Once there was a Neanderthal who was cleaning an animal skin.

曾經有一個尼安德特人正在清理一塊動物皮。

They were holding the skin between their teeth while pulling it tight and scraping it with a stone tool.   

他們把皮夾在牙齒之間，同時拉緊它，用石器刮去污垢。

And every now and then, the scraper would slip and accidentally scratch their front teeth.   

不時地，刮削工具會滑動，意外地刮傷他們的門牙。

This individual lived about 130,000 years ago in what's now Croatia.

這個個體生活在約13萬年前的克羅地亞

And the scratches that these random accidents left on their teeth reveal important clues about the hands that made them. 

這些意外留在他們牙齒上的刮傷揭示了製作它們的手的重要線索。

Based on the orientation of these scratches, and those on teeth found from other sites, anthropologists have figured out that most Neanderthals were right-handed, just like most of us Homo sapiens. 

根據這些刮傷的方向和其他地點發現的牙齒上的刮傷，人類學家發現大多數尼安德特人像我們智人一樣是右撇子

70 to 95 percent of us, to be exact, including me.

佔了70%到95%。包括我在內。

But today, no other placental mammal that we know of prefers one side of the body so consistently, not even our closest primate relatives.   

但是今天，我們所知道的其他胎盤哺乳動物中，沒有一種像我們的近親靈長類那樣一致地偏好身體的一側。

And not only that, but no human population has ever been recorded as being mostly left-handed. 

而且沒有任何人類族群被記錄為主要是左撇子。

It turns out that our preference for one hand over another might be tangled up with some of the other unique traits that we inherited from our ancestors,

事實證明，我們對一隻手的偏好可能與我們從祖先那裡繼承的其他獨特特徵纏繞在一起，這些祖先在我們的族群與黑猩猩分開後：

after our lineage split with chimpanzees: namely, walking upright and making stone tools.

即，直立行走和製作石器工具。

In fact, being right-handed may have deep evolutionary roots in our lineage.  

事實上，偏愛右手可能在我們的演化譜系中有著深厚的根源。

And yet, being a leftie does seem to come with some unexpected advantages. 

然而，成為左撇子似乎確實帶來了一些意外的優勢。

Now, we generally think of being right or left-handed to mean preferring to use one hand over the other. 

現在，我們通常認為偏愛左手或右手意味著更喜歡使用一隻手而不是另一隻手。

But it's actually more complicated than that. 

但實際上情況比較複雜。

Handedness seems to be more of a spectrum, with some people being strongly right or left-handed, and others being somewhere between the two. 

偏右或偏左似乎更像是一個光譜，有些人是強烈的右撇子或左撇子，而其他人則介於兩者之間。

And we can also do a lot of different things with our hands, from simply holding an object all the way to precise, delicate manipulation, like threading a needle.   

我們的手還可以進行各種不同的事情，從簡單地拿著物體到精確而細緻的操作，比如穿針引線。

People who generally prefer their right hand for tasks that require fine motor skills could be said to be right-handed, but they still use their left hands a lot in their daily lives. 

通常偏好用右手進行需要精細動作的任務的人可能被視為右撇子，但他們在日常生活中仍然經常使用左手。

Take something like cutting up a carrot - I'd hold the knife in my right hand and do most of the work with it, but I'd still hold the carrot on the cutting board with my left.   

拿切蔬菜這件事，我會用右手拿刀，大部分工作都是由右手完成，但左手仍然會拿著切割板上的胡蘿蔔。

Now, like in all vertebrates, each hand is controlled by a different side of our brain.  

現在，就像所有脊椎動物一樣，每隻手都由我們大腦的不同一側控制。

The left hemisphere controls the right side of our bodies, and vice versa. 

左半球控制身體的右側，反之亦然。

Also, the two hemispheres of our brain aren't perfectly symmetrical, which leads to different cognitive processes taking place in different parts of the brain.   

此外，我們大腦的兩個半球並不完全對稱，這導致不同的認知過程在大腦的不同部分進行。

This separation is known as lateralization, and it's found in all vertebrates and some invertebrates too, and allows us to simultaneously process different types of information. 

這種分離被稱為側化，它在所有脊椎動物和一些無脊椎動物中都存在，使我們能夠同時處理不同類型的信息。

But like many other traits, asymmetry and lateralization are pretty extreme in us humans, especially compared to other primates.   

但就像許多其他特徵一樣，不對稱和側化在我們人類中相當極端，尤其是與其他靈長類相比。

And this may be part of the reason that we eventually came to prefer one hand over another. 

這可能是我們最終偏好一隻手而不是另一隻手的原因之一。

Ninety-nine percent of people have a dominant hand.   

99%的人有一隻優勢手。

And there's lots of evidence that it's been this way for a long time. 

