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

786,454 views ใƒป 2013-11-26

TED


ืื ื ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ืœืžื˜ื” ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ.

ืžืชืจื’ื: Boaz Hovav ืžื‘ืงืจ: Ido Dekkers
00:12
What is so special about the human brain?
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ืžื” ืžื™ื™ื—ื“ ืืช ื”ืžื•ื— ื”ืื ื•ืฉื™?
00:15
Why is it that we study other animals
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ืœืžื” ืื ื—ื ื• ื—ื•ืงืจื™ื ื‘ืขืœื™ ื—ื™ื™ื ืื—ืจื™ื
00:17
instead of them studying us?
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ื•ื”ื ืœื ื—ื•ืงืจื™ื ืื•ืชื ื•?
00:19
What does a human brain have or do
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ืžื” ื™ืฉ ืœืžื•ื— ื”ืื ื•ืฉื™ ืื• ืžื” ื”ื•ื ืขื•ืฉื”
00:21
that no other brain does?
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ืฉืืฃ ืžื•ื— ืื—ืจ ืœื ื™ื›ื•ืœ ืœืขืฉื•ืช?
00:23
When I became interested in these questions about 10 years ago,
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ื›ืฉื”ืชื—ืœืชื™ ืœื”ืชืขื ื™ื™ืŸ ื‘ืฉืืœื•ืช ื”ืœืœื•, ืœืคื ื™ ื›- 10 ืฉื ื™ื,
00:26
scientists thought they knew what different brains were made of.
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ื”ืขื•ืœื ื”ืžื“ืขื™ ื—ืฉื‘ ืฉื”ื•ื ื™ื•ื“ืข ืžืžื” ื‘ื ื•ื™ื™ื ืžื•ื—ื•ืช ืฉื•ื ื™ื.
00:28
Though it was based on very little evidence,
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ืœืžืจื•ืช ืฉื”ื™ื” ืœื”ื ืžืขื˜ ืžืื“ ื‘ื™ืกื•ืก ืžื“ืขื™,
00:30
many scientists thought that all mammalian brains,
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ืžื“ืขื ื™ื ืจื‘ื™ื ื—ืฉื‘ื• ืฉืžื•ื—ื ืฉืœ ื›ืœ ื”ื™ื•ื ืงื™ื,
00:32
including the human brain,
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ื›ื•ืœืœ ื”ืžื•ื— ื”ืื ื•ืฉื™,
00:34
were made in the same way,
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ื‘ื ื•ื™ื™ื ื‘ืฆื•ืจื” ื“ื•ืžื”,
00:35
with a number of neurons that was always
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ืขื ืžืกืคืจ ืชืื™ ืžื•ื— ืฉืงืฉื•ืจ ื‘ืื•ืคืŸ ื™ืฉื™ืจ
00:37
proportional to the size of the brain.
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ืœื’ื•ื“ืœื• ืฉืœ ื”ืžื•ื—.
00:39
This means that two brains of the same size,
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ื”ืžืฉืžืขื•ืช ื”ื™ื ืฉืฉื ื™ ืžื•ื—ื•ืช ื‘ืขืœื™ ื’ื•ื“ืœ ื–ื”ื”,
00:41
like these two, with a respectable 400 grams,
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ื›ืžื• ืืœื• ื‘ืชืžื•ื ื”, ื”ืฉื•ืงืœื™ื 400 ื’ืจื,
00:45
should have similar numbers of neurons.
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ืžื›ื™ืœื™ื ื›ืžื•ืช ื“ื•ืžื” ืฉืœ ืชืื™ ืžื•ื— (ื ื•ื™ืจื•ื ื™ื).
00:47
Now, if neurons are the functional
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ืื ืชืื™ ื”ืžื•ื— ืžืชืคืงื“ื™ื
00:49
information processing units of the brain,
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ื›ื™ื—ื™ื“ื•ืช ืขื™ื‘ื•ื“ ื”ืžื™ื“ืข ืฉืœ ื”ืžื•ื—,
00:52
then the owners of these two brains
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ื”ืจื™ ืฉื‘ืขืœื™ื”ื ืฉืœ ืฉื ื™ ื”ืžื•ื—ื•ืช ื”ืœืœื•
00:54
should have similar cognitive abilities.
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ืฆืจื™ื›ื™ื ืœื”ื™ื•ืช ื‘ืขืœื™ ื™ื›ื•ืœื•ืช ืฉื›ืœื™ื•ืช ื“ื•ืžื•ืช.
00:56
And yet, one is a chimp,
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ืื‘ืœ, ืžื•ื— ืื—ื“ ื‘ืชืžื•ื ื” ืฉื™ื™ืš ืœืฉื™ืžืคื ื–ื”,
00:59
and the other is a cow.
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ื•ื”ืฉื ื™ ืœืคืจื”.
01:01
Now maybe cows have a really rich
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ื™ื™ืชื›ืŸ ืฉืœืคืจื•ืช ื™ืฉ ืขื•ืฉืจ ื’ื“ื•ืœ
01:04
internal mental life and are so smart
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ืฉืœ ื—ื™ื™ ืžื—ืฉื‘ื”, ื•ื”ืŸ ื›ื” ื—ื›ืžื•ืช
01:06
that they choose not to let us realize it,
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ืฉื”ืŸ ื‘ื•ื—ืจื•ืช ืœื ืœืืคืฉืจ ืœื ื• ืœื’ืœื•ืช ืืช ื—ื›ืžืชืŸ,
01:10
but we eat them.
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ื•ืžืขื“ื™ืคื•ืช ืฉื ืื›ืœ ืื•ืชืŸ.
01:11
I think most people will agree
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ืื‘ืœ ื ืจืื” ืœื™ ืฉืจื•ื‘ ื”ืื ืฉื™ื ื™ืกื›ื™ืžื•
01:13
that chimps are capable of much more complex,
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ืฉืœืฉื™ืžืคื ื–ื™ื ื™ืฉ ื™ื›ื•ืœืช ืœื”ืชื ื”ื’ ื‘ืจืžืช ืžื•ืจื›ื‘ื•ืช,
01:15
elaborate and flexible behaviors than cows are.
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ื”ื‘ื ืช ืคืจื˜ื™ื ื•ื’ืžื™ืฉื•ืช ืจื‘ื” ื™ื•ืชืจ ืžืœืคืจื•ืช.
01:18
So this is a first indication that the
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ื›ืš ืฉื™ืฉ ืœื ื• ืขื“ื•ืช ืจืืฉื•ื ื” ืฉื”ื’ื™ืฉื” ืฉื˜ื•ืขื ืช
01:20
"all brains are made the same way" scenario
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ืฉื›ืœ ื”ืžื•ื—ื•ืช ื‘ื ื•ื™ื™ื ื‘ืื•ืคืŸ ื–ื”ื”
01:22
is not quite right.
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ืื™ื ื ื” ื ื›ื•ื ื” ืžื™ืกื•ื“ื”.
01:24
But let's play along.
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ืื‘ืœ ื‘ื•ืื• ื ืžืฉื™ืš ืœื‘ื“ื•ืง ืื•ืชื”.
01:25
If all brains were made the same way
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ืื ื›ืœ ื”ืžื•ื—ื•ืช ื‘ื ื•ื™ื™ื ื‘ืื•ืคืŸ ื“ื•ืžื”
01:27
and you were to compare animals with brains of different sizes,
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ื•ื ืฉื•ื•ื” ื‘ื™ืŸ ื‘ืขืœื™ ื—ื™ื™ื ืฉื•ื ื™ื ืขื ืžื•ื—ื•ืช ื‘ื’ื•ื“ืœ ืฉื•ื ื”,
01:30
larger brains should always have more neurons
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ื‘ืžื•ื—ื•ืช ื’ื“ื•ืœื™ื ื™ื•ืชืจ ื ืฆืคื” ืœืžืฆื•ื ื™ื•ืชืจ ืชืื™ ืžื•ื—
01:32
than smaller brains, and the larger the brain,
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ื‘ื”ืฉื•ื•ืื” ืœืžื•ื—ื•ืช ืงื˜ื ื™ื ื™ื•ืชืจ, ื•ื›ื›ืœ ืฉื”ืžื•ื— ื’ื“ื•ืœ ื™ื•ืชืจ,
01:34
the more cognitively able its owner should be.
