What is so special about the human brain? | Suzana Herculano-Houzel

翻译人员: Dasheng Chen 校对人员: Zhiting Chen

What is so special about the human brain?

对于人类的大脑来说，什么是最特别的？

Why is it that we study other animals

我们为什么要研究其他的动物？

instead of them studying us?

而不是他们研究我们？

What does a human brain have or do

有没有什么是人类大脑可以做的

that no other brain does?

而其他的大脑不能做的？

When I became interested in these questions about 10 years ago,

十年前，我对这些问题产生兴趣

scientists thought they knew what different brains were made of.

科学家认为他们知道大脑不同的组成部分

Though it was based on very little evidence,

即使那些都是基于一些非常小的证据，

many scientists thought that all mammalian brains,

很多科学界认为所有的哺乳动物的大脑，

including the human brain,

包括人类的大脑

were made in the same way,

是由同样的东西组成，

with a number of neurons that was always

一系列的神经元和大脑的大小

proportional to the size of the brain.

总是成为成正比

This means that two brains of the same size,

这个以为着，两个同样大小的大脑

like these two, with a respectable 400 grams,

就看这两个，有大概400克，

should have similar numbers of neurons.

应该有同样数量的神经元

Now, if neurons are the functional

如果我们说神经元是大脑

information processing units of the brain,

功能信息处理的单位

then the owners of these two brains

然后，这些两个大脑各自的拥有者

should have similar cognitive abilities.

应该有的相近的认知能力。

And yet, one is a chimp,

然而，其中一个是黑猩猩，

and the other is a cow.

和另一种是一头母牛。

Now maybe cows have a really rich

现在也许牛有很丰富的

internal mental life and are so smart

精神生活，并且很聪明

that they choose not to let us realize it,

他们选择不会让我们意识到这一点，

but we eat them.

但我们吃他们。

I think most people will agree

我想大多数人会同意

that chimps are capable of much more complex,

相比于牛来说，黑猩猩具有更加复杂

elaborate and flexible behaviors than cows are.

和细节，以及灵活的行为。

So this is a first indication that the

所以这是第一个征兆显示

"all brains are made the same way" scenario

"所有的大脑的构成方式都是一样的"

is not quite right.

不是特别正确的。

But let's play along.

我们不妨继续这个比喻

If all brains were made the same way

如果所有的大脑由相同的方式组成

and you were to compare animals with brains of different sizes,

你要将大脑大小不同的动物拿来做比较,

larger brains should always have more neurons

大一点的大脑对于小一点的大脑来说

than smaller brains, and the larger the brain,

应该具有等多的神经元， 并且越大的大脑，

the more cognitively able its owner should be.

它的主人应该更有认知能力。

So the largest brain around should also be

所以最大的脑应该具有

the most cognitively able.

最好的认知能力。

And here comes the bad news:

这里有个坏消息要说：

Our brain, not the largest one around.

我们的大脑，不是最大的一个。

It seems quite vexing.

看起来相当棘手。

Our brain weighs between 1.2 and 1.5 kilos,

我们的大脑重量 1.2 和 1.5 公斤之间

but elephant brains weigh between four and five kilos,

但大象脑子称之间四、 五公斤

and whale brains can weigh up to nine kilos,

鲸鱼大脑可重达 9 公斤

which is why scientists used to resort to saying

这就是为什么科学家们用来诉诸说

that our brain must be special

我们的大脑肯定是非常特别地

to explain our cognitive abilities.

来解释我们的认知能力。

It must be really extraordinary,

它必须是真的非同寻常，

an exception to the rule.

一个例外情况。

Theirs may be bigger, but ours is better,

他们的大脑可能会更大，但我们的更好，

and it could be better, for example,

并且我们的可以变得更加好，例如，

in that it seems larger than it should be,

在这似乎比它应该更大

with a much larger cerebral cortex than we should have

与很多大大脑皮层比我们应该有的

for the size of our bodies.

对于我们的身体的大小。

So that would give us extra cortex

因此，这样将会给我们额外皮质

to do more interesting things than just operating the body.

去做更多有趣的事情，而不是只主管我的身体。

That's because the size of the brain

这是因为大脑的大小

usually follows the size of the body.

通常遵循身体的大小。

So the main reason for saying that

所以说这句话的主要原因就是

our brain is larger than it should be

我们的大脑已经比它应有的大小大出好多了

actually comes from comparing ourselves

其实是来自于比较我们自己

to great apes.

和巨猿。

Gorillas can be two to three times larger than we are,

大猩猩可以是比我们大两到三倍

so their brains should also be larger than ours,

因此，他们的大脑也应该比我们的大

but instead it's the other way around.

