How Did Humans Change a Wolf to a Dog?人类是如何将狼变成狗的？

Most pet owners probably know what it’s like to cave to those “puppy dog” eyes—no matter the age of their canine1. When your dog looks at you with that curled brow and doleful stare， it’s difficult not to give it a loving scratch or meaty treat2. And why not： You and your furry friend have been conditioned3 by thousands of years of evolution for this moment， according to a growing body4 of research by biological anthropologists like Anne Burrows.

大部分养宠物的人可能都了解向“狗狗眼”屈服的感觉——无论狗狗年龄有多大。当狗狗皱着眉，忧郁地望向你，你很难不去给它一个爱的挠挠，或者请它吃肉肉大餐。何乐而不为呢？你和毛孩子历经数千年的进化，才成全了这一时刻。越来越多的生物人类学家——像安妮·伯罗斯等——的研究为此提供了佐证。

“Dogs are our closest companions，” she says. “They’re not closely related to us [as a species]， but they live with us， they work with us， they take care of our children and our homes. So investigating different aspects of the dog-human bond， I thought， would help me understand human evolution and human origins.”

“狗是我们最亲密的伙伴。”她说，“（从物种上来说，）它们并非人类的近亲，却与我们共同生活，一起工作，看护我们的孩子和家园。所以我认为，研究人犬关系的各个方面，能帮助我了解人类的进化和起源。”

From disarming5 looks to alarming barks， Burrows and her team at Duquesne University in Pittsburgh investigate the ways dogs have evolved to express themselves in order to earn the title of “man’s best friend.” The research group is taking a detailed anatomical6 approach to understand how dogs and their wild relatives， wolves， evolved to have different traits， such as facial expressions and vocalizations7.

从让人卸下防备的表情到令人不安的吠叫，来自宾夕法尼亚州杜肯大学的伯罗斯及其团队探究了狗为赢得“人类最好的朋友”这一美名，而进化出的自我表达方式。研究团队采用了一种细致的解剖学方法，来研究狗和它那野生的近亲狼是如何进化出不同特性的，比如各种面部表情和声音。

The ancient relationship between people and canine companions can give anthropologists a window into human evolution， says Burrows. The timing is still contested8， but some 15，000 to 35，000 years ago， early Homo sapiens in parts of Europe and Siberia began to change their relationship with local wolf populations9. One theory to how that started is that a few bolder wolves began to cooperatively hunt with people for larger land game10， allowing increased success for both parties. Another is that nomads left behind remains from butchered mammals that wolves would then dine on， causing the canines to become more domestic11 （but scholars have widely debated this narrative）. “It could be something completely different， but the main hypotheses are that it somehow involved food，” says Burrows. Looking at the evolution of dogs in the context of these millennia-old interactions can show how human ancestors lived and survived in the past.

伯罗斯说，历史悠久的人犬关系是一扇窗户，人类学家能借此一窥人类进化。虽然具体时间尚有争议，但大约在1.5万至3.5万年前，生活在欧洲和西伯利亚部分地区的早期智人，就已经开始改善与当地狼群的关系。至于是如何开始的，一个理论认为，一些胆子较大的狼开始与人类合作，狩猎体型更大的陆地动物，从而提高双方的成功率。而另一个理论认为，狼进食了游牧民宰杀哺乳动物后留下的残骸，因此变得更为驯化（不过，此观点引起了学者的广泛争论）。“情况可能完全不同，但主流的假说都认为，这多少都与食物有关。”伯罗斯说。在数千年的人犬互动中观察狗的进化，我们能看见人类祖先在过去是如何生活和生存的。

Burrows decided to focus on how dogs communicate with humans through their faces—a unique trait that’s rare between unrelated species， she says. This was inspired by her previous work studying facial muscles in primates. Chimps have displayed the ability to understand the facial expressions of other members of their species， similar to how humans depend on faces for context clues. In 2019， Burrows decided to hunt for similar signals between humans and dogs， and compare them to wolves. “Whether we know it or not， dogs and humans are constantly looking at one another’s face， and trying to understand what the other one is feeling， and what the other one intends，” Burrows says. “So， facial expression is our proxy12 for understanding the relationship between dogs and humans.”

