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So I recently took one of those at-home DNA ancestry tests.
话说，我最近做了一个在家就能做的基因检测。
All I had to do was fill up a vial with a disgusting amount of spit and mail it off for analysis.
我只需要把一个小瓶子装满恶心的唾液，然后寄出去分析就可以了。
We're gonna be here for a very long time.
我们还得弄很久。
I just spit it back up in my nose.
我刚刚把唾液弄到我鼻子里了。
A couple weeks later, this is what I got:
几周后，我收到了检测结果：
It's a neat little pie chart with these specific percentages that were color-matched to different regions on a world map.
一个非常简洁的饼状图，上面有用不同颜色标注的世界各地的具体百分比。
The report told me I was mostly Southwest Asian — no surprises there, considering both my parents are from Iran.
这个报告告诉我，我体内西南亚人的血统所占的比重最大——考虑到我的父母都来自伊朗，这点并不奇怪。
That percentage — 86.7% — I understood that to be the portion of my DNA that’s West Asian.
我的理解就是，我的DNA中有这么大的百分比——86.7%——属于西亚血统。
But it turns out, that’s not exactly what ancestry tests are telling us at all.
但事实证明，这根本就不是基因检测真正要表达的内容。
This is an ad for one DNA ancestry test, 23 and Me.
这是一个基因检测产品广告，广告名字叫“我和23”
An ethnically ambiguous woman travels the world, and a circle animates around her, sort of like the pie chart in my test results,
一位“种族身份模棱两可”的女生在环游世界，画面中，一个圆圈围绕着她，这个圆圈有点像我检测结果中的饼状图，
as if to say, this woman's DNA is 29% East Asian.
就好像在说，这个女人的DNA有29%是东亚血统。
And here's an ad for a different ancestry test.
这是另一则基因检测产品广告。
“52% of my DNA comes from Scotland and Ireland.”
“我有52%的DNA来自苏格兰和爱尔兰。”
And somehow this information compels him to... wear a kilt?
莫名其妙地，这些信息就促使他穿上了……苏格兰小短裙？
Alright, so what are ancestry tests really telling us?
那么，基因检测到底告诉了我们什么呢?
Can you help me understand what my results are telling me?
你能帮我理解一下我的检测结果吗？
Because I’m getting mixed messages from ads and how other people talk about their results.
因为那些个广告和其他人对他们的检测结果的讨论已经把我搞蒙圈了。
This is Wendy Roth.
这位是温迪·罗斯。
"I'm an associate professor of Sociology at the University of British Columbia.
“我是不列颠哥伦比亚大学的社会学副教授。
OK. First of all, these test results are not about your entire DNA.
好的。首先，这些检测结果并不是你整个DNA的检测结果。
They're about a tiny, tiny fraction of your DNA."
它们检测的只是你DNA中很小很小的一部分。”
To understand how genetic ancestry tests work, let’s start with the DNA itself.
为了理解基因检测具体的原理，我们还是要从DNA本身开始说起。
There are about 3 billion base pairs in our genetic code.
我们的遗传密码中有大约30亿个碱基对。
Those are the As, Cs, Ts, and Gs that form the instructions that make us… us.
它们分别是碱基腺嘌呤（简称A）、胞嘧啶（简称C）、胸腺嘧啶（简称T）和鸟嘌呤（简称G），人之为人，就是因为有它们组成遗传指令。
Of these 3 billion base pairs, 99.9% are exactly the same in all humans.
在这30亿个碱基对中，有99.9%的碱基对是所有人都一样的。
But for the remaining .1%, one person might have an adenine where another person has a guanine.
但对于剩下的0.1%，有的人是腺嘌呤，另一个的可能就是鸟嘌呤。
These single-letter differences are called Single-Nucleotide Polymorphisms or SNPs.
这一个字母之差就构成了所谓的“单核苷酸多态性”，简称“SNPs”。
Groups of SNPs can help explain why some people are taller than others
SNP组可以帮助解释为什么有些人比其他人高，
or why some people have green eyes while others have brown eyes.
或者为什么有的人眼睛是绿色，而其他人的眼睛是棕色之类的问题。
But most SNPs have no known effect at all.
但据目前的研究来看，大多数SNP组都是没有任何作用的。
What many DNA tests are looking at are a relatively small number of SNPs,
而许多基因检测为了给你输出检测结果，只关注了数量相当有限的SNP组，
specific positions in this .1% in our DNA, in order to give you your results.
也就是我们的DNA中这0.1%的基因中的某些位置。
When a testing company receives your sample,
检测公司收到你的（唾液）样品后，
they compare your pattern of SNPs to different reference populations in their database.
他们拿你的SNP样式对比数据库中的不同参考人群的SNP样式。
These reference populations contain SNPs known to exist more frequently in different modern populations in the world.
而这些参考人群DNA中含有的是目前世界上不同现代人群中出现频率最高的单核苷酸多态性。
Then the testing company will give you a percentage
然后，检测公司就会给你一个百分比，
that represents how strongly your pattern of SNPs resembles that group.
代表你的SNP模式与特定组的SNP样式相似度有多高。
But this process has a bunch of important limitations and this is where things get complicated.
问题是，检测过程中有很多重要的局限性，会让问题变得更加复杂。
Lots of markers are found in multiple populations around the world.
DNA上的很多标记都是不止一个人群才有的标记。
First, even trying to classify humans into groups in the first place is tricky.
首先，试图对人类进行分类这一尝试一起头就很困难。
Human genetic diversity isn’t organized neatly into groups like countries or continents.
人类的基因多样性并不能像国家或大陆那样进行干脆利落的划分。
Take a look at the distribution of this SNP that affects how a person absorbs folic acid.
不信我们不妨看看这个影响人体吸收叶酸的SNP的分布。
It’s commonly found in Mexico, but also in Chile, or even China, just as often.
这种SNP在墨西哥很常见，但在智利也很常见，甚至在中国也很常见。
So let's say that a particular marker is found in the South Asian population 30 percent of the time.
所以，假设有一种特定的标记有30%的几率出现在南亚人群中。
There's still a possibility that when you inherited this marker you got it not from somebody who was South Asian,
那当你遗传了这个标记时，你仍然有可能不是从南亚人群中的某个人身上遗传过来的，
but from somebody who was in some completely different group that also happened to have that marker.
而是从截然不同但碰巧也有这种标记的人群中的某个人身上遗传来的。
