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Narrator:Listen to part of a lecture in a zoology class.
獨白:聽下面一段動物學課堂的講解。
Professor:A mass extinction as when numerous species become extinct over a very short time period, short,
教授:大量消亡是指大規模的物種在短期內滅絕的現象，這里的短期，
geologically speaking that is, like when the dinosaurs died out 65 million years ago.
從地質學角度來講就是像六千五百萬年前恐龍滅絕一樣。
And the fossil record, it indicates that in all the time that animals have inhabited Earth, there have been five great mass extinctions,
而且化石記錄顯示，地球上生存過的物種已經經歷過五次的大量消亡，
dinosaurs being the most recent.
恐龍滅絕是最近的一次。
In each of the others up to half of all land animals and up to 95 percent of marine species disappeared.
每次物種滅絕，都有半數甚至 95%的海洋生物徹底消失。
Well, today we are witnessing a sixth mass extinction,
那么今天我們正在目睹著第六次大量消亡，
but unlike the others, the current loss of bio-diversity can be traced to human to human activity.
和前幾次不一樣，這次生物多樣性的消失是由人類活動導致的。
Since the Stone Age, humans have been eliminating species and altering ecosystems with astounding speed.
從石器時期開始，人類就在以驚人的速度消除物種，并改變著生態系統。
Countless species have disappeared due to over-hunting,
不計其數的物種的消失都由于人類的過度捕獵、
habitat destruction and habitat fragmentation,pollution and other unnatural human causes.
棲息處摧毀及破壞、污染及其他人類引起的非自然原因引起的。
So, as a way of repairing some of that damage, a group of conservation biologists has proposed an ambitious, or some might say,
因此，作為對這些破壞的修復，一群保護主義生物學家提出了一個雄心勃勃的計劃，有人可能會覺得這個計劃很激進。
a radical plan, involving large vertebrates, or , megafauna.
這個計劃涉及到了大型脊椎動物或巨型動物。
Megafauna include elephants, wild horses, big cats, camels, large animals.
巨型動物包括大象、野馬、大型貓科動物、駱駝等。
Eh, actually, the proposal focuses on a particular subset of megafauna, the kind that lived during the Pleistocene epoch.
呃，其實，這項提議主要是針對一個居住于更新世的巨型動物支群。
Ok. The Pleistocene epoch, most commonly known as the Ice Age, stretched from 1.8 million to 11,500 years ago.
好的。更新世，也就是大家熟知的冰河時代，從一百八十萬年前延伸至一萬一千五百年前。
In the Americas, many megafauna began disappearing by the end of the Pleistocene.
在美洲，很多巨型動物在更新世后期開始消失。
So here's the biologists' idea.
那么生物學家們的想法是這樣的。
Take a select group of animals, megafauna from places like Africa and Asia, and introduce them into other ecosystems similar to their current homes, beginning in the United States.
從非洲及亞洲選一批動物，然后把它們引進到與它們目前生活環境相似的生態系統中，從美國開始。
They call their plan Pleistocene rewilding.
他們稱之為更新世野生動物重返計劃。
Now, the advocates of Pleistocene rewilding cite two main goals.
現在，更新世野生動物重返的提倡者們主要是有兩大目標。
One is to help prevent the extinction of some endangered megafauna by providing new refuges, new habitats for them.
一個是通過提供新的避難所和棲息地幫助防止瀕臨滅絕的巨型動物繼續消亡，
The other is to restore some of the evolutionary and ecological potential that has been lost in North America.
另一個是重建北美已喪失的一些進化及生態的潛能。
What do I mean by restore evolutionary potential?
重建進化及生態的潛能是什么意思呢？
Well as you know the evolution of any species is largely influenced by its interactions with other species.
你們都知道，物種的進化很大程度上受與其相互活動的物種的影響。
So during the Pleistocene epoch… let's take the now extinct American cheetah, for instance.
所以在更新世時期，我們來拿已經絕種的美洲印度豹來舉例。
We believe it played a pivotal role in the evolution of the pronghorn antelope, the antelope's amazing speed,
我們相信它在叉角羚的進化中起重要的作用，
to be exact, because natural selection would favor those antelope that could outrun a cheetah.
