TEDGlobal 2013
Suzana Herculano-Houzel: What is so special about the human brain?
蘇珊納· 賀古拉奴 · 霍札 (Suzana Herculano-Houzel): 人腦有何特別之處?
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人腦令人感到困惑——對照我們的身體，它大的古怪，十分耗能量，大腦皮質密度又異常地高。這是怎麼回事呢？神經學家蘇珊納 賀古拉奴·霍札 (Suzana Herculano-Houzel) 戴上她的偵探帽，帶領我們解開這個謎題。經由製作「腦湯」，她下了一個驚人的結論。
Suzana Herculano-Houzel - Neuroscientist
Suzana Herculano-Houzel shrunk the human brain by 14 billion neurons -- by developing a new way to count them. Full bio
Suzana Herculano-Houzel shrunk the human brain by 14 billion neurons -- by developing a new way to count them. Full bio
Double-click the English transcript below to play the video.
00:12
What is so special about the human brain?
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人類的腦有什麼特別的呢？
00:15
Why is it that we study other animals
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為何是我們研究其它動物的腦
00:17
instead of them studying us?
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而不是我們的被研究呢？
00:19
What does a human brain have or do
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人腦擁有什麼
00:21
that no other brain does?
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其它動物的腦沒有的呢？
00:23
When I became interested
in these questions about 10 years ago,
in these questions about 10 years ago,
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十幾年前我開始
對這類的問題感興趣
對這類的問題感興趣
00:26
scientists thought they knew
what different brains were made of.
what different brains were made of.
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那時的科學家自認已知差異所在
00:28
Though it was based on very little evidence,
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即便可依據的證據非常少
00:30
many scientists thought that all mammalian brains,
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許多科學家認為所有哺乳類的腦
00:32
including the human brain,
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包括人類的頭腦
00:34
were made in the same way,
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都有著相同的構造
00:35
with a number of neurons that was always
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有著一定數量的神經元
00:37
proportional to the size of the brain.
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而數量與腦的大小成正比例
00:39
This means that two brains of the same size,
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這表示同樣大小的兩個腦
00:41
like these two, with a respectable 400 grams,
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例如這兩約400公克的
00:45
should have similar numbers of neurons.
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應有差不多數量的神經元
00:47
Now, if neurons are the functional
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如果神經元是腦裡面
00:49
information processing units of the brain,
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訊息處理的最小單位
00:52
then the owners of these two brains
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那這兩腦的主人
00:54
should have similar cognitive abilities.
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應該有著差不多一樣的認知能力
00:56
And yet, one is a chimp,
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然而一個是黑猩猩的
00:59
and the other is a cow.
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另一個是乳牛的
01:01
Now maybe cows have a really rich
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或許乳牛有著
01:04
internal mental life and are so smart
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心靈極豐富的內在美
01:06
that they choose not to let us realize it,
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聰明到不讓我們發現這些
01:10
but we eat them.
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但我們吃牠們
01:11
I think most people will agree
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我想大部分的人會同意
01:13
that chimps are capable of much more complex,
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黑猩猩比乳牛更有能力處理
01:15
elaborate and flexible behaviors than cows are.
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複雜、精細且有彈性的行為
01:18
So this is a first indication that the
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所以這意味著
01:20
"all brains are made the same way" scenario
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「所有腦都有相同的構造」的想法
01:22
is not quite right.
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不完全正確
01:24
But let's play along.
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但先讓我們繼續下去
01:25
If all brains were made the same way
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如果所有腦的構造都是一樣的
01:27
and you were to compare animals
with brains of different sizes,
with brains of different sizes,
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你比較動物之間不同大小的腦
01:30
larger brains should always have more neurons
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那較大的腦就該有較多的神經元
01:32
than smaller brains,
and the larger the brain,
and the larger the brain,
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腦愈大的話
01:34
the more cognitively able its owner should be.
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其主人也該有較強的認知能力
01:37
So the largest brain around should also be
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所以世上最大的腦
01:39
the most cognitively able.
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都該有最強大的認知能力
01:42
And here comes the bad news:
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但壞消息來了
01:43
Our brain, not the largest one around.