但相反，它的大脑比我们的小。

Our brain is three times larger than a gorilla brain.

我们的大脑是比大猩猩脑大三倍。

The human brain also seems special

人类的大脑似乎也很特别

in the amount of energy that it uses.

在于它使用的能源的量。

Although it weighs only two percent of the body,

虽然它的重量只有全身的2%，

it alone uses 25 percent of all the energy

但是它单独使用

that your body requires to run per day.

你身体每天所需能量的25%

That's 500 calories out of a total of 2,000 calories,

2000卡路里里面的500卡路里

just to keep your brain working.

仅仅只是为了让你的大脑的工作。

So the human brain is larger than it should be,

所以，人类的大脑已经比应有的大小大出很多了

it uses much more energy than it should,

它消耗了更加多的能量，对于他应该消耗的来说

so it's special.

所以它很特殊。

And this is where the story started to bother me.

这是这个故事开始让我感到疑惑。

In biology, we look for rules

在生物学中，我们发现规则

that apply to all animals and to life in general,

一般情况下，适用于所有的动物和生活

so why should the rules of evolution

那么为什么进化的规则

apply to everybody else but not to us?

应用到了其他生物，但不是我们？

Maybe the problem was with the basic assumption

也许这个问题是一个基础的假设

that all brains are made in the same way.

所有的大脑都是由相同的方式组成。

Maybe two brains of a similar size

也许两个大小相似的大脑

can actually be made of very different numbers of neurons.

实际上可以由数目不同的神经元组成。

Maybe a very large brain

也许是一个非常大的大脑

does not necessarily have more neurons

不一定需要具有更多的神经元

than a more modest-sized brain.

对于一个更具规模适度的大脑。

Maybe the human brain actually has the most neurons

也许，相比于其他大脑来说，人类的大脑具有

of any brain, regardless of its size,

最多的神经元，无论其规模大小，

especially in the cerebral cortex.

尤其是在大脑皮质中。

So this to me became

所以这对我来说成为了

the important question to answer:

对于这个答案来说最重要的问题

how many neurons does the human brain have,

人类大脑有多少神经元

and how does that compare to other animals?

和其他动物比较起来怎样？

Now, you may have heard or read somewhere

现在，您可能会听到或读到过

that we have 100 billion neurons,

我们有 1000 亿个神经元

so 10 years ago, I asked my colleagues

10 年前，我就问我的同事们

if they knew where this number came from.

他们是否知道这个数字是从哪里来的。

But nobody did.

但没人知道。

I've been digging through the literature

我通过深入细致的研究文献

for the original reference for that number,

试图找出该数字的原始参考

and I could never find it.

但我找不到它。

It seems that nobody had actually ever counted

这似乎其实没有人去真正的数过

the number of neurons in the human brain,

人类大脑里面的神经元数量，

or in any other brain for that matter.

或者其他任何的大脑里面神经元的数量。

So I came up with my own way to count cells in the brain,

所以我想出了我自己的方式来统计大脑里面的细胞，

and it essentially consists of

它最重要的一个步骤是

dissolving that brain into soup.

那大脑溶解在试剂里。

It works like this:

它的工作方式：

You take a brain, or parts of that brain,

你带一个大脑或部分的大脑，

and you dissolve it in detergent,

让它溶化在洗涤剂里，

which destroys the cell membranes

洗涤剂会破坏细胞膜

but keeps the cell nuclei intact,

但保持细胞核不变，

so you end up with a suspension of free nuclei

所以你最终会看到细胞核悬浮

that looks like this,

看起来像这样，

like a clear soup.

像一碗清汤。

This soup contains all the nuclei

这汤包含所有细胞核

that once were a mouse brain.

曾经是一个老鼠的大脑。

Now, the beauty of a soup is that because it is soup,

现在，这个液体的魅力在于因为它是液体，

you can agitate it and make those nuclei

可以摇晃它，并使这些细胞核

be distributed homogeneously in the liquid,

在液体中均匀分布

so that now by looking under the microscope

所以，现在通过在显微镜下观察

at just four or five samples of this homogeneous solution,

只需四个或五个 这种细胞核均匀分布的样本

you can count nuclei, and therefore tell

你可以数数原子核，并能够知道

how many cells that brain had.

有多少脑细胞了。

It's simple, it's straightforward,

这样很简单，非常直接，

and it's really fast.

并且，这样的速度也很快。

So we've used that method to count neurons

所以我们使用了这种方法来计数神经元

in dozens of different species so far,

目前为止计数了几十个不同的物种，

and it turns out that all brains

结果发现，所有的大脑

are not made the same way.

