淺談爲什麼狗不能活得像人類一樣長?
Dogs are mammals like humans, and they have a heart, lungs and all the things you need to survive.
狗是像人類一樣的哺乳動物，它們擁有心臟、肺和所有生存所需的東西。Our pet dogs give us so much happiness, but then so much sadness when they die. So why don't they survive as long as us?
我們的寵物狗給了我們如此多的快樂，但是當他們死去時，我們是那麼的悲傷。那麼爲什麼他們不能活得像我們一樣久呢？Scientists worked out a long time ago that the lifespan of animals is mostly related to their size. Bigger animals usually live longer than smaller animals.
很久以前，科學家就研究出動物的壽命與它們的體型大小有關。較大的動物通常比較小的動物壽命更長。
The main reason people used to think big animals live longer is because of something called metabolic rates.
人們過去認爲大動物活得更長的主要原因是因爲代謝率。A metabolic rate is like how much petrol a car uses -- cars that use up their petrol more slowly can drive for longer, a bit like animals with lower metabolic rates.
代謝率就像一輛汽車使用多少汽油，更慢地使用汽油的汽車可以開得更久，有點像代謝率較低的動物。Smaller animals usually have higher metabolic rates, which lead to shorter lifespans, like a car that uses up its petrol very quickly.
較小的動物通常具有較高的新陳代謝率，這導致壽命縮短，就像汽車很快耗盡汽油一樣。
The problem is that this doesn't work for all animals. Some parrots have high metabolic rates but can live for more than 80 years! A metabolic rate is related to heart rate, and some parrots have a heart rate of 600 beats per minute. (Your heart beats around 70 to 100 times per minute.)
問題是這並不是對所有的動物都起作用。一些鸚鵡的代謝率很高，但可以活80年以上！代謝率與心率有關，一些鸚鵡的心率爲每分鐘600次。（你的心臟每分鐘跳動70到100次左右。）And dogs are one of the animals that do not follow this rule. A 70kg Great Dane is lucky to reach seven years, but a 4kg Chihuahua can live for 10 years or more.
而狗是不遵循這個規則的動物之一。一隻70公斤的大丹犬，如果幸運，壽命能達到7年，但是4公斤的奇瓦瓦狗可以活10年或更長時間。We still don't really know why this happens. But if you want a dog that lives longer, you should choose a small breed.
我們仍然不知道爲什麼會發生這種情況。但是如果你想要一隻活得更長的狗，你應該選擇一個小品種。People now think it might depend on the "evolutionary pressures" that each animal faces. An evolutionary pressure includes things like other animals that want to kill you for food.
人們現在認爲這可能取決於每隻動物所面臨的“進化壓力”。進化壓力包括其他想要獵殺你的動物。Because they are so big, large animals like elephants and whales are less likely to be attacked in the wild than small animals like guppies or mice.
因爲非常大，所以像大象和鯨魚這樣的大型動物，不會像野生動物或老鼠這樣的小動物在野外那麼容易受到攻擊。
