They all married their first cousins.

他們都嫁給了自己的嫡親表親。

You'd think Darwin of all people would know better.

你以為達爾文會更清楚這一點。

After all, mating with a close relative passes on bad genes that leads to deadly genetic mutations.

畢竟，與近親交配會傳遞不良基因，導致致命的基因突變。

Right?

對不對？

Today, marrying your first cousin is illegal in 24 US states.

如今，在美國 24 個州，與嫡親表兄妹結婚是非法的。

But for most of Western history, people had to marry whoever lived nearby, which oftentimes meant marrying within the extended family.

但在西方歷史的大部分時間裡，人們不得不與住在附近的人結婚，這往往意味著在大家族內結婚。

In fact, between 1650 -1850, the average married couple was fourth cousins.

事實上，在 1650 年至 1850 年間，平均每對已婚夫婦都是第四代表親。

So they had the same great, great, great, great grandparents.

他們有相同的曾曾曾曾祖父母。

Genetically speaking, that means they shared 0.2% of their DNA.

從遺傳學上講，這意味著他們共享 0.2% 的 DNA。

Not much when you compare it to 3rd, 2nd and especially first cousins.

與三表親、二表親，尤其是一表親相比，就不算什麼了。

And the more DNA you share, the greater chance your offspring will have a genetic disease like cystic fibrosis or sickle-cell anemia.

你們共享的 DNA 越多，後代患囊性纖維化或鐮狀細胞性貧血等遺傳病的機率就越大。

But here's the thing, you don't have to be sick in order to give your child a genetic disease.

但問題是，不一定非要生病才能讓孩子患上遺傳病。

Take cystic fibrosis. It's caused by a defect in the CFTR gene, but you need two copies of the defective gene to actually get the disease.

以囊性纖維化為例，它是由 CFTR 基因缺陷引起的，但你需要兩個缺陷基因才能真正患上這種疾病。

So if you only have one defective copy, you are unaffected. Instead, you are what's called a carrier.

所以如果你只有一個缺陷基因，你就不會受到影響，你就是所謂的帶原者。

Now, if one carrier meets with a non-carrier, there's no risk of the kids getting sick.

現在，如果一個帶原者與一個非帶原者相遇，孩子們就不會有生病的風險。

But when both parents carry a defective copy of CFTR, then the kids have a 25% chance of inheriting two copies of the gene and having the disease.

但是，如果父母雙方都攜帶有缺陷的 CFTR 基因，那麼孩子就有 25% 的機率遺傳到兩個缺陷基因並患上這種疾病。

So to see how dangerous it is to marry your first cousin, we need to calculate the chances that two first cousins both carry a copy of the same genetic disease.

要想知道與嫡親表兄妹結婚有多危險，我們需要計算兩個嫡親表兄妹都攜帶相同遺傳病的機率。

Since they share a set of grandparents, we'll start there.

既然他們有共同的祖父母，我們就從這裡開始。

Now, it becomes a game of what ifs: what if both grandparents are carriers versus just one?

現在，這變成了一個「如果」問答：如果祖父母都是帶原者而不是只有一個呢？

What if one of their Children is a carrier versus none at all?

如果他們的一個孩子是帶原者，而另一個孩子不是呢？

And what if those Children marry other carriers or not?

如果這些孩子與其他帶原者結婚或不結婚呢？

It can get very complicated very quickly.

這件是可能很快就會變得非常複雜。

But scientists have crunched the numbers and it turns out the risk that the cousins have a kid who inherits a genetic disease is 4 to 7%.

但科學家們對數據進行了分析，發現這對錶兄弟姐妹的孩子遺傳遺傳疾病的風險為 4% 到 7%。

For the general population, it's 3% to 4%.

對於一般人群來說，這個比例是3%到4%。

So, not a big deal. Right?

所以，沒什麼大不了的。對吧？

Here's the catch, that's the odds for one genetic disease.

問題是，這是一種遺傳病的機率。

But there are thousands that could be hiding in your family tree.

但你的家譜中可能隱藏著數千個。

Plus, if your kids also marry their first cousins and their kids marry their first cousins, it's a recipe for disaster,

此外，如果你的孩子也和他們的表兄妹結婚，而他們的孩子又和他們的表兄妹結婚，那就會釀成大禍，

because instead of introducing new, potentially helpful genes into the family gene pool, you're recycling the old and possibly dangerous ones.

因為你不是將新的、可能有用的基因引入家族基因庫，而是回收舊的、可能危險的基因。

Take Emperor Ferdinand the first of Austria, his parents were first cousins twice over.

就拿奧地利皇帝斐迪南一世來說，他的父母是兩代嫡親。

And when he was born, he wasn't especially healthy.

他出生時，身體並不特別健康。

So as far as marrying your cousin is concerned, you shouldn't make it a family tradition.

就與表親結婚而言，你不應該將其作為家族傳統。

What interesting things have you found out in your family tree?

你在家譜中發現了哪些有趣的事情嗎？

Let us know in the comments.

請在留言區中告訴我們。