For years, researchers have tried to understand what drives us to commit acts of violence.

多年來，研究人員一直試圖瞭解驅使我們採取暴力行為的原因。

Is it the environment we were raised in?

是我們的成長環境嗎？

The socio-economic situation we find ourselves in?

我們所處的社會經濟狀況？

Or is it driven by something completely different—something we have no control of—our genes?

還是由完全不同的東西驅動？像是某種我們無法控制的東西－也就是我們的基因？

Or specifically, the so-called 'warrior gene'?

或者更具體地說，所謂的「戰士基因」？

The story of the warrior gene starts in 1978, when a woman walked into a hospital in the Netherlands, and not because she was worried about herself, but because she was worried about her family.

戰士基因的故事開始於 1978 年，一位女子走進荷蘭的一家醫院，但她並不是擔心自己的健康，而是擔心她家人的狀況。

All the men in the family had a history of really terrible violent crimes.

家族中所有的男人過去都有著非常可怕的暴力犯罪史。

There were murders, there were rapes, going back generations and generations.

其中包含各個謀殺案和強姦案，而且可以代代追溯回去。

Researchers started gathering DNA samples from the members of her family, and they discovered that all the men who had this history of very violent crime,

研究人員開始從她的家庭成員中收集DNA樣本，並且發現所有聚極度暴力犯罪歷史的男人們，

they had the same genetic change in a gene called MAOA, or monoamine oxidase A, that completely knocked out the function of the gene. It wasn't working at all.

身上一個叫做 MAOA 的基因，也就是單胺氧化酶中，完全沒有發揮基因的作用。它的功能完全消失了。

We all have two copies of this 'warrior gene'.

而我們每個人的身上都有兩組這種「戰士基因」。

It makes a molecule in your brain that breaks down a chemical called serotonin.

它會在你的大腦中形成一個分子來分解一種叫做血清素的化學物質。

This is a neurotransmitter, it sends signals between the cells in your brain, and affects your behavior.

這是一種神經遞質，會在你的大腦中的細胞之間發送信號，並影響到你的行為。

So if this gene isn't working as well as it could do, it's thought that perhaps it makes you more impulsive, it makes it harder to control urges.

因此如果這個基因沒有妥善的運作，有人認為它會使你變得更為莽撞衝動，讓人難以控制欲望。

So the Dutch study was the first time that this gene, MAOA, had been linked to violent behavior, but then a study in New Zealand took this further.

MAOA 這個基因在荷蘭的研究中第一次被發現時便已與暴力行為相連結，但後來紐西蘭的一項研究則更進一步探討了兩者間的關係。

The Dunedin study followed 1,000 New Zealanders for decades, looking for connections between childhood experiences and violent behavior later in life.

這個在但尼丁展開的研究針對 1000 名新西蘭人進行了幾十年的跟蹤調查，試圖尋找童年經歷與往後的生活中出現暴力行為之間的聯繫。

They found that having a variation that just lowers the level of activity of this gene, not knocks it out completely, but just lowers the activity, was associated with a history of violence.

他們發現，只要基因的變異會降低此基因的活性，就算不是完全使它失去功能，只是降低活性而已，就會與犯罪史相關。

But curiously, mostly only in people who also had a very difficult childhood as well.

但奇怪的是，這個現象大多只被發現在有著艱苦童年的人身上。

And that caught the eye of researchers in Finland working with prisoners in a very high security prison.

而這便引起了正在一個安全級別很高的監獄裡研究囚犯的芬蘭研究人員的注意。

We collected a cohort of around 800 prisoners, and about two-thirds of them had conducted at least one violent crime.

我們收集了一個以約 800 名囚犯所組成的群組，其中約有三分之二的人至少進行過一次暴力犯罪。

But a little bit more than 10% or 15% had committed at least 10 violent crimes, murders, attempted murders, manslaughters.

但比 10% 或 15% 稍微多一點的人曾犯下至少 10 起暴力犯罪，其中包括謀殺、謀殺未遂和屠殺。

I was skeptical, but what we did find was indeed if an individual had two or more violent crimes, then he or she had significantly more of the low activity MAOA.

