PBS.新星.狗狗的起源与演化（2004）

doesn't need much of a brain.
寻找腐烂的番茄吃
I mean it doesn't take a lot of cunning
不用费多少脑筋
to figure out where a rotten tomato is.
只要有人扔番茄的时候
You basically have to be there
跑过去捡就行了
when somebody throws the tomato away.
基本上就是守株待兔
So you're kind of a sit and wait animal.
是人类的残羹剩菜
Was it the lure of our leftovers
导致了狼的驯化吗
that ushered in the era of animal domestication,
还是由于人类出于喜爱而驯化它们
or was it a matter of puppy love?
不管怎样 关键就是
Either way, what's critical is
如果比其它同类更温顺
that tamer than average individuals
在繁殖后代上优势也就越大
somehow gain an advantage and become more likely to breed.
但是这仍无法解释另一个问题
Of course, that leaves unanswered another problem.
很多狗的耳朵松软下垂
Many dogs have floppy ears,
尾巴向上卷曲
tails that turn up and curl,
斑点花色各不相同
patchy coats of many colors.
这些性状并没有出现在狼身上
These aren't things you see on wolves, which makes sense
这些对狼的生存没有任何帮助
because none of them would help a wolf survive in the wild.
有人认为
It's been suggested that
人类驯养狗时 有意挑选了这些性状
humans consciously bred for these traits.
雷·柯平格认为这种说法更是荒诞至极
Ray Coppinger thinks that's more nonsense.
难道你会专门去选择一种尾巴
What do you do? Do you start selecting for a tail?
让狗的尾巴一代比一代
You know—each generation of tail is going up
往上翘一点 直到变成现在这样
inch by inch until it gets to the top.
与此同时 耳朵一代比一代下垂
And while the tail is going up the ears are coming down
直到完全耷拉下来
centimeter by centimeter until they're floppy ears.
遗传学上来讲 必然有一种机制
From a genetic point of view, I've got to have a mechanism,
肯定是某种机制 导致了这种现象发生
I've got to have something there, and believe it or not,
一直以来 这都是个未解之谜
for forever it's been a mystery.
所有的生理特征
Traits like coat color,
毛色 耳朵或尾巴的位置
or the way a dog carries its ears or tail,
都是由基因决定的
are determined by its genes.
基因是DNA的片段
Genes are pieces of DNA,
不同基因之间存在细微差别
and they often come in subtly different versions.
每只狗的基因都是
Every dog gets one copy of every gene
一半来自于妈妈 另一半来自于爸爸
from mom and one from dad.
这些基因之间可以有无数种组合
These genes can be mixed and matched in countless ways,
但若父母没有这份基因
but if the parents don't have it,
小狗也无从获得
the pup can't get it.
这让狗狗们斑驳的毛色
And that's what makes curly tails
和向上卷曲尾巴的形成过程变得神秘
and patchy coats in dogs so mysterious.
因为它们的祖先狼 并不具有这些特征
Wolves don't have them.
在一个意想不到之地的一个神奇实验
It took a remarkable experiment in a most unlikely place,
揭开了这个谜题的神秘面纱
to solve this mystery.
实验地点就在西伯利亚一个偏僻之地
The place was the middle of nowhere, Siberia.
实验者是一名过气的俄♥国♥遗传学家
And the experimenter was an out-of-favor Russian geneticist
德米特里·巴里耶夫
named Dmitri Belyaev.
当地的狐狸养殖场主请巴里耶夫帮忙
Local fox farmers had asked Belyaev for help
培育一些更温顺的动物
in breeding a less vicious animal.
巴里耶夫从他找到的最温顺的狐狸入手
Belyaev began with the tamest foxes he could find.
再从它们的子孙后代中
From their offspring, and for many generations thereafter,
挑选最温顺的继续繁殖
he chose only the tamest for breeding.
他认为这些狐狸的攻击性
He'd expected that each new generation
会一代代逐渐减弱
would be a little less vicious, a little more tame.
但培养到第十代时
But by the tenth generation,
出乎意料的事情发生了
he was seeing things he'd never expected.
突然之间 狐狸的耳朵耷拉下来了
All of a sudden his fox ears started down,
尾巴开始往上翘 它们开始吠叫
his fox tails started up, they started to bark,
这些都不是狐狸原有的特征
which is not characteristic of foxes.
它们开始有各种不同的毛色
They started to have different coats,
之前根本没有人能想到
all these little features
这些体征会出现在野生动物身上
that you can't imagine being in the wild type.
