But they didn't do it alone.

但人類並非靠自己單打獨鬥。

Whatever corner of the globe you find homo sapiens in today, you're likely to find another species nearby: canis lupus familiaris.

在今日的地球上，只要是有智人的地方，通常都會有另一個物種：犬。

Whether they're herding, hunting, sledding, or slouching, the sheer variety of domestic dogs is staggering.

無論是在放牧、捕獵、拉雪橇或是在一旁閒閒沒事，家犬的種類真的是驚人地多。

But what makes the story of man's best friend so surprising is that they all evolved from a creature often seen as one of our oldest rivals: canis lupus, or the gray wolf.

但更令人驚訝的是，人類最好的朋友其實源自於我們老祖宗的死對頭：灰狼。

When our Paleolithic ancestors first settled Eurasia roughly 100,000 years ago, wolves were one of their main rivals at the top of the food chain.

當我們舊石器時代的祖宗在大約十萬年前定居歐亞大陸時，狼是他們在食物鏈頂端的主要敵手之一。

Able to exert over 300 lbs. of pressure in one bone-crushing bite and sniff out prey more than a mile away, these formidable predators didn't have much competition.

這些強大的獵食者咬合力多達 136 公斤，足以一口咬碎骨頭，並且能夠在 1.6 公里外就聞到獵物的氣味，可說是無可匹敵。

Much like human hunter-gatherers, they lived and hunted in complex social groups consisting of a few nuclear families, and used their social skills to cooperatively take down larger creatures.

和人類狩獵採集者類似的是，牠們也有核心家庭組成的複雜社會結構，生活和捕獵方式都在其框架下，並且利用社交技能合作打下大型獵物。

Using these group tactics, they operated as effective persistence hunters, relying not on outrunning their prey, but pursuing it to the point of exhaustion.

藉由這些群體策略，牠們成為了成功的長跑獵食者，不靠跑得比獵物快，而是靠將獵物追到筋疲力盡。

But when pitted against the similar strengths of their invasive new neighbors, wolves found themselves at a crossroads.

但是當面臨擁有類似本領的新鄰居時，灰狼迎來了做抉擇的時刻。

For most packs, these burgeoning bipeds represented a serious threat to their territory.

對大多數狼群而言，這些新興的兩足動物就等同於對領土莫大的威脅。

But for some wolves, especially those without a pack, human camps offered new opportunities.

但對於一些狼，尤其是那些離群索居的，人類社群意味著新的機會。

Wolves that showed less aggression towards humans could come closer to their encampments, feeding on leftovers.

對人類較沒攻擊性的狼會靠近他們的營區，撿食他們的廚餘。

And as these more docile scavengers outlasted their aggressive brethren, their genetic traits were passed on, gradually breeding tamer wolves in areas near human populations.

當這些個性較溫順的清道夫活得比他們好鬥的兄弟們久時，他們的基因特質就會繁衍下去，逐漸在人類群居地附近孕育出較溫馴的狼群。

Over time humans found a multitude of uses for these docile wolves.

隨著時間過去，人類發現這些溫馴的狼有許多用途。

They helped to track and hunt prey, and might have served as sentinels to guard camps and warn of approaching enemies.

牠們幫助追蹤並獵捕獵物，或許也曾經當過守衛保護營地、提醒人們有敵人逼近。

Their similar social structure made it easy to integrate with human families and learn to understand their commands.

牠們類似於人類的社會結構讓牠們更容易融入人類家庭，並學習理解指令。

Eventually they moved from the fringes of our communities into our homes, becoming humanity's first domesticated animal.

最終，牠們從社會邊緣進到我們的家中，成為人類首次馴養的動物。

The earliest of these Proto-Dogs or Wolf-Dogs, seem to have appeared around 33,000 years ago, and would not have looked all that different from their wild cousins.

最早的原始狗，或稱狼狗，似乎是出現於大約三萬三千年前，而且外表和他們野外的親戚沒多大差別。

They were primarily distinguished by their smaller size and a shorter snout full of comparatively smaller teeth.

牠們主要的不同在於身形比較小，而且口鼻比較短，牙齒也相對較小。

But as human cultures and occupations became more diverse and specialized, so did our friends: short stocky dogs to herd livestock by nipping their heels; elongated dogs to flush badgers and foxes out of burrows; thin and sleek dogs for racing; and large, muscular dogs for guard duty.

但隨著人類文化和職業變得更多元、專精，我們的朋友也是：矮胖結實的狗藉由輕咬家畜的腳踝幫忙放牧，身形長的狗把獾和狐狸趕出洞穴，纖細光滑的狗專門賽跑，還有巨大魁梧的狗負責守衛。

With the emergence of kennel clubs and dog shows during England's Victorian era, these dog types were standardized into breeds, with many new ones bred purely for appearance.

於英國維多利亞時代出現養犬俱樂部和狗展後，這些狗被標準化為不同品種，還有許多新品種是純粹為了外觀而繁殖。

Sadly, while all dog breeds are the product of artificial selection, some are healthier than others.

難過的是，雖然所有狗的品種說來都是人類篩選的結果，一些品種的健康狀況卻不如其他。

Many of these aesthetic characteristics come with congenital health problems, such as difficulty breathing or being prone to spinal injuries.

許多美觀特質其實都伴隨先天的健康疾病，例如呼吸困難或是脊椎較容易受傷。

Humanity's longest experiment in controlled evolution has had other side effects as well.

人類長期以來控制演化也帶來了其他副作用。

Generations of selection for tameness have favored more juvenile and submissive traits that were pleasing to humans.

世代對於馴養的篩選偏好較為年幼、順從的特質，這些都為人類所愛。

This phenomenon of selecting traits associated with youth is known as neoteny, and can be seen in many domestic animals.

這種篩選年幼特質的現象稱為「幼態延續」，在許多家畜身上都有跡可循。

Thousands of years of co-evolution may even have bonded us chemically.

幾千年來的共同演化，甚至有可能使我們產生化學方面的連結。

Not only can canines understand our emotions and body language, but when dogs and humans interact, both our bodies release oxytocin, a hormone commonly associated with feelings of love and protectiveness.

犬科動物不僅能夠懂我們的情緒和肢體語言，而且當狗和人類接觸時，雙方的身體都會釋放催產素，一種通常會和愛還有保護感聯繫在一起的荷爾蒙。

It might be difficult to fathom how every Pomeranian, Chihuahua, and Poodle are descended from fierce wolves.

博美犬、吉娃娃和貴賓犬的祖先竟然是兇猛的狼，這或許令人難以理解。

But the diversity of breeds today is the result of a relationship that precedes cities, agriculture, and even the disappearance of our Neanderthal cousins.

但今日有那麼多品種的狗，正是因為在早於城市出現、農業發展、甚至是尼安德特人消失之前，人和狗結下了一段緣分。

And it's heartening to know that given enough time, even our most dangerous rivals can become our fiercest friends.

振奮人心的是，只要有足夠的時間，即使是我們最危險的死敵，都能成為我們的好友！