是由不同的方式组成的。

Take rodents and primates, for instance:

以啮齿类动物和灵长类动物为例：

In larger rodent brains, the average size

在大一些的啮齿类动物大脑里，

of the neuron increases,

神经元的平均尺寸在增加，

so the brain inflates very rapidly

所以，大脑非常迅速地膨胀

and gains size much faster than it gains neurons.

尺寸增长比获得神经元更加快

But primate brains gain neurons

但灵长类动物的大脑得到神经元

without the average neuron becoming any larger,

而不需要神经元平均尺寸增大

which is a very economical way

这是一种非常经济的方法

to add neurons to your brain.

在你大脑里添加神经元

The result is that a primate brain

结果是灵长类动物的大脑

will always have more neurons than a rodent brain of the same size,

和啮齿动物相同大小的脑相比, 总有更多的神经元

and the larger the brain,

和大脑越大

the larger this difference will be.

这种差异性將越來越大

Well, what about our brain then?

那么,我们的大脑又是如何呢?

We found that we have, on average,

我们发现我们平均有

86 billion neurons,

860 亿个神经元

16 billion of which are in the cerebral cortex,

其中有 160 亿个存在于大脑皮质里

and if you consider that the cerebral cortex

而且如果你认为大脑皮质

is the seat of functions like

是下列功能的基础，

awareness and logical and abstract reasoning,

意识,逻辑和抽象推理，

and that 16 billion is the most neurons

那么，这160 亿个神经元

that any cortex has,

对大脑皮质来说是最重要的

I think this is the simplest explanation

我想这是最简单的說明

for our remarkable cognitive abilities.

对于我们卓越的认知能力。

But just as important is what the 86 billion neurons mean.

但,就和 860 亿神经元的意义一样重要

Because we found that the relationship

因为我们发现了

between the size of the brain and its number of neurons

大脑的大小和其神经元数目之间的关联

could be described mathematically,

是可以用数学模型来计算的

we could calculate what a human brain

我们可以计算出人类大脑

would look like if it was made like a rodent brain.

如果被作成像是一个啮齿类动物的大脑会如何。

So, a rodent brain with 86 billion neurons

所以，有着 860 亿神经元的啮齿类动物大脑

would weigh 36 kilos.

将重 36 公斤。

That's not possible.

那是不可能的。

A brain that huge would be crushed

巨大的大脑將会被

by its own weight,

它自己本身的重量所挤压，

and this impossible brain would go

这个不可能的大脑將会适用于

in the body of 89 tons.

一个89吨的身体 。

I don't think it looks like us.

我不认为它看起来跟我们一样。

So this brings us to a very important conclusion already,

因此，这已经带給我们的一个非常重要的结论，

which is that we are not rodents.

我们不是啮齿类动物。

The human brain is not a large rat brain.

人类的大脑不是一个大老鼠的大脑。

Compared to a rat, we might seem special, yes,

和一只老鼠相比，我们看起来可能特别些，是的

but that's not a fair comparison to make,

但这样的比较不公平，

given that we know that we are not rodents.

我们知道我们不是啮齿类动物。

We are primates,

我们是灵长类动物，

so the correct comparison is to other primates.

因此和其他的灵长类动物做正确的比较。

And there, if you do the math,

這里还有，如果你自己来算一下，

you find that a generic primate

你会发现一般的的灵长类动物

with 86 billion neurons

有着860 亿神经元

would have a brain of about 1.2 kilos,

将会有一个约 1.2 公斤的大脑

which seems just right,

这似乎刚刚好，

in a body of some 66 kilos,

在大约66 公斤身体中，

which in my case is exactly right,

在我的研究是完全正确的

which brings us to a very unsurprising

我们对此一点儿也不惊讶

but still incredibly important conclusion:

但这仍是令人难以置信的重要结论：

I am a primate.

我是灵长类动物。

And all of you are primates.

而且,你们全部都是灵长类动物。

And so was Darwin.

达尔文也是。

I love to think that Darwin would have really appreciated this.

我认为达尔文会很欣赏这个研究结论。

His brain, like ours,

他的大脑，像我们一样，

was made in the image of other primate brains.

和其它灵长类动物的大脑一样。

So the human brain may be remarkable, yes,

所以，人类的大脑可能是显著的,是的

but it is not special in its number of neurons.

但它特别之处不在于其神经元的数目。

It is just a large primate brain.

它只是一个大的灵长类动物的大脑。

I think that's a very humbling and sobering thought

我想这是个非常谦卑和发人深省的思考

that should remind us of our place in nature.

提醒了我们在自然界的位置。

Why does it cost so much energy, then?

