出了修正版的战斗假说，说右撇子有一个基本优势，这也是右撇子占主导的原因，那就是我们的心脏在左边。

So then a few years ago, some authors came along with the modified fighting hypothesis, which says, okay, there is a basic advantage that righties have, which is the reason for the dominance of right handedness, which is the fact that our hearts are on the left.

所以我们的身体左侧，也就是躯干左侧，更脆弱，需要更多保护。

So the left sides of our bodies, our torsos, are more vulnerable, need to be protected more.

所以右撇子打架的时候，会把右侧朝前，至少攻击时右侧朝前。

So right handed people, when they're fighting, stand with their right sides forward, at least attack right side forward.

他们是在保护自己的左侧。

They're protecting their left.

而左撇子必须用左手攻击，这样就会把心脏所在的左侧暴露出来，增加受伤的风险。

And lefties have to attack with their left hand, they're opening up their body to vulnerability with their heart being on the left.

随着人类开始出现严重的暴力冲突，左撇子这个小小的劣势可能最终在基因层面产生了巨大的影响——更多的左撇子被杀，最终导致了右撇子占主导地位。

And so with the start of seriously violent combat with the rise of humans, it could be that that small disadvantage that lefties had really had a huge ultimately genetic effect that more lefties were killed, eventually leading to this right handed dominance.

而今年，提出修正版战斗假说的那几位作者又发表了一篇论文，研究了真实的锐器伤害，分析了受伤模式，结果发现人们确实因为右撇子主导而更多被刺伤左侧，而且左侧的刺伤比右侧的刺伤更容易致命。

And then this year, those same authors of the modified fighting hypothesis came out with a paper that looked at actual sharp force injuries, studies of patterns of injury, and they found that people really are stabbed significantly more on their left sides because of right handedness and that these attacks on the left side are more often fatal than stabs on the right side.

所以这很可能就是主要原因之一。

So that really could be a big part of the reason.

不过，这个假说的一部分是，在右撇子占主导的环境下，左撇子仍然有一点优势，因为那种出其不意的效果。

Part of this hypothesis, though, is that there's still a slight advantage to being a lefty within the context of right handed dominance because of that element of surprise.

而且还有很多其他类型的打斗并不涉及刺心脏。

And there's many other kinds of fighting that don't involve stabbing someone in the heart.

所以在那些情况下，左撇子可能仍然有这个优势。

So in those forms, maybe a lefty still has this advantage.

所以左撇子的比例不会降到零。

So it doesn't get pushed all the way to 0% left handedness.

我觉得这个说法挺有说服力的。

I think that that's a pretty compelling picture.

不过话说回来，这也只是推测。

But again, it's speculative.

我们没法回到过去去验证。

We can't go back in time and figure that out.

不过听起来确实很有道理。

That seems to make a lot of sense though.

心脏保护不了，那直接就被淘汰出基因库了。

Not be able to protect your heart, that'll just knock you out of the gene pool.

对吧？

Right?

所以自然就偏向那边了。

So then you'd bias that way.

不过话说回来，10%应该就是那个最佳比例，你懂的，从数字上看。

But then, yeah, the 10% must be the sweet spot, you know, numerically.

所以科学家说这个比例在不同文化和时代都很稳定。

So scientists say it's very stable across cultures and time.

实际上，人群中左撇子的比例被精确到了10.6%。

So it's actually 10.6% has been pinpointed left handedness in the population.

我在想这个解释够不够充分。

I wonder if that is enough of an explanation.

我有时候会想，是不是对左撇子的偏见，让本来可能更小的不对称性，随着时间被放大了。

Part of me has always wondered whether the bias against left handedness has led to something that could have been a smaller asymmetry kind of getting exaggerated over time.

你知道，在我们这个时代，对左撇子的偏见已经不多了。

You know, in our current era, there's not a lot of prejudice against lefties.

但直到七十年代，小孩用左手写字还会被强制改过来。

But up until the nineteen seventies, kids trying to write with their left hand were made to switch.