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ื ืฆืคื” ืœื™ื›ื•ืœื•ืช ืฉื›ืœื™ื•ืช ื’ื‘ื•ื”ื•ืช ื™ื•ืชืจ ืฉืœ ื‘ืขืœ ื”ื—ื™ื™ื.
01:37
So the largest brain around should also be
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ื›ืš ืฉื‘ืขืœ ื”ืžื•ื— ื”ื’ื“ืœ ื‘ื™ื•ืชืจ ื‘ื˜ื‘ืข ืืžื•ืจ ืœื”ื™ื•ืช
01:39
the most cognitively able.
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ื”ื—ื›ื ื‘ื™ื•ืชืจ.
01:42
And here comes the bad news:
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ื•ื”ื ื” ื”ื—ื“ืฉื•ืช ื”ืจืขื•ืช:
01:43
Our brain, not the largest one around.
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ื”ืžื•ื— ืฉืœื ื• ืื™ื ื• ื’ื“ื•ืœ ื‘ืžื™ื•ื—ื“.
01:46
It seems quite vexing.
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ื–ื” ืงืฆืช ืžื‘ื™ืš.
01:47
Our brain weighs between 1.2 and 1.5 kilos,
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ื”ืžื•ื— ื”ืื ื•ืฉื™ ืฉื•ืงืœ ื‘ื™ืŸ 1.2 ืœ- 1.5 ืง"ื’,
01:50
but elephant brains weigh between four and five kilos,
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ืœืขื•ืžืชื• ืฉื•ืงืœ ืžื•ื— ืฉืœ ืคื™ืœ ื‘ื™ืŸ 4 ืœ- 5 ืง"ื’
01:54
and whale brains can weigh up to nine kilos,
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ื•ืžื•ื— ืฉืœ ืœื•ื•ื™ื™ืชืŸ ืžื’ื™ืข ืœืžืฉืงืœ ืฉืœ 9 ืง"ื’,
01:56
which is why scientists used to resort to saying
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ืžื” ืฉื”ื•ื‘ื™ืœ ืืช ื”ืžื“ืขื ื™ื ืœื”ื›ื™ืจ ื‘ื›ืš
02:01
that our brain must be special
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ืฉื”ืžื•ื— ื”ืื ื•ืฉื™ ื—ื™ื™ื‘ ืœื”ื™ื•ืช ื‘ืขืœ ื™ื™ื—ื•ื“
02:03
to explain our cognitive abilities.
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ืฉืžืกื‘ื™ืจ ืืช ื”ื™ื›ื•ืœื•ืช ื”ืฉื›ืœื™ื•ืช ื”ื’ื‘ื•ื”ื•ืช ืฉืœื ื•.
02:06
It must be really extraordinary,
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ื”ื•ื ื—ื™ื™ื‘ ืœื”ื™ื•ืช ื™ื•ืฆื ื“ื•ืคืŸ,
02:09
an exception to the rule.
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ื—ื•ืจื’ ืžื—ื•ืงื™ ื”ื˜ื‘ืข.
02:11
Theirs may be bigger, but ours is better,
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ื”ืžื•ื— ืฉืœื”ื ื’ื“ื•ืœ ื™ื•ืชืจ, ืื‘ืœ ืฉืœื ื• ื˜ื•ื‘ ื™ื•ืชืจ,
02:14
and it could be better, for example,
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ื•ื™ืชื›ืŸ ืฉื”ืžื•ื— ืฉืœื ื• ื™ื•ืชืจ ื˜ื•ื‘, ืœื“ื•ื’ืžื”,
02:16
in that it seems larger than it should be,
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ื‘ื’ืœืœ ืฉื”ื•ื ื ืจืื” ื’ื“ื•ืœ ื™ื•ืชืจ ืžืžื” ืฉื”ื•ื ืืžื•ืจ ืœื”ื™ื•ืช,
02:18
with a much larger cerebral cortex than we should have
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ืขื ืงืœื™ืคืช ืžื•ื— ื‘ืฉื˜ื— ื’ื“ื•ืœ ื™ื•ืชืจ ืžื”ืฆืคื•ื™
02:21
for the size of our bodies.
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ื‘ื™ื—ืก ืœื’ื•ื“ืœ ื”ื’ื•ืฃ ืฉืœื ื•.
02:22
So that would give us extra cortex
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ื›ืš ืฉื™ืฉ ืœื ื• ืงืœื™ืคืช ืžื•ื— ืขื•ื“ืคืช
02:24
to do more interesting things than just operating the body.
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ืฉืžืืคืฉืจืช ืœื‘ืฆืข ื“ื‘ืจื™ื ื ื•ืกืคื™ื ื•ืžืขื ื™ื™ื ื™ื, ื•ืœื ืจืง ืœื”ืคืขื™ืœ ืืช ื”ื’ื•ืฃ.
02:27
That's because the size of the brain
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ืžืฉื•ื ืฉื’ื•ื“ืœ ื”ืžื•ื—
02:29
usually follows the size of the body.
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ืงืฉื•ืจ ื‘ื“"ื› ื‘ืื•ืคืŸ ื™ืฉื™ืจ ืœื’ื•ื“ืœ ื”ื’ื•ืฃ.
02:31
So the main reason for saying that
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ื›ืš ืฉื”ืกื™ื‘ื” ื”ืขื™ืงืจื™ืช ืœืืžื™ืจื” ืœืคื™ื”
02:33
our brain is larger than it should be
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ื”ืžื•ื— ื”ืื ื•ืฉื™ ื’ื“ื•ืœ ืžื”ืฆืคื•ื™
02:35
actually comes from comparing ourselves
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ื ื•ื‘ืขืช ืœืžืขืฉื” ืžื”ืฉื•ื•ืื” ืฉืœ ื‘ื ื™ ื”ืื“ื
02:37
to great apes.
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ืœืงื•ืคื™ ื”ืื“ื ื”ื’ื“ื•ืœื™ื.
02:39
Gorillas can be two to three times larger than we are,
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ื”ื’ื•ืจื™ืœื•ืช ืžื’ื™ืขื•ืช ืœื’ื•ื“ืœ ื›ืคื•ืœ ื•ืืคื™ืœื• ืžืฉื•ืœืฉ ื‘ื”ืฉื•ื•ืื” ืœืื“ื
02:41
so their brains should also be larger than ours,
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ื›ืš ืฉืžื•ื—ืŸ ืฆืคื•ื™ ืœื”ื™ื•ืช ื’ื“ื•ืœ ื™ื•ืชืจ ืžืฉืœื ื•,
02:44
but instead it's the other way around.
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ืื‘ืœ ื‘ืคื•ืขืœ ื–ื” ื”ืคื•ืš.
02:46
Our brain is three times larger than a gorilla brain.
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ื”ืžื•ื— ืฉืœื ื• ื’ื“ื•ืœ ืžืžื•ื—ืŸ ืฉืœ ื”ื’ื•ืจื™ืœื•ืช ืคื™ 3.
02:49
The human brain also seems special
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ื”ืžื•ื— ื”ืื ื•ืฉื™ ื ืจืื” ื—ืจื™ื’
02:51
in the amount of energy that it uses.
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ื’ื ื‘ื›ืžื•ืช ื”ืื ืจื’ื™ื” ืฉื”ื•ื ืฆื•ืจืš.
02:53
Although it weighs only two percent of the body,
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ืœืžืจื•ืช ืฉื”ื•ื ืฉื•ืงืœ ืจืง ื›- 2% ืžืžืฉืงืœ ื”ื’ื•ืฃ,
02:56
it alone uses 25 percent of all the energy
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ื”ื•ื ืžื ืฆืœ ื›- 25% ืžื”ืื ืจื’ื™ื”
02:59
that your body requires to run per day.
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ืฉื’ื•ืคื ื• ืฆื•ืจืš ื‘ืžื”ืœืš ื”ื™ืžืžื”.
03:02
That's 500 calories out of a total of 2,000 calories,
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ื‘ืขืจืš 500 ืงืœื•ืจื™ื•ืช ืžืชื•ืš ืฆืจื™ื›ื” ื™ื•ืžื™ืช ืฉืœ 2,000 ืงืœื•ืจื™ื•ืช,
03:05
just to keep your brain working.
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ื ืฆืจื›ื™ื ืข"ื™ ื”ืžื•ื— ืœื‘ื“ื•.
