我們和我們的寵物是怎樣共同進化的

DAVIS, Calif. — IT’S commonplace to call our cats “pets.” But anyone sharing a cat’s household can tell you that, much as we might like to choose when they eat in the morning, or when they come inside for the night, cats are only partly domesticated.

加利福尼亞州戴維斯——我們的貓通常被稱爲“寵物”。但任何一個跟貓共同生活的人都會告訴你，我們雖然很想決定它們早上進食或者晚上進屋的時間，但它們並沒有被完全馴化。

The likely ancestors of the domestic dog date from more than 30,000 years ago. But domestic cats’ forebears join us in the skeletal record only about 9,500 years ago. This difference fits our intuition about their comparative degrees of domestication: Dogs want to be “man’s best friend”; cats, not so much.

家犬的祖先可能出現於3萬多年以前。但骨骼化石記錄表明，家貓的祖先遲至大約9500年前才進入人類社會。這一差距與我們對兩種動物馴化程度差異的直觀感受是一致的：狗想成爲“人類最好的朋友”，貓則不然。

Fossils are handy snapshots of the past, but a genomic sequence is a time machine, enabling scientists to run evolutionary history backward. The initial sequence of the domestic cat was completed in 2007, but a recent study to which I contributed compared the genomes of the domestic cat and the wildcat (Felis silvestris) and sheds new light on the last 10,000 years of feline adaptations.

如果說化石是現成的歷史縮影，那基因組序列就是一臺時光機，讓科學家得以追溯進化的歷程。對家貓基因的初步測序是在2007年完成的。但最近，我參與的一項研究比較了家貓和野貓(Felis silvestris)的基因組，可以讓人們更好地瞭解貓在過去1萬年間適應環境的過程。

Domestic cats are not just wildcats that tolerate humans in exchange for regular meals. They have smaller skulls in relation to their bodies compared with wildcats, and are known to congregate in colonies. But in comparison with dogs, cats have a narrower range of variation in size and form.

家貓不僅僅是爲了規律飲食，而勉強和人類呆在一起的野貓。與野貓相比，它們頭骨與軀幹的比例更小；而且衆所周知，它們會集羣而居。但和狗相比，不同種類的貓在大小和外形上的差異不是太大。

Wesley C. Warren, an author of the study, notes that domestic cats have excellent hunting skills, like their wild ancestors. This, too, supports the notion that cats are only semi-domesticated.

研究報告的執筆者之一韋斯利·C·沃倫(Wesley C. Warren)指出，家貓和它們生活在野外的祖先一樣，有出色的狩獵技能。這就爲家貓只是半馴化動物的觀點提供了支撐。

Comparing the genomes of the wildcat and the domestic cat added much to what we had known. Michael J. Montague, the lead author, told me he’d anticipated that the two genomes would be very similar, but our study found a specific set of differences in genes involved in neuron development. This brain adaptation may explain why domestic cats are docile.

比較野貓和家貓的基因組，讓我們的既有認知有了極大的拓展。研究報告的第一作者邁克爾·J·蒙塔古(Michael J. Montague)告訴我，他曾經預計兩者的基因組會非常相似，但我們在研究中發現了一組涉及神經元發育的特定基因。這種大腦的適應，或許可以解釋爲什麼家貓比較溫順。

Scientists have long observed that domesticated species exhibit a suite of strikingly similar traits, from floppy ears to smaller brains, than those of their wild ancestors. Domestication may select for a few similar traits encoded by genetic changes (like smaller brains), but these may produce what we assume are secondary effects (like floppy ears).

科學家早就發現，家養物種有着一系列極爲相似的特徵，如軟趴趴的耳朵，以及比野生祖先小的大腦。馴化過程可能會選擇一些由基因差異決定的相似特徵（如較小的大腦），但這些基因可能又會帶來我們眼中的次生效應（如軟趴趴的耳朵）。

Once they were living among us, cats didn’t need to think so much to stay alive; nor did they need such large jaws after we started feeding them our processed scraps. Hence smaller skulls. The same dynamic holds for dogs: Wolves beat dogs in general intelligence tests.

自從和人類生活在一起，貓要生存下去就不需要思考那麼多了；以人類的殘羹剩飯爲食，它們也不再需要大大的下巴了。因此，它們的頭骨變小了。狗也是如此：狼在智力測試中的表現通常好於狗。

By examining patterns in our animals’ genomes, we’ve confirmed that the same sets of genes seem to be targeted again and again in evolution. As far back as Charles Darwin, domestic animals in particular have yielded insights about evolution because we know what sorts of selection pressures they were subject to. After all, it was us they were primarily adapting to.

我們通過觀察家養動物的基因組圖譜確定，在進化過程中，某些特定的基因一再成爲選擇的目標。早在查爾斯·達爾文(Charles Darwin)的時代，對於家養動物的研究，就幫助拓展了人類對進化過程的認識，因爲我們很清楚它們面臨着怎樣的選擇壓力。畢竟，它們主要是在適應人類。

Which brings us to the genome of one critical tame animal: ourselves, humans. The Nobel Prize-winning zoologist Konrad Z. Lorenz once suggested that humans were subject to the same dynamics of domestication. Our brain and body sizes peaked during the end of the last ice age, and declined with the spread of agriculture.