我读过一本五十年代的书，讲的是怎么训练孩子用右手，当他们想用左手的时候。

I was reading this book from the fifties about how to train your child to use their right hand when they're trying to use their left hand.

你知道吗，那本书讲的是，左撇子会面临更多的伤害。

You know, it was about how, like, they're gonna be facing more injuries.

所有的机器都是为右撇子设计的，所以左撇子找工作会很难，所以你应该让他们改用右手。

All of this machinery is built for right handed people, so they're gonna face difficulty getting a job if they're a left handed person, so you should switch them.

长期以来，左撇子一直背负着很大的污名。

There was so much stigma against it for so long.

而且就像你说的，我们的语言本身就带有这种偏见。

And as you talked about, our very language is encoded with that stigma.

所以有可能人类文化或社会对右撇子的强烈偏好，导致左撇子在基因库中逐渐减少。

And so it could be that human culture or society actually had such a strong preference for right handedness that left handedness did tend to be diminished in the gene pool.

那么，做这个报道让你作为左撇子的体验有什么改变吗？

So how has working on this story changed your experience of being a lefty?

一个就是，听到很多左撇子的反馈，感觉很有趣。

One thing is it's just been fun to hear from a lot of left handers.

那些读者，那些把报道发给认识的左撇子的人。

The readers of the story, the people who are emailing it to their people they know are left handers.

所以我收到了很多左撇子的来信，他们分享了自己的家族史，比如他们和兄弟姐妹都是左撇子，但父母都是右撇子，或者有人觉得自己的右手更有力，但左手做精细动作更灵活，还有各种微妙的、因人而异的用手习惯。

And so I heard from a lot of lefties about just their own family histories, people who they and their siblings were all left handed even though their parents were both right handed, or people who feel that their right hand is much stronger even though their left hand is better for fine motor tasks, and just all of the subtle individualized versions of handedness that you see.

所以这让我再次意识到，作为左撇子，这件事有多重要。

So it's just been a reminder in a way of how important this is when you are a lefty.

虽然克服这些困难感觉不是什么大事，比如杂货店的笔被拴在一边，你够不到，或者那些不方便又烦人的小事，你会觉得，这没什么大不了的。

So even though it doesn't feel like a big deal to have to overcome struggles, the pen at the grocery store being attached to the stylus on one side and you can't reach over to get it Oh, the hard over, you know, to to those little things that are just inconvenient and annoying make you think, oh, it's not a big deal.

但通过这次经历，以及和其他左撇子聊天的乐趣，你会意识到，好吧。

But then with this and just how fun it's been to talk to other lefties, you realize, okay.

这确实是我经历中很重要的一部分。

It is important aspect of my experience.

对。

Yeah.

而且10%的人，那可是很多人啊。

And 10% of people is that's a lot of people.

对。

Yeah.

而且这也不是什么大事。

And it's not a huge deal.

比如说，我们可以学会用另一只手。

Like, we can learn to use our other hands.

截肢者都能学会用另一只手。

Amputees learn to use their other hand.

所以，再说一次，这可能只是我们需要克服的事情，而前几代人只是毫无怨言地克服了。

So, again, it's maybe just something we have to overcome that previous generations just overcame uncomplainingly.

但这又是谜团的另一部分。

But that's even another part of the mystery.

你知道，如果这不是什么大事，而且很容易克服，那它到底有什么意义呢？

You know, if it's not a big deal and it is easy to overcome, then what's the point of it at all?

好的，谢谢你，Natalie，这次谈话非常有趣。

Well, thank you for this super interesting conversation, Natalie.

也谢谢你。

Thank you too.

所以在每期节目的最后，我们都会请嘉宾给听众一个推荐。

So at the end of every episode, we like to ask our guests for a recommendation for listeners.

你有什么推荐吗？

What do you have?

我做过几次这样的推荐，后来发现，大家真正会采纳的推荐，并不是我推荐什么新奇的东西或者很棒的新书。

I've done this a few times, and I've realized that the recommendations that people always actually take from me are not when I'm recommending some newfangled thing or great new book.