03:07
So the human brain is larger than it should be,
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ื”ืžื•ื— ื”ืื ื•ืฉื™ ื’ื“ื•ืœ ืžื”ืฆืคื•ื™,
03:10
it uses much more energy than it should,
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ื”ื•ื ืฆื•ืจืš ื™ื•ืชืจ ืžื“ื™ ืื ืจื’ื™ื”,
03:12
so it's special.
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ืœื›ืŸ ื”ื•ื ืžื™ื•ื—ื“.
03:14
And this is where the story started to bother me.
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ื•ื›ืืŸ ื”ื’ื™ืข ื”ื—ืœืง ืฉื”ื˜ืจื™ื“ ืื•ืชื™.
03:16
In biology, we look for rules
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ื‘ื‘ื™ื•ืœื•ื’ื™ื”, ืื ื—ื ื• ืžื—ืคืฉื™ื ื—ื•ืงื™ื
03:18
that apply to all animals and to life in general,
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ืฉื—ืœื™ื ืขืœ ื›ืœ ื‘ืขืœื™ ื”ื—ื™ื™ื ื‘ืœื™ ื™ื•ืฆื ืžืŸ ื”ื›ืœืœ,
03:21
so why should the rules of evolution
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ื•ืœื ื”ื‘ื ืชื™ ืžื“ื•ืข ื—ื•ืงื™ ื”ืื‘ื•ืœื•ืฆื™ื”
03:23
apply to everybody else but not to us?
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ื—ืœื™ื ืขืœ ื›ืœ ื‘ืขืœื™ ื”ื—ื™ื™ื ื•ืœื ืขืœ ื‘ื ื™ ื”ืื“ื?
03:26
Maybe the problem was with the basic assumption
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ืื•ืœื™ ื”ื‘ืขื™ื” ื ื•ื‘ืขืช ืžื”ื ื—ืช ื”ื™ื™ืกื•ื“
03:29
that all brains are made in the same way.
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ืฉื›ืœ ื”ืžื•ื—ื•ืช ื‘ื ื•ื™ื™ื ื‘ืื•ืคืŸ ื–ื”ื”.
03:30
Maybe two brains of a similar size
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ืื•ืœื™ ืฉื ื™ ืžื•ื—ื•ืช ื‘ืขืœื™ ื’ื•ื“ืœ ื–ื”ื”
03:32
can actually be made of very different numbers of neurons.
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ืขืฉื•ื™ื™ื ืœื”ื›ื™ืœ ืžืกืคืจ ืชืื™ ืžื•ื— ืฉื•ื ื” ืžืื“.
03:35
Maybe a very large brain
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ืื•ืœื™ ืžื•ื— ื’ื“ื•ืœ ืžืื“
03:36
does not necessarily have more neurons
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ืœื ืžื›ื™ืœ ื™ื•ืชืจ ืชืื™ ืžื•ื—
03:38
than a more modest-sized brain.
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ืžืžื•ื— ืงื˜ืŸ ื™ื•ืชืจ.
03:40
Maybe the human brain actually has the most neurons
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ืื•ืœื™ ื”ืžื•ื— ื”ืื ื•ืฉื™ ืžื›ื™ืœ ื™ื•ืชืจ ืชืื™ ืžื•ื—
03:43
of any brain, regardless of its size,
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ืžื›ืœ ืžื•ื— ืื—ืจ, ื‘ืœื™ ืงืฉืจ ืœื’ื•ื“ืœื•,
03:46
especially in the cerebral cortex.
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ื‘ืขื™ืงืจ ื‘ืื–ื•ืจ ืงืœื™ืคืช ื”ืžื•ื—.
03:48
So this to me became
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ื›ืš ืฉืขื‘ื•ืจื™
03:50
the important question to answer:
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ื”ืฉืืœื” ื”ื ื›ื•ื ื” ืขืœื™ื” ืฆืจื™ืš ืœืขื ื•ืช ื”ื™ื™ืชื”:
03:51
how many neurons does the human brain have,
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ื›ืžื” ืชืื™ ืžื•ื— ื™ืฉ ื‘ืžื•ื— ื”ืื ื•ืฉื™,
03:54
and how does that compare to other animals?
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ื•ื›ืžื” ื™ืฉ ืœื‘ืขืœื™ ื—ื™ื™ื ืื—ืจื™ื?
03:56
Now, you may have heard or read somewhere
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ื™ืชื›ืŸ ืฉืฉืžืขืชื ืื• ืงืจืืชื ืื™ืคืฉื”ื•
03:59
that we have 100 billion neurons,
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ืฉื”ืžื•ื— ืฉืœื ื• ืžื›ื™ืœ ื›- 100 ืžื™ืœื™ืืจื“ ืชืื™ ืžื•ื—,
04:01
so 10 years ago, I asked my colleagues
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ืื– ืœืคื ื™ 10 ืฉื ื™ื ืฉืืœืชื™ ืืช ื”ืขืžื™ืชื™ื ืฉืœื™
04:03
if they knew where this number came from.
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ืื ื”ื ื™ื•ื“ืขื™ื ืžื” ืžืงื•ืจ ื”ืžืกืคืจ ื”ื–ื”?
04:05
But nobody did.
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ืืฃ ืื—ื“ ืœื ื™ื“ืข.
04:06
I've been digging through the literature
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ื—ื™ืคืฉืชื™ ื‘ืกืคืจื•ืช ื”ืจืคื•ืื™ืช
04:08
for the original reference for that number,
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ืื—ืจื™ ื”ืžืืžืจ ื”ืžืงื•ืจื™ ืฉื ืงื‘ ื‘ืžืกืคืจ ื”ื–ื”,
04:10
and I could never find it.
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ื•ืœื ืžืฆืืชื™ ืื•ืชื•.
04:11
It seems that nobody had actually ever counted
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ืžืกืชื‘ืจ ืฉืืฃ ืื—ื“ ืœื ืกืคืจ ื‘ืืžืช
04:14
the number of neurons in the human brain,
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ืืช ืžืกืคืจ ืชืื™ ื”ืžื•ื— ื‘ืžื•ื— ื”ืื ื•ืฉื™,
04:16
or in any other brain for that matter.
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ืื• ื‘ืžื•ื— ืฉืœ ื‘ืขืœื™ ื—ื™ื™ื ืื—ืจื™ื.
04:18
So I came up with my own way to count cells in the brain,
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ืื– ื”ืžืฆืืชื™ ืฉื™ื˜ื” ืžืฉืœื™ ืขืœ ืžื ืช ืœืกืคื•ืจ ืืช ื”ืชืื™ื ื‘ืžื•ื—,
04:22
and it essentially consists of
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ื”ืฉื™ื˜ื” ืžืชื‘ืกืกืช ืขืœ
04:24
dissolving that brain into soup.
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ื”ืžืกืช ื”ืžื•ื— ืœืžืขื™ื™ืŸ ืžึทืจึธืง.
04:27
It works like this:
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ื•ื›ืš ื–ื” ืขื•ื‘ื“:
04:29
You take a brain, or parts of that brain,
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ืœื•ืงื—ื™ื ืžื•ื—, ืื• ื—ืœืง ืžืžื•ื—,
04:32
and you dissolve it in detergent,
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ื•ืžืžื™ืกื™ื ืื•ืชื• ื‘ืกื‘ื•ืŸ,
04:34
which destroys the cell membranes
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ืฉื”ื•ืจืก ืืช ืงืจื•ืžื™ ื”ืชืื™ื
04:35
but keeps the cell nuclei intact,
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ืื‘ืœ ืœื ืคื•ื’ืข ื‘ื’ืจืขื™ื ื™ ื”ืชืื™ื,
04:38
so you end up with a suspension of free nuclei
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ื›ืš ืฉืžืชืงื‘ืœ ื ื•ื–ืœ ืขื ื’ืจืขื™ื ื™ ืชืื™ื ื—ื•ืคืฉื™ื™ื
04:41
that looks like this,
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ืฉื ืจืื” ื›ืš,
04:43
like a clear soup.
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ื›ืžื• ืžืจืง ืฆื—.
04:44
This soup contains all the nuclei
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ื”ืžืจืง ื”ื–ื” ืžื›ื™ืœ ืืช ื›ืœ ื’ืจืขื™ื ื™ ื”ืชืื™ื
04:46
that once were a mouse brain.
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ืฉื‘ืžื•ื—ื• ืฉืœ ืขื›ื‘ืจ.
