原文地址：大西洋月刊
原創翻譯：龍騰網 翻譯：飛雪似煬花
正文翻譯：
For decades, poultry breeders have transformed the genomes of turkeys, creating ever-larger birds.
幾十年來，家禽飼養者已經改變了火雞的基因組，創造了越來越大的鳥類。
A turkey today is not the turkey of yesteryear.
今天的火雞已經不是昔日的火雞。
For decades, animal breeders have been transforming the genomes of turkeys to make them grow larger. Since 1960, the weight of turkeys has gone up about a quarter of a pound each year. The average weight of a turkey has gone from 15.1 pounds in 1960 to 31.1 pounds in 2017.
幾十年來，動物飼養者一直在改變火雞的基因組，讓它們變得越來越大。自1960年以來，火雞的重量每年增加約四分之一磅，從而使這種鳥類的平均體重從1960年的15.1磅增加到2017年的31.1磅。
Average Turkey Weight 1960-2016
1960年至2016年期間土雞的平均體重
And most of that change has been genetic. In one study of a representative strain of turkeys, poultry researchers fed the same diet to turkeys from 2003 and to a control group of turkeys that were representative of that strain’s genetic pool from 1966. On average, the 2003 females grew to 33 pounds. Their 1966 cousins only got to 16.3 pounds.
大部分的變化都是具有遺傳性的。在一項對火雞的一種有代表性的類別的研究中，家禽研究人員從2003年開始給一組普通火雞和一組取自1966年的這一種類基因庫中具有代表性的受控火雞群體提供相同的飲食。平均而言，2003年的雌性火雞體重增加到了33磅，它們1966年的表親只有16.3磅。
The 2003 turkeys also grew much faster, reaching the same saleable weight twice as fast as their 1966 cousins. Even when they are raised under identical conditions, these are different animals with different genomes. Imagine if the average human were 300 pounds and reached what we now consider adult size at age 10, all while eating less food per pound of human. This is what just 60 years of scientific turkey breeding has wrought.
2003年的火雞的生長速度也更快，它們達到同樣的重量要比1966年的表親快了兩倍。即使它們在相同的條件下長大，它們也是不同的、有著不同基因組的動物。想像一下，如果普通人類的體重是300磅，如果人類在10歲時就達到了我們現在所認為的成年人的尺寸，那麼人類每磅重量所需要的食物攝入量就會減少。這就是60年的火雞科學繁育所帶來的成果。
「Farmers grow for what the consumer wants—and that includes meatier turkeys,」 said Keith Williams of the National Turkey Federation. 「The live weights of turkeys, due to that consumer desire, has continued to grow, and the amount of feed to raise each pound of turkey continues to be less.」
國家火雞聯盟的基思威廉斯說:「農民們想要的是消費者想要的東西，而這其中就包括了更大的火雞。基於消費者的需求，火雞的生活重量一直在增加，而每磅火雞所需要的飼料量則持續減少。」
Less feed reduces farmers』 costs, and it has environmental benefits, too, as less corn and soybeans are required to meet the nation’s turkey demand. And that demand has gone up a lot. In 1950, America’s per-capita turkey consumption was just 5.5 pounds. Nowadays, that number is over 16 pounds, and the National Turkey Federation would like to see it grow to 20 pounds, which would beat the industry’s peak consumption of 18.2 pounds of turkey per American in 1996.
減少飼料可以減少農民的成本，同時也能帶來環境效益，因為這樣滿足全國火雞需求的玉米和大豆數量就會減少。在1950年，美國人均消費的土雞重量僅為5.5磅。現在，這個數字已經超過了16磅，而國家火雞聯盟希望它能增長到20磅，這將超過1996年美國人均18.2磅的火雞消耗量。
Turkeys are no different from other livestock. Chickens have undergone a very similar process. Cows used to produce 5,000 pounds of milk. Now they produce more than 20,000 pounds. Selective-breeding programs combined with the development of quantitative genetics have combined to create systems for morphing our livestock to better fit the market.
火雞和其他家畜沒有什麼不同。雞也經歷了非常相似的過程。奶牛過去只能生產5000磅的牛奶。現在它們的產量超過了2萬磅。選擇性育種項目結合計量遺傳學的發展，共同創造出了使我們的牲畜和家禽變形以便更好地適應市場需求的系統。
For all these breeding programs, the key technology has been artificial insemination. A given male with the kinds of traits that breeders are looking for can be mated to many, many, many females. One bull, Pawnee Farm Arlinda Chief, had 2 million great-granddaughters, and is responsible for 14 percent of all the genetic material in Holstein cows.
在所有這些育種項目中，關鍵技術都是人工授精。一隻給定的具有繁殖能力的雄性動物個體可以與許多許多的雌性個體交配。一隻名為Pawnee Farm Arlinda Chief的種牛有200萬頭的曾孫女，它們佔據了荷斯坦奶牛所有遺傳物質的14%。
While these programs are analogous to humans』 original domestication of these animals, it is different enough in degree to become different in type. This is market-driven hyperdomestication.
雖然這些程序與人類最初馴化這些動物的方式類似，但在程度上是不同的，在類型上也有不同之處。這是市場驅動的「超級馴化」。
And there are trade-offs. While turkeys』 overall mortality rates do not seem to be higher than earlier generations, they—like our ever larger chickens—do suffer some new kinds of health problems. Their bodies can struggle to hold up their weight, leading to leg problems. And sometimes breeding exclusively for size can have a negative effect on animals』 fitness and fertility, which was an unintended side effect. Poultry scientists now say 「fitness traits must be measured and incorporated into selection objectives.」
當然也存在著利益權衡。雖然火雞的總體死亡率似乎沒有比前幾代高，但像我們現在所碰到的這樣的「大雞」，確實會出現一些新的健康問題。它們要努力保持體重，這導致了它們的腿部出現問題。而且，有時只以體型為標準進行繁育會對動物的健康和生育能力產生負面影響，這是一種意想不到的副作用。現在，家禽科學家們說:「必須衡量健康特徵，並納入到選擇目標當中。」
In turkeys, pure body-weight growth has been decelerating. In the 1980s, turkeys put on an average of 0.25 pounds per year. In the 1990s, that shot up to 0.41 pounds. In the 2000s, the number was down to 0.33. And this decade, we’re looking at 0.22 pounds per year so far.
就土雞而言，其單純的體重增長一直在減速。在20世紀80年代，火雞平均每年的體重增加量為0.25磅。在20世紀90年代，這一年均增長幅度達到了0.41磅。在本世紀頭十年，這個數字降到了0.3磅3。而在現在這十年裡，到目前為止，我們尋求的年均火雞體重增幅是0.22磅。
At some point, the growth of these birds will hit a market or a genetic limit, but it’s an open question which one they will reach first.
在某種程度上，這些鳥的生長必將會遇到一個市場層面或一個基因層面的極限，但會先觸及哪一種極限仍是一個問題。