而是当我说，你们应该去读经典的时候。

It's always when I say, you should go read the classics.

你们应该读一本真正的好书，一本经得起时间考验、人人都说很棒的书，因为它确实很棒。

You should read a really good book that stood the test of time that everybody says is brilliant because it is.

所以我要推荐的就是托尔斯泰的《安娜·卡列尼娜》。

And so I'm gonna recommend one of those, which is Anna Karenina by Tolstoy.

这是我最喜欢的书之一。

One of my favorite books.

它非常精彩。

It's amazing.

你会对人性的本质有很多了解。

You're gonna learn a lot about the human condition.

我不确定里面有没有讲左撇子的事，但很多内容都有涉及。

I'm not sure if left handedness is in there, but a lot is in there.

我觉得最好的译本是帕维尔和沃洛沃茨基的，这个译本比较新，语言上让人感觉挺现代、挺当代的。

And the best translation, I think, is this Pavir and Volovodsky, quite recent translation that makes it feel quite modern or contemporary in the language.

所以就是《安娜·卡列尼娜》。

So Anna Karenina.

我

I'm

正准备去度假。

about to leave on vacation.

那本书一直在我脑海里转。

That book was kicking around in my head.

哦，我应该带上。

Oh, I should bring.

所以现在我肯定会去读它。

So now I definitely will do it.

谢谢你，娜塔莉。

Thank you, Natalie.

也谢谢你。

You too.

另外，在本周的《Quanta》上，你还可以读到关于人工智能参与一个数学项目、解决著名数学家保罗·埃尔德什提出的数千个问题的文章，以及中微子可能从地球内部产生的最新证据。

Also on Quanta This Week, you can read about how AI is taking part in a math project to solve thousands of problems posed by the famous mathematician Paul Erdrich and the latest evidence that neutrinos can be produced from within the interior of the Earth.

如果你一直喜欢《Quanta》播客，请花点时间给节目评分并留下评论。

If you've been enjoying the Quanta Podcast, please take a moment to rate the show and leave a review.

我们很期待听到你的反馈。

We'd love to hear from you.

这个播客来自《Quanta》杂志，这是一份由西蒙斯基金会支持的独立编辑出版物。

The Podcast is a podcast from Quanta Magazine, an editorially independent publication supported by the Simons Foundation.

我是汉娜·沃特斯，《Quanta》的高级编辑。

I'm Hannah Waters, a senior editor at Quanta.

西蒙斯基金会的资助决定不会影响本播客或《量子杂志》在选题、嘉宾或其他编辑决策上的独立性。

Funding decisions by the Simons Foundation have no influence on selection of topics, guests, or other editorial decisions on this podcast or in Quanta Magazine.

《量子播客》是与PRX制作公司合作制作的。

The Quanta Podcast is produced in partnership with PRX Productions.

制作团队包括阿里·巴德纳、黛博拉·J.

The production team is Ali Budner, Deborah J.

巴尔萨泽、吉纳维芙·斯庞斯勒和汤米·巴扎里安。

Balthazar, Genevieve Sponsler, and Tommy Bazarian.

PRX制作公司的执行制片人是乔斯林·冈萨雷斯。

The executive producer of PRX Productions is Jocelyn Gonzales.

来自《量子杂志》的西蒙·弗朗斯、萨米尔·帕特尔和我本人提供编辑指导，并得到塞缪尔·贝拉斯科、西蒙娜·巴尔和迈克尔·卡尼翁·戈洛的支持。

From Quanta Magazine, Simon France, Samir Patel, and myself provide editorial guidance with support from Samuel Velasco, Simone Barr, and Michael Canyon Golo.

我们的主题音乐来自APM音乐。

Our theme music is from APM Music.

如果您有任何问题或意见，请发送邮件至quanta@simonsfoundation.org。

If you have any questions or comments for us, please email us at quanta@simonsfoundation.org.

感谢收听。

Thanks for listening.