04:48
Now, the beauty of a soup is that because it is soup,
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ื”ื™ืชืจื•ืŸ ืฉืœ ื”ืžืจืง ื”ื•ื ืฉื‘ื”ื™ื•ืชื• ืžืจืง,
04:51
you can agitate it and make those nuclei
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ื ื™ืชืŸ ืœื ืขืจ ืื•ืชื• ืขื“ ืœืžืฆื‘ ื‘ื• ื’ืจืขื™ื ื™ ื”ืชืื™ื
04:54
be distributed homogeneously in the liquid,
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ืžืคื•ื–ืจื™ื ื‘ืื•ืคืŸ ืฉื•ื•ื” ื‘ื ื•ื–ืœ,
04:56
so that now by looking under the microscope
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ื›ืš ืฉืื ื ื‘ื“ื•ืง ืืช ื”ืžืจืง ื‘ืžื™ืงืจื•ืกืคืงื•ืค
04:58
at just four or five samples of this homogeneous solution,
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ื•ื ื‘ื™ื˜ ื‘- 4 ืื• 5 ื“ื’ื™ืžื•ืช ืžื”ื ื•ื–ืœ,
05:02
you can count nuclei, and therefore tell
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ื ื•ื›ืœ ืœืกืคื•ืจ ื‘ื”ื ืืช ืžืกืคืจ ื’ืจืขื™ื ื™ ื”ืชืื™ื, ื•ืœื—ืฉื‘
05:05
how many cells that brain had.
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ื›ืžื” ืชืื™ื ื™ืฉ ื‘ืžื•ื— ื›ื•ืœื•.
05:06
It's simple, it's straightforward,
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ื–ื” ืคืฉื•ื˜, ื–ื” ื™ืฉื™ืจ,
05:08
and it's really fast.
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ื•ื–ื” ืžื”ื™ืจ ืžืื“.
05:09
So we've used that method to count neurons
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ื”ืฉืชืžืฉื ื• ื‘ืฉื™ื˜ื” ื›ื“ื™ ืœืกืคื•ืจ ืชืื™ ืžื•ื—
05:11
in dozens of different species so far,
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ื‘ืขืฉืจื•ืช ืžื™ื ื™ ื‘ืขืœื™ ื—ื™ื™ื ืขื“ ื›ื”,
05:14
and it turns out that all brains
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ื•ืžืชื‘ืจืจ ืฉื›ืœ ื”ืžื•ื—ื•ืช
05:15
are not made the same way.
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ืœื ื‘ื ื•ื™ื™ื ื‘ืื•ืคืŸ ื“ื•ืžื”.
05:18
Take rodents and primates, for instance:
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ืงื—ื• ืžื›ืจืกืžื™ื ื•ืงื•ืคื™ื ืžืžืฉืคื—ืช ื”ืงื•ืคืื™ื (ืคืจื™ืžึทื˜ื™ื) ืœื“ื•ื’ืžื”:
05:20
In larger rodent brains, the average size
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ื‘ืžื•ื—ื•ืช ืžื›ืจืกืžื™ื ื”ื’ื“ื•ืœื™ื ื™ื•ืชืจ, ื”ื’ื•ื“ืœ ื”ืžืžื•ืฆืข
05:22
of the neuron increases,
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ืฉืœ ืชืื™ ื”ืžื•ื— ื”ื‘ื•ื“ื“ื™ื ื’ื“ืœ,
05:24
so the brain inflates very rapidly
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ื›ืš ืฉื”ืžื•ื—ื•ืช ืžืชื ืคื—ื™ื ืžื”ืจ
05:27
and gains size much faster than it gains neurons.
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ื•ื’ื“ืœื™ื ื‘ื ืคื—ื ืžื”ืจ ื™ื•ืชืจ ืžืงืฆื‘ ื”ื’ื™ื“ื•ืœ ื‘ืžืกืคืจ ืชื ื”ืžื•ื—.
05:30
But primate brains gain neurons
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ืื‘ืœ ืžื•ื—ื•ืช ืฉืœ ืงื•ืคื™ื ืžื•ืกื™ืคื™ื ืชืื™ ืžื•ื—
05:32
without the average neuron becoming any larger,
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ื‘ืœื™ ืขืœื™ื” ื‘ื’ื•ื“ืœื• ืฉืœ ืชื ืžื•ื— ื‘ื•ื“ื“,
05:34
which is a very economical way
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ืžื“ื•ื‘ืจ ื‘ืฉื™ื˜ื” ื—ืกื›ื•ื ื™ืช ืžืื“,
05:35
to add neurons to your brain.
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ืœื”ื•ืกื™ืฃ ืชืื™ ืžื•ื—.
05:37
The result is that a primate brain
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ื›ืชื•ืฆืื” ืžื›ืš ืžื•ื—ื•ืช ื”ืงื•ืคื™ื
05:39
will always have more neurons than a rodent brain of the same size,
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ืชืžื™ื“ ื™ื›ื™ืœื• ื™ื•ืชืจ ืชืื™ ืžื•ื— ืžืžื•ื—ื•ืช ืžื›ืจืกืžื™ื ื‘ืื•ืชื• ื”ื’ื•ื“ืœ,
05:42
and the larger the brain,
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ื•ื›ื›ืœ ืฉื”ืžื•ื— ื’ื“ื•ืœ ื™ื•ืชืจ,
05:44
the larger this difference will be.
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ื”ื”ื‘ื“ืœ ื’ื“ื•ืœ ื™ื•ืชืจ.
05:46
Well, what about our brain then?
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ื•ืžื” ืœื’ื‘ื™ ื”ืžื•ื— ื”ืื ื•ืฉื™?
05:48
We found that we have, on average,
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ืžืฆืื ื• ืฉืœื‘ื ื™ ื”ืื“ื ื™ืฉ, ื‘ืžืžื•ืฆืข,
05:50
86 billion neurons,
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86 ืžื™ืœื™ืืจื“ ืชืื™ ืžื•ื—,
05:51
16 billion of which are in the cerebral cortex,
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16 ืžื™ืœื™ืืจื“ ืžืชื•ื›ื ื ืžืฆืื™ื ื‘ืงืœื™ืคืช ื”ืžื•ื—,
05:54
and if you consider that the cerebral cortex
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ื•ืื ืžื‘ื™ืื™ื ื‘ื—ืฉื‘ื•ืŸ ืืช ื”ืขื•ื‘ื“ื” ืฉืงืœื™ืคืช ืžื•ื—
05:56
is the seat of functions like
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ืžืื›ืœืกืช ืชืคืงื•ื“ื™ื ื—ืฉื•ื‘ื™ื ื›ืžื•
06:00
awareness and logical and abstract reasoning,
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ืžื•ื“ืขื•ืช, ื—ืฉื™ื‘ื” ืœื•ื’ื™ืช ื•ื—ืฉื™ื‘ื” ืžื•ืคืฉื˜ืช,
06:03
and that 16 billion is the most neurons
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ื•ืฉ- 16 ืžื™ืœื™ืืจื“ ืชืื™ ืžื•ื— ืžื”ื•ื•ื” ืฉื™ื
06:06
that any cortex has,
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ืœื›ืžื•ืช ืชืื™ ืžื•ื— ื‘ื›ืœ ืงืœื™ืคืช ืžื•ื— ื‘ื›ืœ ื‘ืขืœื™ ื”ื—ื™ื™ื,
06:08
I think this is the simplest explanation
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ื ืจืื” ืœื™ ืฉื–ื”ื• ื”ื”ืกื‘ืจ ื”ืคืฉื•ื˜ ื•ื”ื‘ืจื•ืจ ื‘ื™ื•ืชืจ
06:10
for our remarkable cognitive abilities.
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ืœื™ื›ื•ืœื•ืช ื”ืฉื›ืœื™ื•ืช ื™ื•ืฆืื•ืช ื”ื“ื•ืคืŸ ืฉืœ ื‘ื ื™ ื”ืื“ื.
06:13
But just as important is what the 86 billion neurons mean.
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ืื‘ืœ ื™ืฉ ื’ื ื—ืฉื™ื‘ื•ืช ืœืงื™ื•ืžื ืฉืœ 86 ืžื™ืœื™ืืจื“ ืชืื™ ืžื•ื—.