伯罗斯决定重点研究狗是如何使用面部与人类沟通的。她认为，这种独特的沟通方式在两个没有亲缘关系的物种之间实属罕见。该研究方向是受她从前对灵长类动物面部肌肉研究的启发。黑猩猩表现出能够理解其他同类面部表情的能力，与人类察言观色相似。2019年，伯罗斯决定寻找人犬之间的类似表情信号，并将其与狼做对比。“不论我们是否意识到，狗和人都在不断观察彼此的脸，尽力了解对方的感受和意图，”伯罗斯说道，“所以，我们能通过面部表情这个指标，来理解人犬关系。”

Previous studies have demonstrated that dogs can read and respond to human facial expressions—and even synchronize their emotions to match. “Dogs are watching us very closely—some of this is based on our gaze and body language， but also on the sounds we make and the scents we give off，” Monique Udell， an animal behaviorist and associate professor of animal sciences at Oregon State University in Corvallis， told National Geographic in 2021. Another study in July 2021 in the journal Current Biology found that dog puppies make more eye contact with humans than wolves， even when the wolf pups were reared by humans nearly from birth.

过去的研究已经证明，狗能够读懂人类表情并做出反应，甚至能调整自身情绪与之呼应。莫妮克·尤德尔是一名动物行为学家，在科瓦利斯的俄勒冈州立大学任动物科学副教授，2021年时她告诉《国家地理》杂志：“狗对我们的观察很细致，其中，有些观察是基于我们的眼神和身体语言，有些则是根据我们的声音和散发的气味。”2021年7月，另一篇发表在《当代生物学》杂志上的研究表明，相较于幼狼，幼犬与人类的眼神接触次数更多，即便和那些几乎生来便被人类抚育的幼狼相比，也同样如此。

The evolutionary differences could be explained by fine-grained13 face muscles in both wolves and dogs. Burrows， along with collaborators Juliane Kaminski and Bridget Waller， found that a large range of dog breeds had defined musculature around the eye that lifts the brow up. The wolves they studied did not have the same attribute. This suggests that as humans domesticated wolves， they selected individuals with friendlier behaviors and traits， like a persuasive brow raise or smaller teeth and snouts. Since publishing these findings， Burrows has continued to collect data on other muscles that control facial expressions， known as mimetic muscles. “We know dogs’ facial expressions， but we don’t really know how their muscles work in the actual contractions，” she explains.

狼和狗的面部肌肉细密纹理可以解释二者的进化差异。伯罗斯与其合作者朱利安娜·卡明斯基和布里奇特·沃勒发现，许多犬种的眼周都分布着清晰的肌肉组织，让狗能够抬起眉毛。而他们研究的狼却没有该特征。这说明人类在驯化狼的过程中，选择了在行为和特性上更为友好的个体，例如，能够令人信服地扬眉，拥有更短的牙齿和鼻子。这些研究成果发表后，伯罗斯继续收集其他控制面部表情的肌肉（即表情肌）的数据。“我们能读懂狗的面部表情，但它们面部肌肉的实际收缩机理，我们还没弄明白。”她解释道。

Humans mostly have fast-twitch muscles14 in their faces， but do have more slow-twitch muscles15 than chimpanzees， likely in part to form sounds for speech， Burrows says. Currently， her group is applying this reasoning16 and methodology to dog and wolf muscles by looking at the amount of fast- and slow-twitch fibers that control the duration and speed of contractions. Fast-twitch fibers allow for more spontaneity， but also tire more easily （think of smiling for a long period of time）; slow-twitch fibers take longer to start contracting， but are better for endurance （think of sustained walking or running）.

人类脸上的肌肉以快缩肌为主，但相较于黑猩猩，人类脸上的慢缩肌仍旧要多一些，部分原因可能是人类需要发声讲话，伯罗斯说。她的团队正将此推断和方法应用于狗和狼的肌肉研究中，即关注快缩型肌纤维和慢缩型肌纤维的数量。这两种肌肉纤维控制肌肉收缩的时长和速度，快缩型肌纤维的自发性更强，但也容易疲惫（试想一下长时间微笑），而慢缩型肌纤维的启动时间较长，耐力却更好（如长时间走路或长跑）。

For their latest research， Burrows and her graduate students sampled cross sections of facial muscles in humans， dogs， and wolves and determined the amount of each fiber type. Burrows notes that the sample size of the preliminary data is small， with six wolf specimens and 10 specimens of different dog breeds. From this initial data， the team expected that the muscle profiles of dogs and humans would look similar， while the wolves would be distinct. However， they found that humans and wolves were actually more alike with more slow-twitch fibers overall， while dogs had more fast-twitch fibers.

