为什么人有左撇子和右撇子?
Why Are People Left- (or Right-) Handed?
780字
2019-12-14 12:47
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火星译客

Being a "righty" has historically carried distinct advantages over being a "lefty."

自古以来,右撇子就比左撇子有很明显的优势。

The first time you picked up a crayon as a small child, you probably felt more comfortable and more natural drawing with one of your hands than the other one. 

当你童年时第一次拿起一支蜡笔,你可能就会感觉用其中一只手画画比用另外一只手更加舒服自然。

Excluding the small number of truly ambidextrous people — those who can use their right and left hands with equal ease — humans generally have a dominant hand (and side of their body) that they favor for everyday tasks. 

除了少数双手同样灵活的人以外,人们一般都有优势手(身体也有有优势的一侧),他们更倾向于使用优势手完成每天的工作。

But why is that?

但是这是为什么呢?

Most people — about 85 to 90% — are right-handed, and there's no population on Earth where left-handers are in the majority.

大多数-大概85%-90%的人都是右撇子,世界上没有任何一个种族是左撇子占大多数的。

That uneven split has had some historic downsides for lefties. They've had to use scissors, desks, knives and notebooks that were designed with righties in mind. Many lefties were forced, against their natural inclination, to write with their right hands (including some famous examples like King George VI of England). They've been discriminated against and eyed with suspicion, as evidenced in the language used to describe lefties. "Right" in English obviously also means "correct." The etymology of the word "sinister" can be traced back to the Latin word for "left."

对于左撇子来说,这种不平均的分化为他们带来了一些显著的不便。他们不得不使用为右撇子们设计的剪刀,桌子,刀具还有笔记本。许多左撇子被迫违背天性,改为用右手写字(包括一些著名的例子,例如英国国王乔治六世)。用于描绘左撇子的语言也明显带有歧视和质疑的意味。英语中“右(right)”明显也有“正确”的意思。而拉丁语中的“左”这个词在现今英语却是“阴险”的意思。

While the stigma against left-handedness has faded in most places, scientists are still confounded by the righty-lefty divide. Researchers are still trying to understand what makes people prefer one hand over the other and why righties dominate. 

尽管在大多数地方对于左撇子的偏见已经逐渐消退,但是科学家依然对于这件事情感到困惑。研究人员一直在尝试了解为什么人们会更习惯用一只手,以及为什么惯用右手的人居多。

On an individual level, handedness might be determined at the earliest stages of development. Scientists reported in 2005 in the journal Neuropsychologia that fetuses will show a hand preference in the womb (by sucking the thumb of one hand), a proclivity that continues after they're born. 

从个人层面上来说,惯用右手还是左手可能取决于生命的最初阶段。科学家在2005年神经心理学杂志中提到,胎儿在子宫中就已经显现出惯用哪只手(吮吸左手还是右手的拇指),这种倾向在他们出生后也会一直延续。

While there's no righty or lefty gene, DNA does seem to play a role in handedness. In a recent study published in Brain: A Journal of Neurology, researchers at the University of Oxford looked at the DNA of about 400,000 people in the U.K. and found that four regions of the genome are generally associated with left-handedness. Three out of these four regions were involved in brain development and structure. Some researchers hope that studying the biological differences between lefties and righties could shed light on how the brain develops specializations in its right and left hemispheres. 

尽管没有右手或是左手基因,在用左手还是右手的习惯上DNA似乎还是起了一定的作用。近期发表于大脑:神经学杂志的研究中,牛津大学的研究人员查看了英国40万人的DNA,发现在基因组中有四个区域通常与惯用左手有关。其中三个区域和大脑发育以及构造相关。一些研究人员希望通过研究左撇子和右撇子人们的生物学差异来了解大脑是如何在左右脑中发育各自的功能的。

Trying to answer the question of handedness from an evolutionary perspective is also complicated. Researchers can detect handedness in the archaeological record by looking for certain anatomical traits in prehistoric skeletons, such as asymmetry in the size and density of arm bones, and by examining prehistoric tools. 

从进化学角度来回答惯用左右手的问题同样十分复杂。研究人员可以通过寻找史前骨架上的一些解剖学特征,例如臂骨尺寸和密度的不对称,或者研究史前的工具来断定考古记录中的人类惯用左手还是右手。

"If you know how the tool was held and how it was used, then you can look at the wear traces" to determine if a lefty or righty used the tool, said Natalie Uomini, a senior scientist at the Max Planck Institute for the Science of Human History in Germany. Scientists can even look at the direction of diagonal scratches on fossilized teeth to see which hand people were using to tear off meat or animal hides in their mouths.

德国马克斯普朗克人类历史科学研究所资深科学家Natalie Uomini说道:“如果你知道人类是怎样握住或者使用工具的,你可以通过磨损痕迹来判断使用工具的人是左撇子还是右撇子”。科学家们甚至可以通过牙齿化石上的斜纹划痕来判定人们在嘴中撕肉或动物皮时用的是哪只手。

Righties have dominated for as far back in the archaeological record as researchers can see, about 500,000 years, Uomini said. Neanderthals, our now-extinct human cousins, were also strongly right-handed. 

Uomini提到,研究人员根据考古记录发现早在50万年前右撇子就一直占据多数。现今灭绝的穴居人也是同样以右撇子居多。

That makes humans pretty strange among animals. Several nonhuman species, such as the other great apes, are individually handed, but the split between righties and lefties is typically closer to 50-50.

这一点使得人类在动物中相当奇怪。一些其他的非人类种族,比如大猩猩,它们同样是使用两只爪子,但是左撇子和右撇子的比例基本上是一半一半。

What caused our extreme bias toward right-handedness to evolve and persist? From an evolutionary perspective, if right-handedness evolved because it had some kind of advantage, then you might expect left-handers to disappear completely, Uomini told Live Science. She added that there are some disadvantages to being left-handed, such as higher frequencies of work accidents. Researchers also linked left-handedness to learning disabilities, in a study published in 2013 in Brain: A Journal of Neurology

是什么造成了人类进化成惯用右手?Uomini提到如果惯用右手进化至今是因为它有一些优势,那么惯用左手的人可能已经完全灭绝了。她还补充道,左撇子确实有很多缺点,比如左撇子更容易出工伤事故。在2013年发表于大脑:神经学杂志中的文章中,研究人员还提出左撇子更容易有学习障碍。

But there's a leading theory to explain why left-handers have maintained a constant minority: the fighting hypothesis. 

然而有一个主要理论来解释为什么左撇子一直占少数额:那就是战斗假设。

"The idea is that in hand-to-hand combat, or in combat with weapons, there is an evolutionary advantage to being a minority left-hander," Uomini said. "If you're left-handed, you have a surprise advantage because most people are used to fighting against right-handers." That lefty advantage has been shown in one-on-one sports like fencing, scientists reported in 2010 in the journal Laterality

Uomini说道:“战斗假设提出在肉搏战或者使用武器的战争中,占据少数的左撇子有明显的进化优势。如果你是左撇子,那么你在战争中就占据了奇妙的优势,因为大多数人都更习惯和右撇子打仗。”科学家于2010年的Laterality杂志中提到,左撇子在面对面的运动中有明显优势,例如击剑。

If that hypothesis is correct, it would mean that even though the downsides to left-handedness were significant enough to keep lefties in the minority, lefties' advantage in combat at least gave them a fighting chance against eventual extinction.

如果这项假设是正确的,这就意味着即使左撇子由于自身存在的缺点一直占少数,但是他们在战斗中的优势起码可以让他们不至于完全灭绝。

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