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我們人類的腦不是最大的
01:46
It seems quite vexing.
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這聽起來有點傷腦筋
01:47
Our brain weighs between 1.2 and 1.5 kilos,
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我們人類的腦大約是 1.2~1.5 公斤
01:50
but elephant brains weigh between four and five kilos,
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但大象的腦是 4~5 公斤
01:54
and whale brains can weigh up to nine kilos,
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而鯨的腦重達 9 公斤
01:56
which is why scientists used to resort to saying
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這就是為何科學家總是說
02:01
that our brain must be special
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我們的腦一定是特別
02:03
to explain our cognitive abilities.
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這有便於解釋我們的認知能力
02:06
It must be really extraordinary,
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我們的腦一定是很非比尋常
02:09
an exception to the rule.
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排除在一般規則外
02:11
Theirs may be bigger, but ours is better,
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牠們的腦或許更大但我們的更好
02:14
and it could be better, for example,
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舉例來說
02:16
in that it seems larger than it should be,
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我們的腦比它應該有的樣子更大
02:18
with a much larger cerebral cortex
than we should have
than we should have
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而且依我們身軀的大小來看
02:21
for the size of our bodies.
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它有著超過應有的大腦皮質數量
02:22
So that would give us extra cortex
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這些「過多」的大腦皮質讓我們
02:24
to do more interesting things
than just operating the body.
than just operating the body.
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做出比操控身軀更多有趣的事情
02:27
That's because the size of the brain
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因為通常腦的大小
02:29
usually follows the size of the body.
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跟身材的大小有關係
02:31
So the main reason for saying that
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主要會說「我們的腦
02:33
our brain is larger than it should be
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比它應有的樣子更大」
02:35
actually comes from comparing ourselves
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是來自於
02:37
to great apes.
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我們跟大猩猩作的比較
02:39
Gorillas can be two to three times larger than we are,
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大猩猩的身材比我們大上二到三倍
02:41
so their brains should also be larger than ours,
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所以牠們的腦也該比我們的大才對
02:44
but instead it's the other way around.
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事實上卻相反
02:46
Our brain is three times larger than a gorilla brain.
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我們的腦比大猩猩的大上三倍
02:49
The human brain also seems special
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從能量消耗的角度來看
02:51
in the amount of energy that it uses.
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人類的腦也是很特別的
02:53
Although it weighs only two percent of the body,
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雖然腦只佔身體重量的 2%
02:56
it alone uses 25 percent of all the energy
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光是它就消耗了身體
02:59
that your body requires to run per day.
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每天需要25% 的能量
03:02
That's 500 calories out of a total of 2,000 calories,
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也就是一天 2,000 卡路里中的 500 卡
03:05
just to keep your brain working.
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都是花在腦的運作上
03:07
So the human brain is larger than it should be,
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人腦不僅比它應有的大小還大
03:10
it uses much more energy than it should,
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且還消耗掉更多能量
03:12
so it's special.
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所以說它是特別的
03:14
And this is where the story started to bother me.
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這也是一開始困擾我的地方
03:16
In biology, we look for rules
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在生物學上我們尋找規則
03:18
that apply to all animals and to life in general,
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可以大體上適用於所有的動物和生命
03:21
so why should the rules of evolution
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但為什麼演化的規則
03:23
apply to everybody else but not to us?
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適用於所有生物，但不包括我們呢?
03:26
Maybe the problem was with the basic assumption
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或許問題就在於
03:29
that all brains are made in the same way.
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「所有腦的構造都是一樣的」這個假設上
03:30
Maybe two brains of a similar size
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或許兩個大小相近的腦
03:32
can actually be made of
very different numbers of neurons.
very different numbers of neurons.
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其實可以有著非常不同數量的神經元
03:35
Maybe a very large brain
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或許一個非常大的腦
03:36
does not necessarily have more neurons
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並不需要比一般大小的腦
03:38
than a more modest-sized brain.
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需要更多的神經元
03:40
Maybe the human brain
actually has the most neurons
actually has the most neurons
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或許不管人腦的大小
03:43
of any brain, regardless of its size,
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都比其他生物擁有最多的神經元
03:46
especially in the cerebral cortex.