在最新的研究中，伯罗斯及其研究生对人、狗、狼的面部肌肉横截面进行了采样，并测定了每种肌肉纤维的数量。伯罗斯指出，初步数据的样本量很小，只有6只狼和10只品种不同的狗。根据这个样本数据，研究团队曾预测人和狗的肌肉剖面会相似，狼则不同。然而他们发现，实际上人和狼才更相似，二者面部以慢缩型肌纤维为主，而狗脸上却是快缩型肌纤维居多。

“At first we were horrified，” says Burrows. “But as we thought about what muscle fibers of the face do， it kind of began to make a little bit more sense. Humans use speech， and that means we have to slow down our lips so that we can clearly articulate speech sounds. Wolves use howling and it’s a protracted vocalization—they kind of make a funnel out of their lips.” Meanwhile17， a dog’s bark is a much shorter vocalization， so it doesn’t require them to hold their lips in one position for an extended amount of time.

“最初我们都被吓到了，”伯罗斯说，“但考虑到面部肌肉纤维的作用，这就开始有点道理了。人要说话，意味着我们要放慢唇动频率才能清晰地发音。狼嚎叫，要拖长声音，就得把嘴撅成漏斗形。”然而，狗的吠叫要短促得多，因此狗不需要长时间保持一定幅度的张嘴。

The findings have led Burrows to suspect that humans may have favored wolves that had shorter staccato18 vocalizations during the process of dog domestication. Anthropologists have suggested that as humans domesticated dogs， they sought animals that could guard or warn them of any sudden threats. This alarm call—or bark—could have been important in the process of dog domestication. Now， “dogs just bark for a living，” Burrows says.

根据这些发现，伯罗斯猜测，在驯化过程中，人类或许倾向于选择叫声更为短促刺耳的狼。人类学家认为，人类驯化狗时，寻找的是能保护自己，或对突发威胁预警的动物。这种警报声，也就是吠叫，在狗的驯化过程中可能很重要。而如今，“狗吠叫只是为了讨生活。”伯罗斯说。

And while both animals do exhibit a range of vocalizations， they have a tendency to stick to their specific styles， Burrows says. Wolves only bark occasionally when they want to alert a nearby pack. And with the exception of certain breeds like huskies and hounds， dogs are much less partial to howls. “We seem to have kind of created this weird creature， this dog that uses vocalizations very differently than the way wolves use them，” Burrows explains.

伯罗斯表示，虽然狼和狗都展现出一系列不同的发声方式，但他们却倾向于保持特定的发声风格。狼很少吠叫，只在想要警示附近狼群时才这么做，至于狗，除了哈士奇和猎犬等特定犬种，都不爱嚎叫。“某种程度上，似乎是我们造就了狗这种奇异的生物，它们使用嗓音的方式和狼截然不同。”伯罗斯解释道。

The team is planning on completing another year’s worth19 of data collecting before publishing their next study. Personally， Burrows would like to investigate how the facial muscles of ancient dog breeds， like huskies， malamutes， and chow chows， compare to wolves， as well as younger dog breeds. The older breeds might be able to help anthropologists really break down the relationships that turned wolves into dogs.

该团队打算在下一项研究成果发表前，先完成另一个年度的数据收集工作。就个人而言，伯罗斯想研究哈士奇、爱斯基摩犬、松狮犬等古老犬种的面部肌肉，将其和狼以及其他更为近代的犬种进行对比。古老的犬种或许能够帮助人类学家真正破解使狼变成狗的人犬关系之谜。

“Our evolutionary history of becoming human is intimately tied to the process of dog domestication，” Burrows says. “When we look at a dog today， we see what was important to Upper Paleolithic20 people， 30，000-plus years ago. Dogs just get us in a way that no other animal does.”

“我们变成人类的进化史，与狗的驯化史密切相关。”伯罗斯说，“今天我们看着狗，能看到三万多年前对旧石器时代晚期人类来说意义重大的东西。狗狗拿下我们的方式，是其他动物无法比拟的。”

（译者为“《英语世界》杯”翻译大赛获奖者）

1 canine 〈正式〉犬，狗。 2 treat款待。 3 condition使适应，使有准备。 4 body 大量。

5 disarming使人消除戒心的。 6 anatomical解剖的；（人体或动物体）结构上的。 7 vocalization发出的声音。 8 contest争辩，就……提出异议。 9 population动物种群。 10 game猎物。 11 domestic驯养的。

12 proxy指标。

13 fine-grained纹理细密的。

14 fast-twitch muscle快缩肌。 15 slow-twitch muscle慢缩肌。 16 reasoning推理。

17 meanwhile与之相比，对比之下。 18 staccato（声音）短促刺耳的。

19 worth持续的时间。 20 Upper Paleolithic旧石器时代晚期的，upper指地质或考古中“晚期的，较近期的”。