作爲一種重要的馴化動物，人類自身的基因組也是進化過程的產物。獲得過諾貝爾獎的動物學家康拉德·Z·洛倫茨(Konrad Z. Lorenz)曾表示，人類也受制於同樣的馴化機制。我們大腦和軀幹的尺寸在最後一個冰川時代結束時達到最高點，繼而隨着農耕的推廣逐漸變小。

Instead of poring over the meager fossil record, we can survey patterns of variation across tens of thousands of living individuals. Genomics now provides evidence that humans have been subject to a great deal of natural selection over the past 10,000 years. A beautiful example is the ancestors of Tibetans’ absorption of small portions of the genome of ancient human relatives adapted for living at high altitude.

我們不必去鑽研匱乏的化石記錄，而是可以研究千千萬萬活人的基因差異。目前，基因組學方面的證據表明，人類在過去1萬年裏一直受到了自然選擇的極大影響。一個有力的例子是，西藏人的祖先汲取了少量與其有親緣關係的適應高海拔生存的古人類的基因。

Our cultural flexibility and creativity since the end of the ice age have not freed humans from evolutionary forces, but have opened up novel and startling paths. Thinking of domestication as an evolutionary process that occurs through “artificial” selection creates a false dichotomy of nurture and nature that plays into a conceit of human exceptionalism. In fact, the idea that we are apart from nature, that it is ours to tame and exploit, is an outmoded approach.

最後一個冰川時代結束以來，人類的文化適應性和創造力並沒讓我們擺脫進化力量的影響，而是爲這種力量開闢了令人吃驚的新路徑。把馴化當成由“人工”選擇推動的進化過程，讓人們錯誤地把自然過程和馴化過程分割開來，由此催生出自負的人類例外論。認爲人類與自然相分離、人類要馴化和開發自然，其實是一種過時的思維。

A more useful interpretation is that over the past 10,000 years, humans fashioned their own ecosystem. We were part of a natural process that altered the landscape. In that light, we can think of the domestic cat as an ecological response to the emergence of parasites (rodents attracted by early Neolithic granaries). The same forces that reshaped the genomes of our domesticates also reshaped ours.

一個更有幫助的解釋是，在過去的1萬年裏，人類塑造了自己的生態系統。我們是改造自然面貌的自然過程中的一部分。鑑於此，我們可以這樣看：在新石器時代早期，人類儲藏穀物的地方就招來了老鼠，而家貓的出現，則是生態系統對這些吃白食的齧齒動物做出的反應。重塑了家養動物基因組的力量，也重塑了我們自己的基因組。

No longer roving in small bands subsisting on game and unprocessed plants, we settled down in villages, harvesting the same crops year after year. For millenniums, peasants fed on what we might today term porridge, of various types. Our teeth became smaller — indeed, both dogs and humans show evidence of adaptation to starchy diets.

當我們不再組成小羣體四處遊蕩，不再依靠獵物和未經烹調的植物爲生，而是在村莊裏安定下來，年復一年地收穫着同樣的作物。數千年來，農民都在食用我們今天稱爲粥的各種飯食。於是我們的牙齒變小了——的確，狗和人類都表現出了適應澱粉類食物的跡象。

Just as the fur of our mammalian domesticates, freed from the constraint of needing to fade into the landscape, became a riot of diverse colors, human pigmentation started to change and many populations became light-skinned. With a cheek-by-jowl existence, humans and their animals began sharing diseases, remolding the immunity of whole populations, but leaving those who did not experience this co-evolution untouched and vulnerable. Possibly, some pathogens incubated in cats, like Toxoplasma gondii, may even alter human behavior.

經過人類馴化的哺乳動物的皮毛，在不需要適應環境的顏色後，變化成了各種各樣的顏色。與此相同，人類的色素沉着開始發生變化，許多人羣變成了淺膚色。在緊密共處的過程中，人類和他們的動物開始患同樣的疾病，從而重塑了整個種族的免疫系統，但那些未曾經歷這種共同進化歷程的種族，卻沒有受到影響，因而容易患病。弓形蟲等在貓體內孕育的病原體，甚至可能會改變人類行爲。

Many of us conceive of our relationship to our pets as analogous to that between a parent and child. But the natural history tells a more pragmatic tale. Cats emerged in the context of profound ecological changes to the post-ice-age landscape wrought by humans.

許多人都認爲，我們與寵物的關係就如同父母與孩子的關係。但是，自然史講述了一個更加實際的故事。在冰川時代過後的地貌上，人類造就了顯著的生態變化，貓就是在這種背景下出現的。

We were the authors of those changes, but in the process of telling that story, we became protagonists within it. One of the essential steps in knowing ourselves, and seeing where we are going, is to look around and take note of how we’ve reshaped those nearest to us, and they us.

我們是這些變化的作者，但在講述這個故事的時候，我們也成了它的主角。在瞭解我們自身、觀察我們將走向何方的過程中，一個關鍵步驟是環顧四周，研究我們怎樣重塑了離我們最近的那些生物，以及它們如何塑造了我們。