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尤其是在大腦皮質這部分
03:48
So this to me became
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這些讓我想到一個
03:50
the important question to answer:
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待解答的重要問題：
03:51
how many neurons does the human brain have,
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人類的腦有多少神經元？
03:54
and how does that compare to other animals?
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答案可如何與其它動物做比較呢？
03:56
Now, you may have heard or read somewhere
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你可能聽過或在哪讀到
03:59
that we have 100 billion neurons,
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我們有一千億個神經元
04:01
so 10 years ago, I asked my colleagues
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十前年我問我的同事
04:03
if they knew where this number came from.
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知不知這數字哪來的
04:05
But nobody did.
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結果沒人知道
04:06
I've been digging through the literature
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我翻閱所有的文獻
04:08
for the original reference for that number,
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想找出這數字最原始的出處
04:10
and I could never find it.
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但我也沒辦法找到
04:11
It seems that nobody had actually ever counted
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看來似乎沒有人真正算出過
04:14
the number of neurons in the human brain,
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人類的腦究竟有多少個神經元
04:16
or in any other brain for that matter.
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其它的腦也一樣沒數出來過
04:18
So I came up with my own way
to count cells in the brain,
to count cells in the brain,
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所以我用自己的方法來數
04:22
and it essentially consists of
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這方法基本上是
04:24
dissolving that brain into soup.
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把大腦溶解在一碗湯裡
04:27
It works like this:
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就像這樣
04:29
You take a brain, or parts of that brain,
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你拿出一個或部分的腦
04:32
and you dissolve it in detergent,
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用某種溶劑溶解它
04:34
which destroys the cell membranes
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破壞掉細胞壁
04:35
but keeps the cell nuclei intact,
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但保留細胞核完整
04:38
so you end up with a suspension of free nuclei
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這樣你就有自由懸浮的細胞核
04:41
that looks like this,
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看起來就會像這樣
04:43
like a clear soup.
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一碗清湯
04:44
This soup contains all the nuclei
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這碗湯內有一隻鼠腦
04:46
that once were a mouse brain.
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所有的細胞核
04:48
Now, the beauty of a soup is that because it is soup,
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這碗湯的好處就在於因為它是一碗湯
04:51
you can agitate it and make those nuclei
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你可攪動它
04:54
be distributed homogeneously in the liquid,
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讓細胞核均勻散布在液體中
04:56
so that now by looking under the microscope
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然後只需要在顯微鏡之下
04:58
at just four or five samples
of this homogeneous solution,
of this homogeneous solution,
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觀察這碗湯中四到五個樣本
05:02
you can count nuclei, and therefore tell
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數算細胞核的數量
05:05
how many cells that brain had.
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就可得知這個腦有多少個細胞了
05:06
It's simple, it's straightforward,
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這既簡單又直接
05:08
and it's really fast.
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而且迅速
05:09
So we've used that method to count neurons
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所以我們利用這方法
05:11
in dozens of different species so far,
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計數十種不同物種的神經元
05:14
and it turns out that all brains
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得到的結果是
05:15
are not made the same way.
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所有的腦都不具有相同的構造
05:18
Take rodents and primates, for instance:
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以嚙齒動物和靈長類為例
05:20
In larger rodent brains, the average size
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較大隻的嚙齒動物腦中
05:22
of the neuron increases,
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其神經元的平均大小變大
05:24
so the brain inflates very rapidly
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腦就可迅速變大
05:27
and gains size much faster than it gains neurons.
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腦變大的速度比增加神經元快
05:30
But primate brains gain neurons
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但靈長類的腦
05:32
without the average neuron becoming any larger,
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可在神經元沒有變大的情況下增加數量
05:34
which is a very economical way
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這使得增加腦的神經元數量上
05:35
to add neurons to your brain.
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變得非常有效率
05:37
The result is that a primate brain
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結果顯示同樣大小的腦
05:39
will always have more neurons than
a rodent brain of the same size,
a rodent brain of the same size,
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靈長類的神經元數量都會超過嚙齒類的
05:42
and the larger the brain,
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而且腦愈大
05:44
the larger this difference will be.
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這差異就顯得愈大
05:46
Well, what about our brain then?