精確來講，羚羊驚人的速度是一種自然選擇的結果，因為只有能跑過印度豹的羚羊才能生存下來。
When the American cheetahs disappeared, their influence on the evolution of pronghorn and presumably on other prey animals stopped.
當美洲印度豹絕種以后，它們對叉角羚及其他可能獵食的動物進化的影響就停止了。
So it is conceivable that the pronghorn antelope would have continued to evolve, get faster maybe, if the cheetahs were still around.
所以可以想象，如果印度豹還存在的話，叉角羚本可以繼續進化，跑的更快。
That's what's meant by evolutionary potential.
這就是進化潛能。
Importing African cheetahs to the western United States could,
按照這些生物學家的說法，從非洲向美國引進印度豹，
in theory, put the pronghorn back onto its…uh, natural evolutionary trajectory according to these biologists.
在理論上就可以將叉角羚放回在其自然那的進化軌跡上來。
Another example is the interaction of megafauna with local flora, in particular, plants that rely on animals to disperse their seeds.
另一個例子就是巨型動物和本地植物群的相互聯系，尤其是那些僅依賴動物傳播種子的植物。
Like Pleistocene rewilding could spark the re-emergence of large seeded American plants, such as the maclura tree.
更新世野生動物重返可以促使美國一些種子顆粒大的植物重新出現，比如桑橙樹。
Many types of maclura used to grow in North American,
以前在美國北部有很多種類型的桑橙樹，
but today, just one variety remains and it is found in only two states.
而現在，只剩下了一種，而且僅在生長在兩個州。
In the distant past, large herbivores like mastodons dispersed maclura seeds, each the size of an orange in their droppings.
在不遠的過去，大型的食草動物比如說乳齒象就傳播桑橙樹種子，橙子般大小的種子從它們的口中露出，便能得到傳播。
Well, there aren't any mastodons left, but there are elephants, which descended from mastodons.
而現在已經沒有乳齒象了，但是有大象，也就是乳齒象的后代。
Introduce elephants into that ecosystem and they might disperse those large maclura seeds, like their ancestors did. Get the idea?
將大象引進到這個生態系統中可能就會幫助傳播大顆粒種子了，正如它們的祖先一樣。明白了嗎？
Restoring some of the former balance to the ecosystem?
重建一些曾經的生態平衡？
But as I alluded to earlier, Pleistocene rewilding is extremely controversial.
但是正如我之前暗指的一樣，更新世野生動物重返非常的富有爭議性。
A big worry is that these transplanted megafauna might devastate plants and animals that are native to the western United States.
最讓人憂心的就是這些轉移過來的巨型動物可能會毀滅美國西部一些土生土長的動植物。
In the years since the Pleistocene epoch, native species have adapted to the changing environmental there, plants, smaller animals, they have been evolving without megafauna for millennia.
自從更新世之后，本地的物種就一直在適應那里變化著的環境，植物、小動物在這個千年期內都是在沒有巨型動物的環境下進化的。
Also, animal species that went extinct 11,000 years ago, uh, some are quite different genetically from their modern-day counterparts,
同樣，這些一萬一千年前就絕種的動物，和今天與其相似類的動物們基因有很大差異，
like elephants don't have thick coasts like their mastodon ancestors do when they graze the prairies of the America West during the Ice Age.
比如大象的祖先乳齒象有一層厚厚的皮，它們層在冰河時期的美國西部草原上吃草，而大象則沒有。
Granted, the climate today is not as cold as it was in the Pleistocene.
但是，今天的氣候也不像更新世那時候那么冷。
But winters on the prairie can still get pretty harsh today.
而草原上的冬天現在依舊是很嚴寒。
And there are many more considerations.
而且還有眾多需要考慮到的因素。
Well, you see how complex this is.
你們應該可以看到這個復雜性。
If you think about it though, the core problem with this sixth mass extinction is human interference.
如果你仔細的想一下，其實第六次大量消亡的核心問題是人類的干預。
Pleistocene rewilding is based on good intentions,
更新世野生動物重返計劃意圖是好的，
but you know, it probably would just be more of the same thing.
但是你們知道，這很可能會使情況更加惡化。