有很多證據表明這種情況已經持續很久了。

Cave paintings all over the world from the Late Pleistocene depict wild animals, hunting events, and notably, a ton of human hands. 

來自更新世晚期的世界各地的岩畫描繪了野生動物、狩獵事件，尤其是大量的人手。

To make these hands, an artist probably placed one hand on the rock and then sprayed pigment over it by blowing into a straw-like tube, leaving an outline of the hand.   

為了製作這些手，藝術家可能會將一隻手放在岩石上，然後向一根稻草狀的管子中吹氣，將顏料噴在上面，留下手的輪廓。

And interestingly, the vast majority of the hands on the walls are left hands. 

有趣的是，牆上絕大多數的手都是左手。

So, experiments that recreated this method have shown that these artists were predominantly right-handed.   

實驗表明，使用這種方法重新創建的藝術家主要是右撇子。

Hand preference in our species is often so strong that you can even see it in the skeleton, especially among athletes like tennis players who use one arm a lot more than the other.

我們物種中的手的偏好通常是如此之強烈，以至於你甚至可以在骨骼中看到它，特別是在像網球選手這樣的運動員中，他們的一臂比另一臂多使用得多。

The bone of their dominant upper arm becomes thicker in certain places compared to the bone of their non-dominant arm, because they're subjecting it to more force, more often. 

他們支配性上肢的骨骼在某些地方變得比非支配性上肢的骨骼更厚，因為他們將其受到更多力量的作用，更經常地這樣做。

In fact, although we're the only species on Earth today that's so strongly handed, there's a lot of evidence that our extinct hominin relatives - that is, the members of our lineage after the split with chimpanzees - were mostly right-handed, too. 

事實上，盡管我們是地球上唯一一種如此強烈偏右的物種，有很多證據表明我們已滅絕的同種親戚 - 即我們與黑猩猩分裂後的族群成員 - 也大多是右撇子。

And weirdly enough, some of the oldest unambiguous evidence comes from teeth.   

奇怪的是，一些最古老的確切證據來自牙齒。

Scientists had already suspected that Neanderthals were mostly right-handed based on their upper arm bones.

科學家已經懷疑尼安德特人的上肢骨頭表明他們大多是右撇子。

Like a right-handed tennis player, Neanderthals had thicker upper arm bones in their right arms than their left arms.    

就像一個右撇子的網球選手一樣，尼安德特人的右臂上肢骨比左臂上肢骨更厚。

But it's rare to find fossils of earlier hominins with bones from both arms preserved in order to compare them.   

但是發現早期同種親戚的骨骼保存有兩只手的骨骼以進行比較是罕見的。

So when scientists found microscopic scratches on Neanderthal teeth that were caused by tools, like those found on that Croatian specimen, they began to wonder about two things.

因此，當科學家在尼安德特人的牙齒上發現了由工具引起的微小刮傷，就像克羅地亞標本上發現的那樣，他們開始思考兩件事。

First, how far back in the fossil record could this evidence for handedness be recognized, 

首先，在化石記錄中這種有關手性的證據可以追溯到多久，

and, second, what other behaviors could handedness be associated with?   

其次，手性還可能與哪些行為有關？

As it turns out, hominins have been using their teeth basically as a third hand for quite a while.

事實上，同種親戚很長一段時間以來一直把牙齒用作第三只手。

So pretend you're pulling a piece of animal hide tight, between your front teeth and your left hand, stretching it out in front of you, and holding a sharp stone tool in your right hand.  

假設你正在用前牙和左手拉緊一塊動物皮，將其伸展到你面前，並用右手持一把尖銳的石器工具。

To clean the hide, you scrape the tool across it from left to right. 

為了清理動物皮，你用工具從左到右刮過去。

If you slip and scratch your teeth, those scratches go from the upper left corner to the lower right corner of your incisors.

如果你滑倒並刮傷牙齒，這些刮痕會從門牙的左上角延伸到右下角。

If you were holding the stone tool in your left hand, they would go the opposite direction - from upper right to lower left. 

如果你用左手拿著石器，它們會朝相反的方向移動－從右上到左下。

Similar scratches like these were found on 500,000-year-old teeth from Spain belonging to a large group of Homo heidelbergensis, the species that might be our last common ancestor with Neanderthals. 

在來自西班牙的 50 萬年前的牙齒上也發現了類似的划痕，這些牙齒屬於一大群海德堡人，該物種可能是我們與尼安德特人最後的共同祖先。

And those scratches have even been detected on the teeth of a Homo habilis from Tanzania that was 1.8 million years old! 

甚至在180萬年前坦尚尼亞能人的牙齒上也發現了這些刮痕！

While, one right-handed Homo habilis doesn't mean the whole species was right-handed, it's clear that handedness itself is pretty old. 