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那我們的腦呢？
05:48
We found that we have, on average,
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平均來講
05:50
86 billion neurons,
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我們有 860億個神經元
05:51
16 billion of which are in the cerebral cortex,
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其中的 160億都在大腦皮質裡
05:54
and if you consider that the cerebral cortex
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如果你認為大腦皮質
05:56
is the seat of functions like
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的功能中心是像
06:00
awareness and logical and abstract reasoning,
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認知 、邏輯 、抽象理解力
06:03
and that 16 billion is the most neurons
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那腦皮層中的160億就比其他
06:06
that any cortex has,
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任何大腦皮質擁有最多的數量了
06:08
I think this is the simplest explanation
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我認為這是我們人類卓越的認知能力
06:10
for our remarkable cognitive abilities.
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最簡單的解釋了
06:13
But just as important is what
the 86 billion neurons mean.
the 86 billion neurons mean.
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同樣重要的是這860億個神經元意味著什?
06:16
Because we found that the relationship
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因為我們發現到
06:18
between the size of the brain
and its number of neurons
and its number of neurons
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腦的大小和神經元數量的關係
06:20
could be described mathematically,
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可以用數學的方式描述
06:22
we could calculate what a human brain
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我們可計算出
06:24
would look like if it was made like a rodent brain.
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如果人腦的構造像嚙齒動物的會怎麼樣呢?
06:27
So, a rodent brain with 86 billion neurons
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若嚙齒動物的腦有 860億的神經元
06:30
would weigh 36 kilos.
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體重就會重達 36公斤
06:33
That's not possible.
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這是不可能的事情
06:35
A brain that huge would be crushed
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這麼大的一個腦
06:37
by its own weight,
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會被自己的重量壓垮
06:38
and this impossible brain would go
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要這麼重大的腦
06:40
in the body of 89 tons.
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搭配一個 89公噸的身體
06:44
I don't think it looks like us.
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是件讓我難以想像的東西
06:46
So this brings us to a very important
conclusion already,
conclusion already,
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這為我們今天下一個很重要的結論
06:48
which is that we are not rodents.
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我們不是嚙齒動物
06:51
The human brain is not a large rat brain.
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人腦沒有嚙齒動物搬的大腦
06:54
Compared to a rat, we might seem special, yes,
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比起老鼠我們的看起來特別多了
06:57
but that's not a fair comparison to make,
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但這樣比較並不公平
06:59
given that we know that we are not rodents.
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因為我們知道我們不是嚙齒動物
07:01
We are primates,
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我們是靈長類
07:02
so the correct comparison is to other primates.
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所以跟其它的靈長類動物作比較才正確
07:05
And there, if you do the math,
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所以計算一下的話
07:06
you find that a generic primate
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你會發現一般靈長類動物
07:09
with 86 billion neurons
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擁有860億的神經元
07:11
would have a brain of about 1.2 kilos,
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腦就會重約 1.2公斤
07:14
which seems just right,
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搭配重達 66公斤的身軀
07:16
in a body of some 66 kilos,
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看起來似乎合理
07:18
which in my case is exactly right,
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這剛好是我自身的例子
07:21
which brings us to a very unsurprising
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這結果雖然一點也不意外
07:23
but still incredibly important conclusion:
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但還是下了一個很重要的結論：
07:26
I am a primate.
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我是靈長類動物
07:28
And all of you are primates.
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你們全部也是靈長類動物
07:30
And so was Darwin.
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達爾文也是
07:32
I love to think that Darwin
would have really appreciated this.
would have really appreciated this.
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我猜想達爾文也會很喜歡這項結論
07:35
His brain, like ours,
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他的腦跟我們一樣
07:37
was made in the image of other primate brains.
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構造都是與其它靈長類相同的
07:41
So the human brain may be remarkable, yes,
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沒錯，人腦或許較卓越
07:43
but it is not special in its number of neurons.
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但在神經元的數量方面就沒什特別的
07:46
It is just a large primate brain.
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它不過是大的靈長類的頭腦
07:48
I think that's a very humbling and sobering thought
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我想這是一個非常謙虛和中肯的想法
07:51
that should remind us of our place in nature.
