Why are some people left-handed? - Daniel M. Abrams

为什么有人是左撇子? - Daniel M. Abrams

翻译人员: Yixuan Zhu 校对人员: Cissy Yun

If you know an older left-handed person,

如果你认识一个比你大的左撇子，

chances are they had to learn to write or eat with their right hand.

他们都有可能曾经被迫学习过用右手写字和吃饭

And in many parts of the world,

在世界上很多地方，

it's still common practice to force children to use their "proper" hand.

依旧有惯例强迫孩子使用“合适”的手

Even the word for right also means correct or good,

就连“右”字，在英语里也代表着正确和好

not just in English, but many other languages, too.

不仅在英语中，其他很多语言也是

But if being left-handed is so wrong,

但是如果左撇子是不对的，

then why does it happen in the first place?

那为什么会有左撇子出现呢？

Today, about 1/10 of the world's population are left-handed.

现今，大约1/10的世界人口是左撇子

Archeological evidence shows that it's been that way

考古证据显示，

for as long as 500,000 years,

这种比例已经存在有50万年了

with about 10% of human remains

约有10%的人显现出

showing the associated differences in arm length and bone density,

差异区别在手臂长度和骨密度上

and some ancient tools and artifacts showing evidence of left-hand use.

古代一些工具和手工艺品也证明有左撇子的存在

And despite what many may think, handedness is not a choice.

尽管很多人认为用手习惯不是一种选择

It can be predicted even before birth based on the fetus' position in the womb.

但在出生前根据胎儿在子宫里的位置就可以预测

So, if handedness is inborn, does that mean it's genetic?

因此，如果习惯是天生 是否就意味着这是基因定的吗？

Well, yes and no.

是 又 不是

Identical twins, who have the same genes, can have different dominant hands.

同卵双胞胎拥有相同的基因也会产生不同的主导手

In fact, this happens as often as it does with any other sibling pair.

事实上，这与其他同胞对的发生概率一样

But the chances of being right or left-handed

你是左撇子还是右撇子

are determined by the handedness of your parents

取决于父母的用手习惯

in surprisingly consistent ratios.

这有惊人的统一数据

If your father was left-handed but your mother was right-handed,

如果爸爸是左撇子，而妈妈是右撇子

you have a 17% chance of being born left-handed,

你有17%的机会是左撇子

while two righties will have a left-handed child only 10% of the time.

而两位都是右撇子，孩子是左撇子的几率只有10%

Handedness seems to be determined by a roll of the dice,

看起来用手习惯像掷骰子一样

but the odds are set by your genes.

但几率是由基因决定的

All of this implies there's a reason

这一切的原由是

that evolution has produced this small proportion of lefties,

进化产生了这小部分的左撇子

and maintained it over the course of millennia.

并保持了上千年

And while there have been several theories

有几种理论

attempting to explain why handedness exists in the first place,

试图去解释为什么一开始有用手习惯存在

or why most people are right-handed,

或者为什么大多数人习惯用右手

a recent mathematical model

最近一个数学模型提出

suggests that the actual ratio reflects a balance

现实比例反应了人类进化中

between competitive and cooperative pressures on human evolution.

竞争和合作压力造成的人数平衡

The benefits of being left-handed

左撇子的好处

are clearest in activities involving an opponent,

很明显是在活动中处对立面

like combat or competitive sports.

像拳击或竞技运动

For example, about 50% of top hitters in baseball have been left-handed.

比如，有50%顶尖棒球击球手都是左撇子

Why?

为什么？

Think of it as a surprise advantage.

那会是很特殊的优势

Because lefties are a minority to begin with,

左撇子很小众

both right-handed and left-handed competitors

左撇子和右撇子的选手都会

will spend most of their time encountering

花大量的时间

and practicing against righties.

练习对抗右撇子

So when the two face each other,

所以当他们面对面对抗时

the left-hander will be better prepared against this right-handed opponent,

左撇子会更熟练地对抗右撇子对手

while the righty will be thrown off.

然而右撇子的就无力对抗了

This fighting hypothesis,

这斗争的假设

where an imbalance in the population

因人数上的不平均

results in an advantage for left-handed fighters or athletes,

造成左撇子的战士或者运动员有优势

is an example of negative frequency-dependent selection.

是一个很好的负频率相关选择的例子

But according to the principles of evolution,

但根据进化法则

groups that have a relative advantage

有相关优势的组群

tend to grow until that advantage disappears.

会发展至优势消失

If people were only fighting and competing throughout human evolution,

如果在人类进化中只有战斗和竞争

natural selection would lead to more lefties being the ones that made it

自然选择会导致左撇子的数量从很少

until there were so many of them,

变为很多

that it was no longer a rare asset.

直到他们不再是稀有资源

So in a purely competitive world,

因此在一个完全竞争环境

50% of the population would be left-handed.

会有50%的人口是左撇子

But human evolution has been shaped by cooperation, as well as competition.

但人类进化史上有合作和竞争

And cooperative pressure

由于合作的压力

pushes handedness distribution in the opposite direction.

造成用手习惯往相反的方向

In golf, where performance doesn't depend on the opponent,

当在高尔夫比赛中，选手的表现不用依赖对手

only 4% of top players are left-handed,

所以只有4%的选手是左撇子

an example of the wider phenomenon of tool sharing.

这是个更广泛现象的工具共享

Just as young potential golfers

像年轻有潜力的高尔夫手们

can more easily find a set of right-handed clubs,

更容易找到右手为主的俱乐部

many of the important instruments that have shaped society

很多重要的装备都是

were designed for the right-handed majority.

为大众的右手选手设计的

Because lefties are worse at using these tools,

因为左撇子都用不惯这些装备

and suffer from higher accident rates,

而且高失误率

they would be less successful in a purely cooperative world,

会使他们在纯合作环境里吃亏

eventually disappearing from the population.

最终造成人数上锐减

So by correctly predicting the distribution

为了能正确预测左撇子

of left-handed people in the general population,

在人群中的分布

as well as matching data from various sports,

以及与各项运动中的数据配对

the model indicates

模型指出

that the persistence of lefties as a small but stable minority

左撇子群体小而且数量稳定

reflects an equilibrium

反应了人类合作和竞争的

that comes from competitive and cooperative effects

平衡影响

playing out simultaneously over time.

他们同时进行着

And the most intriguing thing

最有趣的是

is what the numbers can tell us about various populations.

数据可以告诉我们很多关于人群数量变化中包含的信息

From the skewed distribution of pawedness in cooperative animals,

从有爪动物合作的倾斜分布

to the slightly larger percentage of lefties

到合作狩猎社会里

in competitive hunter-gatherer societies,

比重稍大的左撇子

we may even find that the answers to some puzzles of early human evolution

我们会发现有关早期人类进化的某些难题的答案

are already in our hands.

就在我们手中