06:16
Because we found that the relationship
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ื›ื™ ืžืฆืื ื• ืฉื”ืงืฉืจ
06:18
between the size of the brain and its number of neurons
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ื‘ื™ืŸ ื’ื•ื“ืœ ื”ืžื•ื— ืœืžืกืคืจ ืชืื™ ื”ืžื•ื—
06:20
could be described mathematically,
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ื™ื›ื•ืœ ืœื”ื™ื•ืช ืžืชื•ืืจ ื‘ืื•ืคืŸ ืžืชืžื˜ื™,
06:22
we could calculate what a human brain
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ื™ื›ื•ืœื ื• ืœื—ืฉื‘ ื›ื™ืฆื“ ื™ืจืื” ืžื•ื— ืื ื•ืฉื™
06:24
would look like if it was made like a rodent brain.
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ืื ื”ื•ื ื™ื•ืจื›ื‘ ืžืชืื™ ืžื•ื— ืฉืœ ืžื›ืจืกื.
06:27
So, a rodent brain with 86 billion neurons
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ืžื•ื— ืฉืœ ืžื›ืจืกื ืขื 86 ืžื™ืœื™ืืจื“ ืชืื™ื
06:30
would weigh 36 kilos.
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ื™ืฉืงื•ืœ 36 ืง"ื’.
06:33
That's not possible.
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ื•ื–ื” ืœื ืืคืฉืจื™.
06:35
A brain that huge would be crushed
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ืžื•ื— ื‘ื’ื•ื“ืœ ื›ื–ื”
06:37
by its own weight,
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ื™ื™ืžื—ืฅ ืžื”ืžืฉืงืœ ื”ืขืฆืžื™ ืฉืœื•,
06:38
and this impossible brain would go
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ื•ืžื•ื— ื‘ืœืชื™ ืืคืฉืจื™ ื›ื–ื” ื™ืฆืจื™ืš ื’ื•ืฃ
06:40
in the body of 89 tons.
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ืฉืฉื•ืงืœ 89 ื˜ื•ืŸ.
06:44
I don't think it looks like us.
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ืื ื™ ืœื ื—ื•ืฉื‘ืช ืฉื”ื•ื ื™ืจืื” ื›ืžื•ื ื•.
06:46
So this brings us to a very important conclusion already,
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ืื– ืื ื• ืžืกื™ืงื™ื ืžืกืงื ื” ื—ืฉื•ื‘ื” ื›ื‘ืจ ืขื›ืฉื™ื•,
06:48
which is that we are not rodents.
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ืื ื—ื ื• ืœื ืžื›ืจืกืžื™ื.
06:51
The human brain is not a large rat brain.
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ื”ืžื•ื— ื”ืื ื•ืฉื™ ืื™ื ื• ืžื•ื— ืฉืœ ืขื›ื‘ืจ ืฉื’ื“ืœ.
06:54
Compared to a rat, we might seem special, yes,
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ื‘ื”ืฉื•ื•ืื” ืœืขื›ื‘ืจ, ืื ื• ื ืจืื™ื ืžื™ื•ื—ื“ื™ื, ืื™ืŸ ืกืคืง,
06:57
but that's not a fair comparison to make,
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ืื‘ืœ ื–ื• ื”ืฉื•ื•ืื” ืœื ื”ื•ื’ื ืช,
06:59
given that we know that we are not rodents.
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ื‘ื”ื ื—ื” ืฉืื ื—ื ื• ื™ื•ื“ืขื™ื ืฉืื ื—ื ื• ืœื ืžื›ืจืกืžื™ื.
07:01
We are primates,
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ืื ื—ื ื• ืฉื™ื™ื›ื™ื ืœืžืฉืคื—ืช ื”ืงื•ืคืื™ื,
07:02
so the correct comparison is to other primates.
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ื›ืš ืฉื ื›ื•ืŸ ื™ื•ืชืจ ืœื”ืฉื•ื•ืช ืื•ืชื ื• ืœืงื•ืคืื™ื ืื—ืจื™ื.
07:05
And there, if you do the math,
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ื•ืื ื‘ื•ื“ืงื™ื ืฉื•ื‘ ืืช ื”ืžืฉื•ื•ืื”,
07:06
you find that a generic primate
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ืžื’ืœื™ื ืฉืœืงื•ืฃ ื›ืœืฉื”ื•
07:09
with 86 billion neurons
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ื‘ืขืœ 86 ืžื™ืœื™ืืจื“ ืชืื™ ืžื•ื—
07:11
would have a brain of about 1.2 kilos,
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ื™ื”ื™ื” ืžื•ื— ื‘ืžืฉืงืœ 1.2 ืง"ื’,
07:14
which seems just right,
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ื’ื•ื“ืœ ืฉื ืจืื” ืžืชืื™ื,
07:16
in a body of some 66 kilos,
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ืœื’ื•ืฃ ื‘ืžืฉืงืœ 66 ืง"ื’,
07:18
which in my case is exactly right,
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ืฉืžืชืื™ื ืœืžืฉืงืœ ืฉืœื™ ื‘ื“ื™ื•ืง,
07:21
which brings us to a very unsurprising
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ืžื” ืฉืžื•ื‘ื™ืœ ืื•ืชื ื• ืœืžืžืฆื ืœื ืžืคืชื™ืข
07:23
but still incredibly important conclusion:
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ืื‘ืœ ืขื“ื™ื™ืŸ ื—ืฉื•ื‘ ืžืื“:
07:26
I am a primate.
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ืื ื™ ืฉื™ื™ื›ืช ืœืžืฉืคื—ืช ื”ืงื•ืคืื™ื.
07:28
And all of you are primates.
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ื•ื’ื ืืชื ื›ื•ืœื›ื ืฉื™ื™ื›ื™ื ืœืžืฉืคื—ืช ื”ืงื•ืคืื™ื.
07:30
And so was Darwin.
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ื•ื’ื ืฆ'ืืจืœืก ื“ืืจื•ื™ืŸ.
07:32
I love to think that Darwin would have really appreciated this.
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ืื ื™ ืื•ื”ื‘ืช ืœื—ืฉื•ื‘ ืฉื“ืืจื•ื™ืŸ ื”ื™ื” ืžืขืจื™ืš ืืช ื”ืชื’ืœื™ืช ื”ื–ื•.
07:35
His brain, like ours,
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ื”ืžื•ื— ืฉืœื•, ื›ืžื• ืฉืœื ื•,
07:37
was made in the image of other primate brains.
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ื ื‘ื ื” ื‘ื“ืžื•ืชื ืฉืœ ืžื•ื—ื•ืช ืงื•ืคืื™ื ืื—ืจื™ื.
07:41
So the human brain may be remarkable, yes,
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ื›ืš ืฉื”ืžื•ื— ื”ืื ื•ืฉ ืื•ืœื™ ืžื“ื”ื™ื,
07:43
but it is not special in its number of neurons.
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ืื‘ืœ ื™ื™ื—ื•ื“ื• ืœื ื ื•ื‘ืข ืžืžืกืคืจ ืชืื™ ื”ืžื•ื—.
07:46
It is just a large primate brain.
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ื”ื•ื ืคืฉื•ื˜ ืžื•ื— ืฉืœ ืงื•ึนืคึธืื™ ื’ื“ื•ืœ.
07:48
I think that's a very humbling and sobering thought
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ืื ื™ ื—ื•ืฉื‘ืช ืฉืžื“ื•ื‘ืจ ื‘ืžื—ืฉื‘ื” ืฉืžืขื•ืจืจืช ืขื ื•ื•ื” ื•ื”ืชืคื›ื—ื•ืช
07:51
that should remind us of our place in nature.
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ืฉืฆืจื™ื›ื” ืœื”ื–ื›ื™ืจ ืœื ื• ืืช ืžืงื•ืžื ื• ื‘ื˜ื‘ืข.
07:54
Why does it cost so much energy, then?
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ืื‘ืœ ืœืžื” ื”ืžื•ื— ืฆื•ืจืš ื›ืœ ื›ืš ื”ืจื‘ื” ืื ืจื’ื™ื”?
07:56
Well, other people have figured out
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ื•ื‘ื›ืŸ, ืžื“ืขื ื™ื ืื—ืจื™ื ื—ื™ืฉื‘ื•
07:58
how much energy the human brain
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ื›ืžื” ืื ืจื’ื™ื” ืฆื•ืจืš ื”ืžื•ื— ื”ืื ื•ืฉื™
07:59
and that of other species costs,
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ื•ื›ืžื” ืฆื•ืจื›ื™ื ืžื•ื—ื•ืช ืฉืœ ืžื™ื ื™ื ืื—ืจื™ื,
08:01
and now that we knew how many neurons
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ื•ืขื›ืฉื™ื• ื›ืฉื™ื“ื•ืข ืœื ื• ืžืกืคืจ ืชืื™ ื”ืžื•ื—
08:02
each brain was made of, we could do the math.