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提醒我們在大自然中扮演的角色
07:54
Why does it cost so much energy, then?
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為何它會消耗如此多的能量？
07:56
Well, other people have figured out
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有人已經估算出
07:58
how much energy the human brain
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人類和其它動物的腦
07:59
and that of other species costs,
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所消耗的能量
08:01
and now that we knew how many neurons
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現在了解每種腦有多少神經元
08:02
each brain was made of, we could do the math.
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我們就可做些計算
08:05
And it turns out that both human
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結果發現人類和其它動物的腦
08:07
and other brains cost about the same,
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消耗方式差不多一樣
08:09
an average of six calories
per billion neurons per day.
per billion neurons per day.
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每天平均每 10億個神經元消耗 6卡
08:13
So the total energetic cost of a brain
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一個腦所消耗的能量
08:15
is a simple, linear function
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2034
和它的神經元數量
08:17
of its number of neurons,
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成了一個簡單的線性關係
08:19
and it turns out that the human brain
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所以人腦消耗的能量
08:21
costs just as much energy as you would expect.
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就跟你估算的一樣多
08:25
So the reason why the human brain
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所以人腦為什麼
08:27
costs so much energy is simply because
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會消耗許多能量
08:28
it has a huge number of neurons,
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1983
單純是因為它有較多神經元的關係
08:30
and because we are primates
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作為靈長類
08:32
with many more neurons for a given body size
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比起身體大小類似的動物
08:34
than any other animal,
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我們擁有更多的神經元
08:36
the relative cost of our brain is large,
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腦也就消耗較多能量
08:39
but just because we're primates,
not because we're special.
not because we're special.
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這單純是因為我們是靈長類動物的關係
不是因為我們特別
不是因為我們特別
08:42
Last question, then:
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最後一個問題：
08:44
how did we come by this
remarkable number of neurons,
remarkable number of neurons,
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我們是如何有這麼多的神經元？
08:47
and in particular, if great apes
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515278
1900
明確地說
08:49
are larger than we are,
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1555
如果大猩猩身體比我們大
08:50
why don't they have a larger brain
than we do, with more neurons?
than we do, with more neurons?
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3765
為何沒有較大的腦和更多的神經元呢？
08:54
When we realized how much expensive it is
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2090
當理解到擁有許多神經元的同時
08:56
to have a lot of neurons in the brain, I figured,
228
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2333
也就需要燃燒更多的能量時
08:58
maybe there's a simple reason.
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2003
我推測或許這就是原因－
09:00
They just can't afford the energy
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1683
大猩猩無法同時供給能量
09:02
for both a large body
and a large number of neurons.
and a large number of neurons.
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應付龐大的身軀和大量的神經元
09:05
So we did the math.
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我們計算過
09:06
We calculated on the one hand
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1600
一方面計算出
09:08
how much energy a primate gets per day
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536586
1941
大猩猩一天從食物中
09:10
from eating raw foods,
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1350
獲得多少能量
09:11
and on the other hand, how much energy
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2037
另一方面計算
09:13
a body of a certain size costs
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特定大小的身軀要消耗多少能量
09:15
and how much energy a brain of a
certain number of neurons costs,
certain number of neurons costs,
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3387
還有一定數量的神經元所消耗的能量
09:19
and we looked for the combinations
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1489
然後我們一併查看
09:20
of body size and number of brain neurons
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2411
如果牠一天進食固定的時數
09:22
that a primate could afford
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牠可以提供多少能量
09:24
if it ate a certain number of hours per day.
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給多大的身軀和多少的神經元數量
09:26
And what we found is that
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我們發現到
09:28
because neurons are so expensive,
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1712
因為神經元消耗太多
09:30
there is a tradeoff between
body size and number of neurons.
body size and number of neurons.
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3370
這是身軀大小和神經元數量之間的妥協
09:33
So a primate that eats eight hours per day
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2951
一個靈長類一天進食八小時
09:36
can afford at most 53 billion neurons,
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3024
可提供最多 530億個神經元的能量
09:39
but then its body cannot be any bigger
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1727
但同時牠的身軀無法超過
09:41
than 25 kilos.
