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This is Scientific American 60-Second Science. I'm Karen Hopkin.
这是科学美国人60秒科学。我是凯伦霍普金。
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Why did the chicken cross the road?
为什么鸡过马路？
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Well, that's a philosophical pickle.
嗯，这是一个哲学的泡菜。
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But if you want to know why chickens don't get cross at people-why they're content being kept in their coops-science can help.
但是如果你想知道为什么鸡不会与人交叉 - 为什么他们的内容被保留在他们的鸡舍里 - 科学可以帮助你。
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"Domestic species are interesting because their genetic makeup has changed dramatically as part of the process of going from wild to domestic."
“国内物种很有意思，因为它们的基因组成已经发生了巨大的变化，这是从野生到家庭过程的一部分。”
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Liisa Loog, an evolutionary geneticist and anthropologist at the Universities of Oxford and Cambridge.
Liisa Loog，牛津大学和剑桥大学的进化遗传学家和人类学家。
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"And indeed when people have compared modern domestic animals with their wild relatives they've identified genes that do show signs of strong recent selection.
“事实上，当人们将现代家畜与他们的野生亲属进行比较时，他们已经发现了确实显示出最近选择强烈迹象的基因。
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One such gene is thyroid stimulating hormone receptor, otherwise known as TSHR...
一个这样的基因是促甲状腺激素受体，也称为TSHR ......
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in chickens, a variant of this gene that is widespread in modern populations has been shown to directly cause chickens to be less fearful of humans and also result in reduced aggression towards conspecifics."
在鸡中，这种基因的变种在现代人群中广泛存在，已被证明可以直接导致鸡对人类的恐惧程度降低，并导致对同种种群的攻击性降低。
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But when exactly did the selection for these traits-and therefore this variant-take place?
但是，当确切地选择这些特征时 - 并因此这个变种 - 发生了吗？”
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"It's been suggested because of the potential usefulness of these traits in domestic setting that selection on this gene must have happened when chickens were first domesticated around 6,000 years ago in East Asia.
“有人建议，因为这些特性在国内环境中的潜在用途是，当这些基因必须在大约6000年前在东亚首次被驯化时，必须选择这种基因。
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But in an evolutionary timescale this is just a blink of an eye and we just don't know and don't have the resolution to tell when exactly between 6,000 years ago and now this selection happened, using data from only modern chicken populations...
但是在进化的时间尺度上，这只是眨眼之间，我们只是不知道并且没有决定在6000年前和现在这个选择发生时，只使用来自现代鸡群的数据。
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but with DNA from archaeological material we can follow what happened with a gene through time and in theory spot when changes in a population occur."
但是，根据考古材料中的DNA，我们可以跟踪基因随时间发生的情况，并在理论上发现人口发生变化时的情况。”
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Loog and her colleagues examined TSHR gene sequences in the ancient remains of about 60 chickens found in Europe" and estimated that selection at this TSHR locus happened only around 1,000 years ago, at medieval times.
Loog和她的同事检查了在欧洲发现的约60只鸡的古代遗骸中的TSHR基因序列“并且估计在这个TSHR基因座的选择仅发生在大约1000年前的中世纪时期。
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That is, 5,000 years after the initial domestication of chicken.
也就是说，最初驯化鸡肉后5000年。
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"Interestingly this time period coincides with a...substantial increase in chicken consumption known from the archaeological record.
“有趣的是，这段时间与考古记录中已知的鸡肉消费大幅增加相吻合。
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Historians suggest that a key driver behind these changes was the rising popularity and spread of Christian traditions, which discouraged and also on occasions even banned eating meat from four-legged animals."
历史学家认为，这些变化背后的一个关键驱动因素是基督教传统的日益普及和传播，这种传统不鼓励，甚至有时甚至禁止吃四足动物的肉。”
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But fowl were fair game.
但是鸡是公平的游戏。
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"What is really exciting about this new study is that for the first time we can directly link genetic changes in domestic animal with cultural shifts in human food preference.
“这项新研究真正令人兴奋的是，我们第一次可以直接将家畜的遗传变化与人类食物偏好的文化转变联系起来。”
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The findings appear in the journal Molecular Biology and Evolution.
该研究结果发表在“分子生物学与进化”杂志上。
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This kind of plucky study is not just for the birds.
这种勇敢的研究不仅适用于鸟类。
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Loog says the team is collecting canine archaeological samples, so they can look at how man's best friend got divvied up into so many different breeds.
Loog说团队正在收集犬类考古样本，因此他们可以看看人类最好的朋友如何被分配到许多不同的品种中。
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Their research will no doubt be dogged.
他们的研究无疑会受到困扰。
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Thanks for listening, for Scientific American 60-Second Science. I'm Karen Hopkin.
感谢您对科学美国人60秒科学的倾听。我是凯伦霍普金。