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ืฉืžืจื›ื™ื‘ื™ื ื›ืœ ืžื•ื—, ื ื™ืชืŸ ืœื—ืฉื‘ ืืช ื”ืฆืจื™ื›ื”.
08:05
And it turns out that both human
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ืžืกืชื‘ืจ ืฉื”ืžื•ื— ื”ืื ื•ืฉื™
08:07
and other brains cost about the same,
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ื•ืžื•ื—ื•ืช ืฉืœ ื‘ืขืœื™ ื—ื™ื™ื ืื—ืจื™ื ืฆื•ืจื›ื™ื ื›ืžื•ืช ืื ืจื’ื™ื” ื“ื•ืžื”,
08:09
an average of six calories per billion neurons per day.
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ื‘ืขืจืš 6 ืงืœื•ืจื™ื•ืช ืœื™ืžืžื” ืœื›ืœ ืžื™ืœื™ืืจื“ ืชืื™ ืžื•ื—.
08:13
So the total energetic cost of a brain
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ื›ืš ืฉื”ืฆืจื™ื›ื” ื”ืื ืจื’ื˜ื™ืช ืฉืœ ื”ืžื•ื—
08:15
is a simple, linear function
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ื”ื™ื ืคืฉื•ื˜, ืคื•ื ืงืฆื™ื” ืœื™ื ื™ืืจื™ืช
08:17
of its number of neurons,
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ืฉืœ ืžืกืคืจ ืชืื™ ื”ืžื•ื—,
08:19
and it turns out that the human brain
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ื•ืžืกืชื‘ืจ ืฉื”ืžื•ื— ื”ืื ื•ืฉื™
08:21
costs just as much energy as you would expect.
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ืฆื•ืจืš ื›ืžื•ืช ืื ืจื’ื™ื” ื”ืชื•ืืžืช ื‘ื“ื™ื•ืง ืืช ื”ืžืฉื•ื•ืื”.
08:25
So the reason why the human brain
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ื›ืš ืฉื”ืกื™ื‘ื” ืฉื”ืžื•ื— ื”ืื ื•ืฉื™
08:27
costs so much energy is simply because
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ืฆื•ืจืš ื›ืœ ื›ืš ื”ืจื‘ื” ืื ืจื’ื™ื” ื”ื™ื ืคืฉื•ื˜ ื‘ื’ืœืœ
08:28
it has a huge number of neurons,
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ืฉื™ืฉ ื‘ื• ื”ืžื•ืŸ ืชืื™ ืžื•ื—,
08:30
and because we are primates
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ื•ื‘ื’ืœืœ ืฉืื ื—ื ื• ืฉื™ื™ื›ื™ื ืœืžืฉืคื—ืช ื”ืงื•ืคืื™ื
08:32
with many more neurons for a given body size
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ืขื ื›ืžื•ืช ื’ื“ื•ืœื” ืฉืœ ืชืื™ ืžื•ื— ื‘ื™ื—ืก ืœื’ื•ื“ืœ ื”ื’ื•ืฃ
08:34
than any other animal,
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ื‘ื”ืฉื•ื•ืื” ืœืžื™ื ื™ ื‘ืขืœื™ ื—ื™ื™ื ืื—ืจื™ื,
08:36
the relative cost of our brain is large,
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ื”ืžื—ื™ืจ ื”ื™ื—ืกื™ ืฉืœ ื”ืžื•ื— ืฉืœื ื• ื’ื“ื•ืœ,
08:39
but just because we're primates, not because we're special.
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ืื‘ืœ ืจืง ื‘ื’ืœืœ ืฉืื ื—ื ื• ืฉื™ื™ื›ื™ื ืœืžืฉืคื—ืช ื”ืงื•ืคืื™ื, ืœื ื‘ื’ืœืœ ืฉืื ื—ื ื• ืžื™ื•ื—ื“ื™ื.
08:42
Last question, then:
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ื•ืœืฉืืœื” ื”ืื—ืจื•ื ื”:
08:44
how did we come by this remarkable number of neurons,
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ืื™ืš ื”ื’ืขื ื• ืœืžืกืคืจ ืชืื™ ืžื•ื— ื’ื“ื•ืœ ื›ืœ ื›ืš,
08:47
and in particular, if great apes
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ื•ื‘ืขื™ืงืจ, ืื ื”ืงื•ืคื™ื ื”ื’ื“ื•ืœื™ื
08:49
are larger than we are,
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ื’ื“ื•ืœื™ื ืžืืชื ื•,
08:50
why don't they have a larger brain than we do, with more neurons?
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ืžื“ื•ืข ืื™ืŸ ืœื”ื ืžื•ื—ื•ืช ื’ื“ื•ืœื™ื ืžืฉืœื ื•, ืขื ื™ื•ืชืจ ืชืื™ ืžื•ื—?
08:54
When we realized how much expensive it is
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ื›ืฉืื ื—ื ื• ืžื—ืฉื‘ื™ื ื›ืžื” ืื ืจื’ื™ื” ืฆื•ืจืš
08:56
to have a lot of neurons in the brain, I figured,
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ืžื•ื— ื‘ืขืœ ื”ืจื‘ื” ืชืื™ ืžื•ื—, ืื ื™ ื—ื•ืฉื‘ืช,
08:58
maybe there's a simple reason.
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ืฉื™ืชื›ืŸ ื•ื”ืกื™ื‘ื” ืคืฉื•ื˜ื”.
09:00
They just can't afford the energy
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ืคืฉื•ื˜ ืื™ืŸ ืœื”ื ืžืกืคื™ืง ืื ืจื’ื™ื” ืœื‘ื–ื‘ื–
09:02
for both a large body and a large number of neurons.
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ืขืœ ื’ื•ืฃ ื’ื“ื•ืœ ื•ืžื•ื— ื’ื“ื•ืœ.
09:05
So we did the math.
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ืื– ื—ื™ืฉื‘ื ื• ืฉื•ื‘ ืืช ื”ื ืชื•ื ื™ื.
09:06
We calculated on the one hand
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ื—ื™ืฉื‘ื ื• ืžืฆื“ ืื—ื“
09:08
how much energy a primate gets per day
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ื›ืžื” ืื ืจื’ื™ื” ืฆื•ืจื›ื™ื ืงื•ืคืื™ื ื‘ื™ืžืžื”
09:10
from eating raw foods,
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ืžืื›ื™ืœืช ืžื–ื•ืŸ ื ื,
09:11
and on the other hand, how much energy
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ื•ืžืฆื“ ืฉื ื™, ื›ืžื” ืื ืจื’ื™ื”
09:13
a body of a certain size costs
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ืฆื•ืจืš ื’ื•ืฃ ื‘ืžื™ื“ื” ืžืกื•ื™ื™ืžืช
09:15
and how much energy a brain of a certain number of neurons costs,
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ื•ื›ืžื” ืื ืจื’ื™ื” ืฆื•ืจืš ืžื•ื— ื‘ืขืœ ืžืกืคืจ ืžืกื•ื™ื ืฉืœ ืชืื™ ืžื•ื—,
09:19
and we looked for the combinations
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ื•ื”ื‘ื˜ื ื• ื‘ืฉื™ืœื•ื‘ื™ื ื”ืฉื•ื ื™ื
09:20
of body size and number of brain neurons
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ืฉืœ ื’ื•ื“ืœ ื’ื•ืฃ ื•ืžืกืคืจ ืชืื™ ืžื•ื—
09:22
that a primate could afford
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ืฉืžืชืื™ืžื™ื ืœืฆืจื™ื›ืช ื”ืื ืจื’ื™ื” ืฉืœ ืงื•ืคืื™ื
09:24
if it ate a certain number of hours per day.
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ืฉืื•ื›ืœื™ื ื‘ืžืฉืš ืžืกืคืจ ืฉืขื•ืช ื ืชื•ืŸ ื‘ื™ืžืžื”.