249
569383
1954
25公斤
09:43
To weigh any more than that,
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1701
如果增加體重
09:45
it has to give up neurons.
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則須捨棄神經元
09:46
So it's either a large body
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2653
所以只能單單擁有龐大的身軀
09:49
or a large number of neurons.
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或只能單單擁有大量的神經元
09:50
When you eat like a primate,
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如果你像靈長類一樣進食
09:52
you can't afford both.
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你無法同時有這兩項
09:54
One way out of this metabolic limitation
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1964
跳脫這限制的其中一個方法
09:56
would be to spend even more hours per day eating,
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是每天花更多時間進食
09:59
but that gets dangerous,
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1363
但這會提高危險
10:01
and past a certain point, it's just not possible.
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2719
所以這方法行不通
10:04
Gorillas and orangutans, for instance,
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1537
以大猩猩和紅毛猩猩為例
10:05
afford about 30 billion neurons
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1923
為了養活大約 300億個神經元
10:07
by spending eight and a half hours per day eating,
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每天要花8.5小時進食
10:10
and that seems to be about as much as they can do.
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這已經是它們所能做的了
10:13
Nine hours of feeding per day
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每天進食九小時
10:15
seems to be the practical limit for a primate.
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應是靈長類的極限
10:18
What about us?
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那我們呢？
10:20
With our 86 billion neurons
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我們有 860億個神經元
10:21
and 60 to 70 kilos of body mass,
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體重約 60~70公斤
10:25
we should have to spend over nine hours
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3561
我們每一天應該都要
10:28
per day every single day feeding,
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花超過九小時在進食上
10:32
which is just not feasible.
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2039
但這不可行
10:34
If we ate like a primate,
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1834
如果我們像靈長類一樣的吃
10:36
we should not be here.
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我們就不會在這裡了
10:38
How did we get here, then?
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那我們是怎麼辦到的？
10:40
Well, if our brain costs just as much energy
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2735
如果我們的腦真的需要大量的能量應付
10:43
as it should, and if we can't spend
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1723
而且又不能花每個
10:44
every waking hour of the day feeding,
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3674
清醒的時刻在進食上
10:48
then the only alternative, really,
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1911
另一個替代方式就是
10:50
is to somehow get more energy
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1958
從同樣的食物中
10:52
out of the same foods.
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1953
用某種方式得到更多能量
10:54
And remarkably, that matches exactly
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3800
很神奇的
10:58
what our ancestors are believed to have invented
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3037
這完全符合我們的假設－
11:01
one and a half million years ago,
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1839
150萬年前我們的祖先
11:03
when they invented cooking.
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2782
發明了烹煮
11:05
To cook is to use fire
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1970
烹煮是利用火
11:07
to pre-digest foods outside of your body.
286
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3800
在我們身外先消化好食物
11:11
Cooked foods are softer, so they're easier to chew
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煮過的食物較軟 易咀嚼
11:14
and to turn completely into mush in your mouth,
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2563
能在嘴裡完全嚼碎
11:16
so that allows them to be completely digested
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2152
好讓胃能夠完全消化
11:18
and absorbed in your gut,
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1436
供你吸收
11:20
which makes them yield much more
energy in much less time.
energy in much less time.
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3655
這樣就能在較短的時間內獲取更多的能量
11:24
So cooking frees time for us to do
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2489
所以烹煮讓我們有更多的時間
11:26
much more interesting things with our day
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利用我們的時間和神經元
11:28
and with our neurons
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從事更多有趣的事情
11:30
than just thinking about food,
295
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1905
這樣就不用為了
11:31
looking for food, and gobbling down food
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1704
老是要找食物，趕著吃
11:33
all day long.
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1225
然後花掉一整天的時間
11:34
So because of cooking, what once was
298
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2499
也因為烹煮的關係
11:37
a major liability, this large,
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2353
讓這一度為了應付巨量神經元
11:39
dangerously expensive brain with a lot of neurons,
300
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3033
消耗能量過度的腦
11:42
could now become a major asset,
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2036
變成現在主要的資產
11:44
now that we could both afford
the energy for a lot of neurons
the energy for a lot of neurons
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3251
讓我們可以同時提供能量給大量神經元
11:48
and the time to do interesting things with them.