并没有人特别去选择它们
I mean it's not a matter of selecting for,
因为根本就没什么好选的
because they're not there to be selected for
之前并没有变异出现
that variation isn't there.
温顺个性和下垂耳朵之间有何联♥系♥
What does tameness have to do with ears,
和吠叫以及毛色又有什么关系
and barking and coat color?
巴里耶夫和他的同事们
Belyaev and his colleagues
随即开始了对这些问题的探索
immediately went looking for an explanation.
他们检查了这些狐狸的肾上腺素水平
They checked the foxes' adrenaline levels—
肾上腺素能控制
that's the hormone that controls
动物在外界刺♥激♥下的应激反应
the "fight or flight" response
结果这些狐狸的肾上腺素远低于普通狐狸
and they found they were far lower than normal.
这可以解释它们的温顺性格
That would explain the tameness,
它们肾上腺素不足
they're just not afraid because
所以它们不感到恐惧
they're not producing as much adrenaline.
但斑驳的毛色又从何而来
But where does the multi-colored coat come from?
有人马上就反应过来
And somebody says right off the bat,
肾上腺素在黑色素的合成途径中
"Hey, adrenaline's on a biochemical pathway
也占有一席之地
that also goes to melanin,
黑色素和毛色肯定相关
also has something to do with the animal's coat color."
这就建立了肾上腺和毛色之间的联♥系♥
So there's a correlation between coat color now and the adrenal gland.
突然之间 一切都变得合情合理
Suddenly, it all started to make sense.
巴里耶夫培育温顺狐狸的过程中
As Belyaev bred his foxes for tameness,
狐狸们的激素水平
over the generations their bodies began producing
一代不同于一代
different levels of a whole range of hormones.
而这些激素水平
These hormones, in turn,
导致了一系列的下游反应
set off a cascade of changes
从而产生了各种不同的遗传变异
that somehow triggered a surprising degree of genetic variation.
仅仅依靠这种选择温顺动物
Just the simple act of selecting for tameness
就打破了动物原有的基因组合
destabilized the genetic make up of these animals
从而导致
in such a way that all sorts of stuff
一些野生种群不曾拥有的新体征
that you would never normally see in a wild population
突然出现
suddenly appeared.
大部分犬类生物学家都认为
Most dog biologists now believe something very similar to
和对待这些狐狸一样
what happened to these foxes
早在一万多年前
also happened to a population of wolves
人们对狼群也进行了同样的选择
more than 10,000 years ago.
也有人说这是大自然的选择
And the rest, as they say, is history:
人类驯服的第一种动物
the world's first domestic animal.
从它们出现的那天起
And from the beginning,
狗就对人类社会极其适应
dogs have been a remarkably good fit in human society,
这要多亏它们从狼那里遗传来的社会技能
thanks in large part to the social skills they inherited from wolves.
我认为关键在于
The key thing, I think,
狗在被驯化之前
was that dogs are pre-adapted to living
就已经适应了复杂的社会群体化生活
in fairly complicated social groups.
狼群一般都有着
Wolf society typically has quite well-established
严格固定的等级制度
dominance hierarchies within it.
每个个体都要学会在这种等级制度下生存
Individuals learn to slot themselves into that hierarchy
并履行各自的职责
and function within that context.
下级的狼很善于
Low-ranking wolves are adept at sucking up
讨好其强大的同伴
to their more powerful pack mates.
狗则把这些技能用在了人身上
Dogs use many of those same skills with people.
狗给我们传达了这样的信息
So we're getting these signals from our dogs
我们很重要
that we are important,
它爱我们 我们是世界上最重要的
we're loved, we're the greatest thing around.
对我来说
And you know, to me,
这就是我们喜欢狗的原因
it's obvious why we like dogs
因为它们很擅长表达对我们的喜爱
because they're so good at showing that they like us.
人与狗之间这种亲密的关系
This intimate bond between humans and dogs
根据一个颇受争议的理论
goes back a long way
可以追溯到很久很久以前
according to one controversial theory, a very long way.
珍妮弗·伦纳德是加州大学洛杉矶分校
Jennifer Leonard is part of a team at UCLA
古DNA研究小组中的一员
that studies ancient DNA.
她正前往伦敦自然历史博物馆
She's come to London's Natural History Museum
搜集一些古代狗的骨头
to collect some really old dog bones
她希望能够通过这些骨头
which she hopes will help prove
证明他们小组的新理论
the team's radical new theory.
这是一些残存的家犬骨头
These are some domestic dog remains.
来自前陶器时代[距今约9500～8000年]
They date to the pre-pottery Neolithic period.
一小片六千年前的狗牙同样含有DNA