雖然一個能人是右撇子並不意味著整個物種都是右撇子，但很明顯，左撇子本身就相當古老。

And because no other primate species has extreme hand dominance, this trait must have emerged after our split from chimpanzees. 

而且由於沒有其他靈長類動物具有極端的手部優勢，因此這種特徵一定是在我們與黑猩猩分離後出現的。

But, why did more than one hominin species start preferring one hand in the first place?

但是，為什麼不只一種人類物種一開始就開始偏愛一隻手呢？

And, what's so special about the right hand anyway?

而且，右手有什麼特別之處呢？

Many studies have turned to genetics to try to find the elusive "handedness" gene.    

許多研究轉向遺傳學，試圖找出難以捉摸的「慣用手」基因。

Observations of families and genetic analyses have shown that handedness does appear to be somewhat heritable, and that men are left-handed more often than women. 

對家庭的觀察和遺傳分析表明，慣用手確實具有一定的遺傳性，而且男性左撇子的比例高於女性。

But, many searches through our genome haven't found the gene that's responsible for left or right handedness.

但是，對我們基因組的多次搜尋並沒有找到導致左利手或右手利手的基因。

Instead, it seems  like several genes may have some minor effects, and that other factors might also be at play. 

相反，似乎有幾個基因可能會產生一些微小的影響，而且其他因素也可能在起作用。

So, other scientists have focused on the importance of brain lateralization and tool use.   

因此，其他科學家將注意力集中在大腦偏側化和工具使用的重要性。

Brain scans of people performing a variety of tasks have shown that a specific region of our left hemisphere, called BA44, plays an important role in manipulating objects, including making and using tools.   

對執行各種任務的人的腦部掃描表明，我們左半球的一個特定區域（稱為 BA44）在操縱物體（包括製作和使用工具）方面發揮著重要作用。

Since the left hemisphere controls the right hand, it's possible that the development of tools millions of years ago led to this hand eventually being favored across hominin species.   

由於左半球控制右手，因此數百萬年前工具的發展可能導致這隻手最終受到所有古人類物種的青睞。

And having a species-wide hand preference at all may be linked to an even older trait: bipedalism. 

擁有整個物種的手的偏好可能與一個更古老的特徵有關：直立行走。

Some other bipedal mammals, like kangaroos, seem to have a hand preference, which suggests that not moving on all fours may have something to do with it.   

一些其他直立行走的哺乳動物，如袋鼠，似乎有手的偏好，這表明不使用四肢移動可能與此有關。

What's interesting is that these kangaroos are mostly left-handed, and they don't use tools like we do.   

有趣的是，這些袋鼠大多是左撇子，而且他們不像我們一樣使用工具。

So, if us being right-handed is somehow related to tool use and our left hemisphere, then why are there any lefties today at all?   

所以，如果我們的右撇子與工具使用和我們的左半腦有某種關聯，那為什麼今天還有左撇子呢？

 While we still don't know for sure, it's possible that at some point after the development of stone tools, everyone became right-handed.   

雖然我們還不能確定，但有可能在石器發展後的某個時刻，每個人都變成了右利手。

In this scenario, left-handedness may have emerged later, as a result of one or several genetic mutations.   

在這種情況下，左撇子可能是在石器發展之後的某個時刻出現的，可能是由於一種或多種基因突變。

And since lefties make up a pretty consistently small portion of the population in our largely right-handed world, there must be some kind of evolutionary advantage. 

由於在我們主要是右撇子的世界中，左撇子在人口中佔據了相當一致的小部分，必定存在某種進化優勢。

And this, too, might all go back to lateralization.   

這也可能與側化有關。

Experiments and brain-scan studies have shown that lefties tend to have less lateralized brains than righties.   

實驗和腦掃描研究顯示，左撇子的大腦側化比右撇子少。

This means that they process information more evenly across their brains, and this may be associated with better coordination, memory, and verbal skills. 

這意味著他們在整個大腦中更均勻地處理信息，這可能與更好的協調、記憶和語言技能有關。

Plus, according to several studies, it also gives them an unexpected edge in physical combat.   

此外，根據幾項研究，這也使他們在身體戰鬥中獲得了意外的優勢。

Imagine you're in a boxing match. If you're right-handed, and you've only encountered right-handed opponents, you'll probably be expecting hits to come from your opponent's right hand. 

想像一下你在拳擊比賽中。如果你是右撇子，並且只遇到過右撇子的對手，你可能會預期對手的打擊來自右手。

But if your opponent is left-handed, they'll have the advantage of surprise, because they'd be striking from an unexpected angle. 

但是如果你的對手是左撇子，他們將擁有意外的優勢，因為他們會從意想不到的角度進行打擊。

This left-handed advantage is seen in a range of interactive sports today and is absent in non-interactive sports, like darts.