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2503
也能花時間利用它們從事有趣的事
11:50
So I think this explains why the human brain
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1974
所以我認為這說明了為何人腦
11:52
grew to become so large so fast in evolution,
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3240
能夠在演化中迅速變大
11:55
all of the while remaining just a primate brain.
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3897
即便仍使用靈長類的腦
11:59
With this large brain now affordable by cooking,
307
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2774
也因為烹煮可養活這大腦的關係
12:02
we went rapidly from raw foods to culture,
308
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2913
我們很快速地從生食發展到養殖
12:05
agriculture, civilization, grocery stores,
309
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2606
農、文明、雜貨店
12:07
electricity, refrigerators,
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1625
電力、電冰箱
12:09
all of those things that nowadays
311
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1607
現今的這一切
12:11
allow us to get all the energy we need
312
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讓我們可以在
12:13
for the whole day in a single sitting
313
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2782
喜歡的速食店內一次消費
12:16
at your favorite fast food joint.
314
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2954
支撐一整天所需的能量
12:18
So what once was a solution
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2437
而過去的解決之道
12:21
now became the problem,
316
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1699
卻成了當今的問題
12:23
and ironically, we look for the solution in raw food.
317
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很諷刺地，我們在生食中尋求解答
12:28
So what is the human advantage?
318
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那人類的優勢是什麼？
12:31
What is it that we have
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1503
我們擁有什麼
12:32
that no other animal has?
320
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2535
其它動物沒有的呢?
12:35
My answer is that we have the largest number
321
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2348
我們的大腦皮質成了答案
12:37
of neurons in the cerebral cortex,
322
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1472
它擁有最多的神經元
12:39
and I think that's the simplest explanation
323
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1844
我想這為我們卓越的認知能力
12:40
for our remarkable cognitive abilities.
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2013
提供了簡單好懂的解釋
12:42
And what is it that we do that no other animal does,
325
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3227
那是什麼讓我們做其它動物做不到的呢?
12:46
and which I believe was fundamental
326
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1969
我認為最基本的方式
12:48
to allow us to reach that large,
327
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3083
讓我們擁有卓越大腦
12:51
largest number of neurons in the cortex?
328
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2222
且含大量神經元的大腦皮質
12:53
In two words, we cook.
329
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2215
只有歸於兩個字－ 烹煮
12:55
No other animal cooks its food. Only humans do.
330
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3566
其它動物不會煮食物，只有人類會
12:59
And I think that's how we got to become human.
331
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我認為這就是為何我們身為人類
13:02
Studying the human brain changed
the way I think about food.
the way I think about food.
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研究人腦改變我對食物的看法
13:04
I now look at my kitchen,
333
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現在我看著我的廚房
13:06
and I bow to it,
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都跟它敬禮
13:07
and I thank my ancestors for coming up
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1705
我感謝我的祖先
13:09
with the invention that probably made us humans.
336
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發明這些讓我們得以成為人類
13:11
Thank you very much.
337
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謝謝大家
13:13
(Applause)
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(鼓掌)
ABOUT THE SPEAKER
Suzana Herculano-Houzel - NeuroscientistSuzana Herculano-Houzel shrunk the human brain by 14 billion neurons -- by developing a new way to count them.
Why you should listen
How many neurons make a human brain? For years, the answer has been (give or take) 100 billion. But neuroscientist Suzana Herculano-Houzel decided to count them herself. Her research approach involved dissolving four human brains (donated to science) into a homogeneous mixture -- in her lab at the Institute of Biomedical Sciences in Rio de Janeiro, they call it "brain soup." She then took a sample of the mix, counted the number of cell nuclei belonging to neurons, and scaled that up. Result: the human brain has about 86 billion neurons, 14 billion fewer than assumed -- but intriguingly, far more than other animals, relative to brain size.
She suggests that it was the invention of cooking by our ancestors -- which makes food yield much more metabolic energy -- that allowed humans to develop the largest primate brain. She's now working on elephant and whale brains to test her hypothesis.
Suzana Herculano-Houzel | Speaker | TED.com