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Why the Cross Put Chickens on a New Road 探秘家禽的驯化之路

Why did the chicken cross the road? Well, that’s a philosophical¹ pickle². 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.

为什么鸡要过马路?这是一个哲学问题。但是，如果你想知道为什么鸡不会生人类的气，为什么它们甘愿被困在笼子里——科学可以帮你找出答案。

“Domestic species are interesting because their genetic⁴ makeup⁵ has changed dramatically as part of the process of going from wild to domestic.”

“家养物种之所以有趣，是因为它们的基因组成在从野生到家养的驯化过程中发生了翻天覆地的变化。”

\Liisa Loog, an evolutionary⁶ geneticist and anthropologist⁷ at the Universities of Oxford⁸ and Cambridge.

莉萨·莱格——牛津大学和剑桥大学的一名进化遗传学家和人类学家。

“And indeed when people have compared modern domestic animals with their wild relatives they’ve identified genes⁹ that do show signs of strong recent selection. One such gene³ is thyroid stimulating¹⁰ hormone¹¹ receptor, otherwise known as TSHR…in chickens, a variant¹² 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 aggression¹³ towards conspecifics.”

“的确，当人类将现代家畜与它们的野生亲属进行比较时，发现基因确实有明显的近期选择的迹象。促甲状腺激素受体(TSHR)就是在鸡身上发现的这样一个基因……该基因的一个变体普遍存在于现代家养鸡群中，且已被证明是它直接导致了家养鸡不会害怕人类，也是它导致了家养鸡对同种个体的攻击性变弱。”

But when exactly did the selection for these traits—and therefore this variant—take place?

但是这些特性的选择以及这种变体到底是什么时候发生的呢?

“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 domesticated¹⁴ around 6,000 years ago in East Asia. 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…but with DNA¹⁵ from archaeological material we can follow what happened with a gene through time and in theory spot when changes in a population occur.”

“由于这些特性在家养环境中存在潜在用处，因而这种基因选择极有可能发生在约6000年前，鸡类首次在东亚被驯养之时。但在进化时间表中这就是一眨眼的事儿，我们无法仅利用现代鸡类的数据就清楚地分辨出这种基因选择是在6000年间的具体何时发生的……但是，通过从考古材料中提取的DNA，我们可以推断出基因在时间长河中发生了什么变化，以及从理论上讲一个种群何时发生了变化。”

Loog and her colleagues examined TSHR gene sequences in the ancient remains¹⁶ of about 60 chickens found in Europe “and estimated that selection at this TSHR locus¹⁷ happened only around 1,000 years ago, at medieval times. That is, 5,000 years after the initial domestication¹⁸ of chicken.

莱格和同事们研究了在欧洲发现的约60只古代鸡的遗骨中的TSHR基因序列，“据估计TSHR基因选择仅发生在大约1000年前中世纪时代，即鸡类被驯养了5000年后。”

“Interestingly this time period coincides with a…substantial increase in chicken consumption known from the archaeological record. Historians suggest that a key driver behind these changes was the rising popularity and spread of Christian¹⁹ traditions, which discouraged and also on occasions even banned eating meat from four-legged animals.”

“有趣的是，从考古记录中可见这一时期正值……鸡肉消费大幅增加之时。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，这些传统劝阻人们、有时甚至会禁止人们食用来自四足动物的肉食。”

But fowl²⁰ were fair game.

而家禽类却是允许被捕食的。

“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. The findings appear in the journal Molecular²¹ Biology and Evolution.

“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基因变化与人类食物偏好的文化转型联系起来。”这一发现发表于《分子生物学与进化学》杂志。

This kind of plucky²² study is not just for the birds. Loog says the team is collecting canine²³ archaeological samples, so they can look at how man’s best friend got divvied up into so many different breeds. Their research will no doubt be dogged.

这种大胆的研究不仅仅是针对家禽类。莱格表示她们团队正在收集犬类的考古样品，准备研究人类最好的朋友是如何被分为这么多不同品种的。他们的研究无疑会遭遇困扰。