09:26
And what we found is that
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ื•ืžื” ืฉื’ื™ืœื™ื ื• ื”ื•ื
09:28
because neurons are so expensive,
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ืฉื‘ื’ืœืœ ืฉืชืื™ ื”ืžื•ื— ืฆื•ืจื›ื™ื ื›ืœ ื›ืš ื”ืจื‘ื” ืื ืจื’ื™ื”,
09:30
there is a tradeoff between body size and number of neurons.
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ื™ืฉ ื™ื—ืก ื”ืคื•ืš ื‘ื™ืŸ ื’ื•ื“ืœ ื”ื’ื•ืฃ ื•ืžืกืคืจ ืชืื™ ื”ืžื•ื—.
09:33
So a primate that eats eight hours per day
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ื›ืš ืฉืงื•ืฃ ืฉืื•ื›ืœ ื‘ืžืฉืš 8 ืฉืขื•ืช ื‘ื™ืžืžื”
09:36
can afford at most 53 billion neurons,
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ื™ื›ื•ืœ ืœื”ืจืฉื•ืช ืœืขืฆืžื• ืžื•ื— ืขื 53 ืžื™ืœื™ืืจื“ ืชืื™ ืžื•ื—,
09:39
but then its body cannot be any bigger
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ืื‘ืœ ื”ืžืฆื‘ ื›ื–ื” ื’ื•ืคื• ืœื ื™ื›ื•ืœ ืœื”ื™ื•ืช ื›ื‘ื“
09:41
than 25 kilos.
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ืž- 25 ืง"ื’.
09:43
To weigh any more than that,
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ืขืœ ืžื ืช ืœืฉืงื•ืœ ื™ื•ืชืจ ืžื›ืš,
09:45
it has to give up neurons.
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ื”ื•ื ื—ื™ื™ื‘ ืœื•ื•ืชืจ ืขืœ ืชืื™ ืžื•ื—.
09:46
So it's either a large body
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ืฆืจื™ืš ืœื‘ื—ื•ืจ ื‘ื™ืŸ ื’ื•ืฃ ื’ื“ื•ืœ
09:49
or a large number of neurons.
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ืื• ืžืกืคืจ ื’ื“ื•ืœ ืฉืœ ืชืื™ ืžื•ื—.
09:50
When you eat like a primate,
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ื›ืฉืืชื” ืื•ื›ืœ ื›ืžื• ืงื•ืฃ ืงื•ืคืื™,
09:52
you can't afford both.
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ืืชื” ืœื ื™ื›ื•ืœ ืœืงื‘ืœ ืืช ืฉื ื™ื”ื.
09:54
One way out of this metabolic limitation
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ื“ืจืš ืื—ืช ืœืขืงื•ืฃ ืืช ื”ืžื’ื‘ืœื” ื”ืžื˜ื‘ื•ืœื™ืช
09:56
would be to spend even more hours per day eating,
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ื”ื™ื ืœืื›ื•ืœ ื‘ืžืฉืš ื™ื•ืชืจ ืฉืขื•ืช ื‘ื™ื•ื,
09:59
but that gets dangerous,
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ืื‘ืœ ืžื“ื•ื‘ืจ ื‘ืฆืขื“ ืžืกื•ื›ืŸ,
10:01
and past a certain point, it's just not possible.
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ื•ืžืขื‘ืจ ืœื ืงื•ื“ื” ืžืกื•ื™ืžืช, ื–ื” ืคืฉื•ื˜ ื‘ืœืชื™ ืืคืฉืจื™.
10:04
Gorillas and orangutans, for instance,
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ื’ื•ืจื™ืœื•ืช ื•ืื•ืจื ื’ื•ื˜ื ื™ื, ืœื“ื•ื’ืžื”,
10:05
afford about 30 billion neurons
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ืžืฉืชืžืฉื™ื ื‘- 30 ืžื™ืœื™ืืจื“ ืชืื™ ืžื•ื—
10:07
by spending eight and a half hours per day eating,
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ื›ืฉื”ื ืžื‘ืœื™ื 8.5 ืฉืขื•ืช ื‘ื™ื•ื ื‘ืื›ื™ืœื”,
10:10
and that seems to be about as much as they can do.
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ื•ื ืจืื” ืฉื”ื ืœื ืžืกื•ื’ืœื™ื ืœื‘ืœื•ืช ื™ื•ืชืจ ื–ืžืŸ ื‘ื—ื™ืคื•ืฉ ืžื–ื•ืŸ.
10:13
Nine hours of feeding per day
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9 ืฉืขื•ืช ืื›ื™ืœื” ื‘ื™ืžืžื”
10:15
seems to be the practical limit for a primate.
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ืžื”ื•ื•ื™ื ืืช ื”ืžื’ื‘ืœื” ื”ืžืขืฉื™ืช ืฉืœ ื”ืงื•ืคืื™ื.
10:18
What about us?
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ื•ืžื” ืื™ืชื ื•?
10:20
With our 86 billion neurons
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ืขื 86 ืžื™ืœื™ืืจื“ ืชืื™ ืžื•ื—
10:21
and 60 to 70 kilos of body mass,
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ื•ื’ื•ืฃ ื‘ืžืฉืงืœ 60 ืขื“ 70 ืง"ื’
10:25
we should have to spend over nine hours
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ืื ื—ื ื• ื”ื™ื™ื ื• ืฆืจื™ื›ื™ื ืœื‘ืœื•ืช ื™ื•ืชืจ ืž- 9 ืฉืขื•ืช
10:28
per day every single day feeding,
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ื‘ื›ืœ ื™ื•ื ื‘ืื›ื™ืœื”,
10:32
which is just not feasible.
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ื•ื–ื” ืคืฉื•ื˜ ืœื ืืคืฉืจื™.
10:34
If we ate like a primate,
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ืื ื”ื™ื™ื ื• ืื•ื›ืœื™ื ื›ืžื• ืงื•ืคืื™ื,
10:36
we should not be here.
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ืœื ื”ื™ื™ื ื• ืžืชืงื™ื™ืžื™ื.
10:38
How did we get here, then?
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ืื– ืื™ืš ื”ื’ืขื ื• ืœื›ืืŸ?
10:40
Well, if our brain costs just as much energy
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ื•ื‘ื›ืŸ, ื”ืžื•ื— ืฉืœื ื• ืฆื•ืจืš ืืช ื›ืœ ื”ืื ืจื’ื™ื”
10:43
as it should, and if we can't spend
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ืฉื”ื•ื ืฆืจื™ืš, ื•ืžื›ื™ื•ื•ืŸ ืฉืœื ื ื™ืชืŸ
10:44
every waking hour of the day feeding,
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ืœื‘ื–ื‘ื– ืืช ื›ืœ ืฉืขื•ืช ื”ืขืจื•ืช ื‘ืื›ื™ืœื”,
10:48
then the only alternative, really,
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ื”ื—ืœื•ืคื” ื”ื™ื—ื™ื“ื”, ื”ืืžืชื™ืช,
10:50
is to somehow get more energy
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ื”ื™ื ืœื”ืฉื™ื’ ื‘ื“ืจืš ื›ืœืฉื”ื™ ื™ื•ืชืจ ืื ืจื’ื™ื”
10:52
out of the same foods.
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ืžืื•ืชื” ื›ืžื•ืช ืฉืœ ืžื–ื•ืŸ.
10:54
And remarkably, that matches exactly
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ื•ื‘ืื•ืคืŸ ืžืคืœื™ื, ื–ื” ืชื•ืื ื‘ืื•ืคืŸ ืžื“ื•ื™ืง
10:58
what our ancestors are believed to have invented
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ืœื”ืžืฆืื” ืฉื”ืžืฆื™ืื• ื›ื›ืœ ื”ื ืจืื” ืื‘ื•ืชื™ื ื•
11:01
one and a half million years ago,
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ืœืคื ื™ ืžื™ืœื™ื•ืŸ ื•ื—ืฆื™ ืฉื ื™ื,
11:03
when they invented cooking.
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ื›ืฉื”ื ื”ืžืฆื™ืื• ืืช ื”ื‘ื™ืฉื•ืœ.
11:05
To cook is to use fire
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ื”ื‘ื™ืฉื•ืœ ืžืฉืชืžืฉ ื‘ืืฉ
11:07
to pre-digest foods outside of your body.
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ืขืœ ืžื ืช ืœื‘ืฆืข ืคืจื•ืง ืจืืฉื•ื ื™ ืฉืœ ื”ืžื–ื•ืŸ ืžื—ื•ืฅ ืœื’ื•ืฃ.
