地球上智慧物种只崛起过一次Intelligent Species Have Risen Only Once on Planet Earth
Brett： 嗯，那是一种说法，面对不确定性我们必须保持谦逊，因为没人知道答案。但我想提出一个几乎没什么人讨论的观点。
这个观点是：我们是孤独的。
这个观点与天文学无关，它完全关乎生物学。论证是这样的：看看地球，看看物种的数量——不仅包括现存于世的数百万种物种，还包括曾在地球上存在过的所有物种，那有数亿种。
生命大约在三十五亿年前出现，而在大约二十五亿年的时间里，除了细菌之外一无所有。所以生命显然没有多大动力去超越细菌快速进化；它只是尽可能地保持简单。
很多人都有这样一个错误观念，而达尔文恰恰已经驳倒了它——即进化有一个预设的方向。你会看到高中教科书里的那些进化图：一只猴子四肢着地蹒跚而行；然后它弓着身子；最后它直立起来，手里提着公文包，仿佛这就是进化预设的目标。这只是在事后回望时，看起来才像是进化预设的方向。
有一位美国学者查利·莱恩韦弗（Charley Lineweaver），他把这称为"人猿星球"假说——也就是说，如果你把人类从一颗星球上移除，猿类自然会进化来填补智力这个生态位。
他说你可以想象另一种情形：你是一头能够思考自己的大象。它们反思自己鼻子的长度，回望生物进化的历史，看到鼻子变得越来越短。于是它们得出结论："啊，进化一直以长出更长的鼻子为目标。这就是进化的全部意义所在。"
当然，我们能看出这很荒谬。只是碰巧这种叫做大象的生物进化出了长长的鼻子，但鼻子的长度似乎并不是进化的趋同特征。
趋同特征是这样一种特征：它存在于生物实体之中，一次又一次地独立出现。翅膀是我最喜欢的例子。鱼类有某种翅膀。有飞鱼。蝴蝶有翅膀，所以昆虫中也有。翅膀也出现在哺乳动物身上，比如狐蝠和某些种类的负鼠。当然，鸟类和恐龙也有翅膀。
在所有这类物种中，翅膀都独立地反复出现。眼睛也是如此，感知声音的器官也是如此。
现在让我们想想做数学的能力，或者建造射电望远镜的能力——换句话说，成为一个有智慧、有创造力的物种的能力。在地球的地质历史中，这种情况出现过几次？只出现在一个物种身上，而且只有这一个物种。
我们能据此得出结论说，智慧物种的出现是必然的吗？如果你把几颗细菌撒遍宇宙中所有适合生命存在的星球，重复这个实验，你能保证得到一个像我们这样的实体吗？
Brett: Now, that’s one argument, and we have to be humble in the face of uncertainty here because no one knows. But I want to give an argument that rarely gets any air time.
The argument is that we are alone.
The argument has nothing to do with astronomy; it has everything to do with biology. The argument goes like this: Look at planet Earth and look at the number of species not only that exist right now—millions of them—but also the number of species that have ever existed on planet Earth, which is hundreds of millions.
Life arose something like three and a half billion years ago, and for about two and a half billion years there was nothing but bacteria. So life apparently doesn’t have much impetus to evolve quickly beyond bacteria; it just remains as simple as possible.
A lot of people have this misconceived idea that Darwin really did away with—the idea that evolution has a direction in mind. You see these pictures of evolution that appear in high school textbooks of the monkey that’s hobbling around on all fours; then he’s hunched over; and then eventually he is standing up and holding a briefcase, as if this is what evolution had in mind. It only seems to be what evolution had in mind in retrospect, by looking backward.
There’s an American academic, Charley Lineweaver, who calls this the “Planet of the Apes” hypothesis—as in, if you remove the humans from a planet, the apes would naturally evolve to fill the intelligence niche.
He said you could imagine another situation where you’re an elephant that is able to think about themself. They reflect on the length of their trunk, and they look back through biological evolution and see that trunks get ever shorter. So what they conclude is, “Ah, evolution has been geared towards making ever-longer trunks. That’s what evolution is all about.”
Of course, we can see that that’s ridiculous. It just happens to be the case that this creature called the elephant has evolved and it’s got this long trunk, but the length of the trunk doesn’t appear to be a convergent feature of evolution.
A convergent feature of evolution is a feature that exists within biological entities that has arisen again and again, independently. Wings are my favorite example. Fish have wings of a certain kind. There are flying fish. Butterflies have wings, so we’ve got them in insects. They arose in mammals as well, with flying foxes and certain kinds of possums. And, of course, birds and dinosaurs had wings as well.
Independently, in all these species, the wings keep arising. So do eyes, and so do organs for sound.
Now let’s think about the capacity to do mathematics or to build radio telescopes—in other words, to be an intelligent, creative species. How many times has that arisen in the geological history of the Earth? In one species and one species alone.
Can we conclude on that basis that, therefore, it’s inevitable that intelligent species will arise? If you were to repeat the experiment by sprinkling a few bacteria around all the bio-friendly planets that exist throughout the universe, would you be guaranteed to get an entity like us?