我本來很懷疑，但我們確實發現了如果一個人有兩次或更多的暴力犯罪行為，那麼他或她有明顯具有更多的低活性 MAOA。

We know that up to six in ten people are walking around with a low activity version of MAOA, but of course, six out of ten people don't commit horrific violent crimes.

我們知道每十個人中有六個人的體內有著低活性版本的 MAOA，但這當然不代表十個人中就有六個人會犯下可怕的暴力罪行。

So obviously we can't say that if you've got this gene variation you are going to be a violent criminal. Genetics doesn't really work like that.

所以顯然我們不能說只要你有這種基因變異，你就會成為一個暴力罪犯。遺傳學不是這樣運作的。

But this idea that there's a gene behind violent behavior, could you use that as a defense in court?

但這種認為「暴力行為的原因是背後有一個基因在推動」的想法，能不能在法庭上作為辯護的籌碼？

You know, "It wasn't me, guv. It was my genes that made me do it."

你知道，「我不是故意的，先生。是我的基因要我這樣做的。」

While it might sound a bit strange, but that is actually what's happening.

雖然這聽起來可能有點奇怪，但這實際上確實正在發生。

It's only really been used in two countries, two in an Italian court and the rest have been in American courts.

只有兩個國家的法庭中曾有使用它作為辯護依據的案例，其中兩個案子在義大利，其餘的都是在美國的法庭上。

It's been used as a way of saying that the person lacked control.

它被用來說明一個人缺乏控制力。

I think it's the sort of evidence that is attempting to be used to dazzle a jury.

我想這就是那種試圖讓陪審團從罪行上分心的證據。

In the US, where you have the death penalty for these kinds of incredibly violent crimes, the stakes are obviously, literally, life and death.

由於美國仍會對極端暴力的罪行執行死刑，因此打官司的風險真的是在生與死之間拔河。

So lawyers will try and introduce any kind of evidence they can to argue against the death penalty for their client.

因此律師們會試圖引入任何他們可以引入的證據，為他們的客戶辯護來避免死刑判決。

To say that there is a gene, like a time bomb that none of us are aware of, I think is wishful thinking.

我認為說我們體內有個沒人能注意到，就宛如定時炸彈一般的基因，其實是種一廂情願的想法。

So humans carry different versions of the MAOA gene, and those that reduce the activity of this gene have been linked to increased risk of aggressive behavior.

人類體內有著不同版本的 MAOA 基因，而降低該基因活性的基因已被認為與攻擊性行為風險的上升有關。

Some studies also suggest a link between an abusive childhood, the MAOA gene not functioning adequately, and an increased risk of developing antisocial personality disorder, which may result in committing violent criminal acts.

一些研究還表明這與艱苦的童年、MAOA 基因沒有充分地發揮作用以及增加患反社會人格障礙的風險有關，而以上狀況都可能會導致犯下暴力犯罪行為。

But whilst it can be tempting to paint a simple picture of how genetics influence our behavior, in reality, it's an incredibly complex issue.

然而，儘管就這樣將基因影響我們行為的方式簡單描繪出來會許顯得輕鬆得多，但這實際上是個非常複雜的問題。

Everything that happens to us interacts with our genes and influences who we are and how we behave.

發生在我們身上的一切都與我們的基因相互作用，並影響到我們的人格和我們的行為方式。

The fact that we can find a connection between genes and violent behavior doesn't mean that we're going to be heading towards some terrible genetic dystopia where little Johnny is locked up because he's got 'bad genes' that might make him do bad things.

就算我們可以找到一個聯繫基因與暴力行為之間的關聯，仍不意味著我們將走向某種可怕的遺傳性烏托邦，讓小約翰尼會因為他有著可能會讓他做壞事的「壞基因」而被關了起來。

That simply isn't how genetics work.

這根本不是遺傳學的工作原理。

We have agency, we have independence, we can make our own free choices about who we are and how we behave.

我們有自主能力，我們有獨立性，我們可以對想要作為怎麼樣的人和我們的行為，憑著自己的自由意志做出選擇。