這種左撇子的優勢在當今的一系列互動性體育項目中都可以看到，但在非互動性體育項目中卻不存在，比如飛鏢。

And it seems to be stronger in men than in women.   

而且在男性中似乎更為明顯。

One study from 2019 even found that left-handed boxers and mixed martial artists win matches significantly more often than their right-handed opponents. 

一項來自2019年的研究甚至發現，左撇子的拳擊手和混合武術運動員比右撇子的對手贏得比賽的機會顯著更多。

This benefit could've directly led to increased survival among left-handed people.   

這種好處可能直接導致了左撇子的生存增加。

And it might also explain why the frequency of left-handers is so low: if too many people are left-handed, the advantage disappears.    

這也可能解釋為什麼左撇子的頻率如此之低：如果太多人是左撇子，這種優勢就會消失。

Like tool use, bipedalism, and being relatively hairless and sweaty, being right-handed seems to have a deep evolutionary history in our lineage.   

就像使用工具、直立行走以及相對禿頭和多汗一樣，偏右似乎在我們的譜系中有著深厚的演化歷史。

Thanks to our highly lateralized brains, many of the mental processes that we use to make tools are concentrated in one area, which in most of us, happens to be in the left hemisphere. 

由於我們高度側化的大腦，我們用來製作工具的許多心理過程集中在一個區域，這在我們大多數人中恰好在左半腦。

And since this hemisphere also controls the right side of our bodies, we tend to favor this hand more often.

由於這一半腦還控制著我們身體的右側，我們更傾向於更常使用這只手。

While having hand dominance is found in a few other bipedal mammals, no other primate shows the degree of favoritism for one hand that we do.   

儘管手的優勢在其他一些直立行走的哺乳動物中也存在，但沒有其他靈長類動物像我們一樣對一只手表現出如此程度的偏愛。

And even though the exact origin of right hand preference isn't yet clear, lefties might have enough important evolutionary advantages for them to still be around. 

即使右手的偏好的確切起源尚不清楚，左撇子可能因其擁有足夠重要的進化優勢而仍然存在。

It just goes to show how variable we are as a species, and that there's no right…way to be human.

這只是表明了我們作為一個物種有多變，並且並不存在一種正確的……成為人類的方式。

Thanks to Great Courses Plus for Supporting PBS.

感謝Great Courses Plus對PBS的支持。

The Great Courses Plus is a subscription on-demand video learning service with lectures and courses from professors from top universities and institutions. 

Great Courses Plus是一個訂閱式點播影片學習服務，提供來自頂尖大學和機構教授的講座和課程。

Through your subscription, you get access to a library of lectures about anything that interests you...science, math, history, literature, or even how to cook or become a better photographer. 

通過您的訂閱，您可以訪問有關您感興趣的任何事物的講座……科學，數學，歷史，文學，甚至是烹飪或成為更好攝影師的講座。

For example, you should check out The Scientific Wonder of Birds. In this course, 

例如，您應該查看《鳥類的科學奇跡》。在這門課中，

Dr. Bruce E. Fleury covers fascinating topics like the origin of flight, how birds navigate over long distances, and of course, the connections between birds and their extinct dinosaur ancestors.

布魯斯·E·弗勒博士涵蓋了一些迷人的主題，如飛行的起源，鳥類如何長途航行，當然還有鳥類與其滅絕的恐龍祖先之間的聯繫。

To learn more, click on the link in the description below to start your trial today.

要了解更多信息，請點擊下方描述中的連結，開始您的試用。

And we've gotta hand it to this month's Eontologists: Sean Dennis, Jake Hart, Annie & Eric Higgins, John Davison Ng, and Patrick Seifert! 

我們必須感謝本月的“Eontologists”：肖恩·丹尼斯，傑克·哈特，安妮＆埃里克·希金斯，約翰·戴維森·吳和帕特里克·賽弗特！

By becoming an Eonite at patreon.com/eons, you can get fun perks like submitting a joke for us to read, which I'm gonna do now... 

通過在patreon.com/eons成為Eonite，您可以獲得有趣的福利，比如提交一個我們可以閱讀的笑話，我現在就要做...

This one is from Betsy.  

這個笑話來自貝齊。

Why couldn't the Tyrannosaurus get a driver's license? Because T. rex.

為什麼霸王龍不能得到駕駛執照？因為T. rex。

The w is silent and invisible, I guess.

w是無聲且看不見的，我猜。

And as always thanks for joining me in the Konstantin Haase studio.

一如既往地感謝您加入康斯坦丁·哈斯工作室。

Subscribe at youtube.com/eons for more creature features.

在 youtube.com/eons 上訂閱以了解更多生物功能。