为什么我们的大脑消耗这么大的能量，然后呢？

Well, other people have figured out

有些人已经想通了，

how much energy the human brain

人类的大脑能消耗多少能量

and that of other species costs,

和其他物种的大脑消耗多少能量

and now that we knew how many neurons

而现在,我们知道

each brain was made of, we could do the math.

每个大脑中有多少神经元，我们可以算一算。

And it turns out that both human

结果是,人类

and other brains cost about the same,

和其他物种的大脑消耗相同的能量

an average of six calories per billion neurons per day.

平均每日，每十亿个神经元消耗六个卡路里的热量。

So the total energetic cost of a brain

所以一个大脑全部精力的消耗

is a simple, linear function

是简单的，线性函数

of its number of neurons,

可计算其神经元的数目

and it turns out that the human brain

结果发现，人类的大脑

costs just as much energy as you would expect.

消耗的能量就跟你预期的一样

So the reason why the human brain

所以，为什么人类的大脑

costs so much energy is simply because

消耗如此多的能量的原因容易理解，

it has a huge number of neurons,

因为它有大量的神经元，

and because we are primates

还有,因为我们是灵长类动物

with many more neurons for a given body size

在一个特定大小的身体里,

than any other animal,

人类比任何其他的动物，有着更多的神经元

the relative cost of our brain is large,

我们的大脑的相对消耗量是很大的，

but just because we're primates, not because we're special.

但只是因为我们是灵长类动物，不是因为我们是特別的。

Last question, then:

最后一个问题，

how did we come by this remarkable number of neurons,

我们为什么有数量巨大的神经元，

and in particular, if great apes

特别是，如果巨猿

are larger than we are,

比我们更大，

why don't they have a larger brain than we do, with more neurons?

那为什么他们沒有一个有着更多神经细胞,比我们还大的大脑呢?

When we realized how much expensive it is

当我们意识到这个有多珍貴,

to have a lot of neurons in the brain, I figured,

在大脑中有大量的神经元，我想，

maybe there's a simple reason.

可能有一个简单的原因。

They just can't afford the energy

他们只是不能负担

for both a large body and a large number of neurons.

一个大型的身体以及多量的神经细胞共存所需的能量。

So we did the math.

所以我们算过

We calculated on the one hand

一方面，我们计算着

how much energy a primate gets per day

一个灵长类动物每一天获取多少能量

from eating raw foods,

借由吃生的食物，

and on the other hand, how much energy

另一方面，有多少能量

a body of a certain size costs

在一个特定大小的身体中消耗

and how much energy a brain of a certain number of neurons costs,

和有多少能量在含有特定数量神经元的大脑中消耗

and we looked for the combinations

然后我们找到一个结合

of body size and number of brain neurons

身体尺寸和大脑神经元数目

that a primate could afford

灵长类动物能夠负担得起

if it ate a certain number of hours per day.

如果它每天花一定数量的时间在吃上面。

And what we found is that

然后, 我们发现到

because neurons are so expensive,

因为神经细胞太珍貴了，

there is a tradeoff between body size and number of neurons.

有一个权衡出先在身体大小和神经元的數量之间。

So a primate that eats eight hours per day

所以, 一个灵长类动物每天吃八个小时

can afford at most 53 billion neurons,

能够负担最多 530 亿神经元，

but then its body cannot be any bigger

但是，它的身体不能

than 25 kilos.

超过25 公斤。

To weigh any more than that,

任何比这更重的重量

it has to give up neurons.

它必须放弃一些神经细胞。

So it's either a large body

所以,它不是一个庞大身体

or a large number of neurons.

就是一个大数量的神经元。

When you eat like a primate,

当你吃的像灵长类动物时，

you can't afford both.

你不能负担任何一方。

One way out of this metabolic limitation

一个方法超出此种代谢限制是

would be to spend even more hours per day eating,

每一天花更多的时间在吃饭上面，

but that gets dangerous,

但是，这样是很危险的

and past a certain point, it's just not possible.

某种程度上，它是不可能发生的。

Gorillas and orangutans, for instance,

大猩猩和红毛猩猩，例如，

afford about 30 billion neurons

能夠负担约 300 亿个神经元

by spending eight and a half hours per day eating,

它们每天花八个半小时吃饭，

and that seems to be about as much as they can do.

这似乎是它们所能做的一切。

Nine hours of feeding per day

9 个小时的每日饲喂

seems to be the practical limit for a primate.

是灵长类动物的实际限制。

What about us?

那我们呢?

With our 86 billion neurons

根据我们的860 亿神经元

and 60 to 70 kilos of body mass,

和 60 到 70 公斤的体重，

we should have to spend over nine hours

我们应该要花超过九个小时

per day every single day feeding,

每天在吃饭上

which is just not feasible.

这是不可行的。

If we ate like a primate,

如果我们像灵长类动物一样吃，

we should not be here.

我们不应该在这里。

How did we get here, then?

我们怎么在这里呢？

Well, if our brain costs just as much energy

好吧，如果我们的大脑消耗的能量跟他

as it should, and if we can't spend

应该所消耗的一致，并且如果我们不能把每天

every waking hour of the day feeding,

醒着的时间都花在吃饭上，

then the only alternative, really,

然后这个唯一的选择，真的，

is to somehow get more energy

是以某种方式

out of the same foods.

从相同的食品上获取更多的能量。

And remarkably, that matches exactly

引人注目的是，这和我们的祖先

what our ancestors are believed to have invented

早已发现的完全匹配

one and a half million years ago,

在一百五十万年前，

when they invented cooking.

他们发明了烹饪。

To cook is to use fire

要做饭就得使用火

to pre-digest foods outside of your body.

在食物进入你身体前预先消化食物。

Cooked foods are softer, so they're easier to chew

煮熟的食物比较软，所以他们更容易嚼烂

and to turn completely into mush in your mouth,

在你的嘴里完全粉碎

so that allows them to be completely digested

这就使他们能够完全被消化

and absorbed in your gut,

并且被你的肠道所吸收，

which makes them yield much more energy in much less time.

这使得它们在更少的时间内带来更多能源。

So cooking frees time for us to do

所以烹饪让我们有更多的时间，

much more interesting things with our day

去用我们的神经元

and with our neurons

做更多有趣的事情

than just thinking about food,

而不是只想着食物，

looking for food, and gobbling down food

寻找食物，并吞噬下食物

all day long.

花去整整一天。

So because of cooking, what once was

所以由于烹饪，曾是

a major liability, this large,

一个沉重的负担，这个大，

dangerously expensive brain with a lot of neurons,

且极其昂贵的，有着一大堆神经元的大脑，

could now become a major asset,

现在能够成为一项重要资产，

now that we could both afford the energy for a lot of neurons

现在，我们可以为给予神经元提供能量

and the time to do interesting things with them.

并且把时间用在去做一些有趣的事情。

So I think this explains why the human brain

因此，我认为这就解释了为什么人类的大脑

grew to become so large so fast in evolution,

在进化过程中增长如此之快，

all of the while remaining just a primate brain.

当所有剩余的只是一个灵长类动物的大脑。

With this large brain now affordable by cooking,

与这么大的大脑现在可以负担地起烹饪，

we went rapidly from raw foods to culture,

我们去迅速地进步着，从生食到文化，

agriculture, civilization, grocery stores,

农业、 文明、 杂货店、

electricity, refrigerators,

电力、 冰箱、

all of those things that nowadays

所有这些事物，现今

allow us to get all the energy we need

使我们能够得到我们需要的所有能量

for the whole day in a single sitting

一整天所需的所有能量

at your favorite fast food joint.

来自于你最喜欢的快餐食品。

So what once was a solution

所以曾是一种解决办法

now became the problem,

现在成为了这一问题，

and ironically, we look for the solution in raw food.

讽刺的是，我们在生食中寻找解决方案。

So what is the human advantage?

那么人类的优势是什么？

What is it that we have

我们有什么东西

that no other animal has?

是其他动物没有的吗？

My answer is that we have the largest number

我的答案是我们有最大数量

of neurons in the cerebral cortex,

神经元存在于大脑皮层中，

and I think that's the simplest explanation

并且我认为这能最简单地解释

for our remarkable cognitive abilities.

为什么我们有卓越的认知能力。

And what is it that we do that no other animal does,

还有就是我们做了什么是没有其他动物做的，

and which I believe was fundamental

我认为

to allow us to reach that large,

使我们能够达到这么多的，

largest number of neurons in the cortex?

最多数量的神经元存在于大脑皮质中的基本原因是

In two words, we cook.

两个词，我们做饭。

No other animal cooks its food. Only humans do.

没有其他动物烹饪它们的食物。只有人类才做。

And I think that's how we got to become human.

而且我认为，这就是我们是怎么成为人类的。

Studying the human brain changed the way I think about food.

研究人类大脑改变我对食物的想法。

I now look at my kitchen,

现在我看看自己的厨房，

and I bow to it,

然后我向它鞠躬，

and I thank my ancestors for coming up

然后我谢谢我的祖先想到

with the invention that probably made us humans.

这个有可能使我们成为人类的发明。

Thank you very much.

谢谢。

(Applause)

（掌声）