11:11
Cooked foods are softer, so they're easier to chew
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ืžื–ื•ืŸ ืžื‘ื•ืฉืœ ื”ื•ื ืจืš ื™ื•ืชืจ, ื•ืงืœ ื™ื•ืชืจ ืœืœืขื•ืก ืื•ืชื•
11:14
and to turn completely into mush in your mouth,
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ื•ืœื”ืคื•ืš ืื•ืชื• ื‘ืคื” ืœืขื™ืกื”,
11:16
so that allows them to be completely digested
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ื•ื›ืš ื ื™ืชืŸ ืœืขื›ืœ ืืช ื”ืžื–ื•ืŸ ื‘ืžืœื•ืื•
11:18
and absorbed in your gut,
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ื•ืœืกืคื•ื’ ืื•ืชื• ื‘ืžืขื™ื™ื,
11:20
which makes them yield much more energy in much less time.
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ื•ื›ืš ืœื ืฆืœ ื”ืจื‘ื” ื™ื•ืชืจ ืื ืจื’ื™ื” ื‘ื”ืจื‘ื” ืคื—ื•ืช ื–ืžืŸ.
11:24
So cooking frees time for us to do
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ื›ืš ืฉื”ื‘ื™ืฉื•ืœ ืคื™ื ื” ืขื‘ื•ืจื ื• ื–ืžืŸ ืขืœ ืžื ืช
11:26
much more interesting things with our day
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ืฉื ื•ื›ืœ ืœืขืฉื•ืช ื“ื‘ืจื™ื ืžืขื ื™ื™ื ื™ื ื™ื•ืชืจ ื‘ืžื”ืœืš ื”ื™ื•ื
11:28
and with our neurons
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ื•ืขื ื›ืžื•ืช ืชืื™ ื”ืžื•ื— ืฉืœื ื•
11:30
than just thinking about food,
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ืžืืฉืจ ืจืง ืœื—ืฉื•ื‘ ืขืœ ืื•ื›ืœ,
11:31
looking for food, and gobbling down food
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ืœื—ืคืฉ ืื•ื›ืœ, ื•ืœื–ืœื•ืœ ืื•ื›ืœ
11:33
all day long.
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ื‘ืžืฉืš ื›ืœ ื”ื™ื•ื.
11:34
So because of cooking, what once was
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ื›ืš ืฉื‘ื–ื›ื•ืช ื”ื‘ื™ืฉื•ืœ, ืžื” ืฉืคืขื ื”ื™ื”
11:37
a major liability, this large,
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ืžื˜ืœื” ืขื™ืงืจื™ืช, ื”ืžื•ื— ื”ื’ื“ื•ืœ
11:39
dangerously expensive brain with a lot of neurons,
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ื•ื”ื™ืงืจ ืœื”ื—ืจื™ื“ ืฉืœื ื•, ื‘ืขืœ ืชืื™ ื”ืžื•ื— ื”ืจื‘ื™ื,
11:42
could now become a major asset,
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ื”ืคืš ืœื”ื™ื•ืช ืœื ื›ืก ืขื™ืงืจื™,
11:44
now that we could both afford the energy for a lot of neurons
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ืขื›ืฉื™ื• ื›ืฉื”ื™ื™ืชื” ืœื ื• ืžืกืคื™ืง ืื ืจื’ื™ื” ื’ื ืขื‘ื•ืจ ืชืื™ ื”ืžื•ื—
11:48
and the time to do interesting things with them.
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ื•ื’ื ืขื‘ื•ืจ ื–ืžืŸ ืคื ื•ื™ ืขืœ ืžื ืช ืœื”ืฉืชืžืฉ ื‘ื”ื ืœื“ื‘ืจื™ื ืžืขื ื™ื™ื ื™ื.
11:50
So I think this explains why the human brain
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ื ืจืื” ืœื™ ืฉื–ื” ืžืกื‘ื™ืจ ืœืžื” ื”ืžื•ื— ื”ืื ื•ืฉื™
11:52
grew to become so large so fast in evolution,
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ื’ื“ืœ ืœืžืžื“ื™ื ื›ื” ื’ื“ื•ืœื™ื ื›ืœ ื›ืš ืžื”ืจ ื‘ืื‘ื•ืœื•ืฆื™ื”,
11:55
all of the while remaining just a primate brain.
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ื‘ื–ืžืŸ ืฉื‘ื‘ืกื™ืกื• ื”ื•ื ืจืง ืžื•ื— ืฉืœ ืงื•ืคืื™.
11:59
With this large brain now affordable by cooking,
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ื‘ืฉืœื‘ ื‘ื• ื”ื‘ื™ืฉื•ืœ ืื™ืคืฉืจ ืœืงื™ื™ื ืžื•ื— ื’ื“ื•ืœ
12:02
we went rapidly from raw foods to culture,
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ื”ืชืงื“ืžื ื• ื‘ืžื”ื™ืจื•ืช ืžืชืจื‘ื•ืช ืฉืฆื•ืจื›ืช ืžื–ื•ืŸ ื ื,
12:05
agriculture, civilization, grocery stores,
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ืœื—ืงืœืื•ืช, ืฆื™ื‘ื™ืœื™ื–ืฆื™ื”, ื—ื ื•ื™ื•ืช ืžื›ื•ืœืช,
12:07
electricity, refrigerators,
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ื—ืฉืžืœ, ืžืงืจืจื™ื,
12:09
all of those things that nowadays
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ื•ื›ืœ ื”ื“ื‘ืจื™ื ืฉื›ื™ื•ื
12:11
allow us to get all the energy we need
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ืžืืคืฉืจื™ื ืœื ื• ืœื”ืฉื™ื’ ืืช ื›ืœ ื”ืื ืจื’ื™ื” ื”ื“ืจื•ืฉื” ืœื ื•
12:13
for the whole day in a single sitting
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ืœื™ื•ื ืฉืœื ื‘ืืจื•ื—ื” ืื—ืช
12:16
at your favorite fast food joint.
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ื‘ืžืกืขื“ืช ื”ืžื–ื•ืŸ ื”ืžื”ื™ืจ ื”ื—ื‘ื™ื‘ื” ืขืœื™ื ื•.
12:18
So what once was a solution
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ื›ืš ืฉืžื” ืฉื”ื™ื” ืคืขื ืคืชืจื•ืŸ
12:21
now became the problem,
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ื”ื•ืคืš ื›ื™ื•ื ืœื‘ืขื™ื”,
12:23
and ironically, we look for the solution in raw food.
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ื•ื‘ืื•ืคืŸ ืื™ืจื•ื ื™, ืื ื—ื ื• ืžื—ืคืฉื™ื ืืช ื”ืคืชืจื•ืŸ ื‘ืžื–ื•ืŸ ื”ื ื.
12:28
So what is the human advantage?
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ืื– ืžื”ื• ื”ื™ืชืจื•ืŸ ื”ืื ื•ืฉื™?
12:31
What is it that we have
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ืžื” ื™ืฉ ืœื ื•
12:32
that no other animal has?
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ืฉืื™ืŸ ืœื‘ืขืœื™ ื”ื—ื™ื™ื ื”ืื—ืจื™ื?
12:35
My answer is that we have the largest number
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ื”ืชืฉื•ื‘ื” ืฉืœื™ ื”ื™ื ืฉื™ืฉ ืœื ื• ืืช ื”ืžืกืคืจ ื”ื’ื“ื•ืœ ื‘ื™ื•ืชืจ
12:37
of neurons in the cerebral cortex,
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ืฉืœ ืชืื™ ืžื•ื— ื‘ืงืœื™ืคืช ื”ืžื•ื—,
12:39
and I think that's the simplest explanation
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ื•ืื ื™ ื—ื•ืฉื‘ืช ืฉื–ื”ื• ื”ื”ืกื‘ืจ ื”ืคืฉื•ื˜ ื‘ื™ื•ืชืจ
12:40
for our remarkable cognitive abilities.
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ืœื™ื›ื•ืœื•ืช ื”ืฉื›ืœื™ื•ืช ื”ืžื•ืคืœืื•ืช ืฉืœื ื•.
12:42
And what is it that we do that no other animal does,
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ื•ืžื” ืื ื—ื ื• ืขื•ืฉื™ื ืฉืžื‘ื“ืœ ืื•ืชื ื• ืžื‘ืขืœื™ ื”ื—ื™ื™ื,
12:46
and which I believe was fundamental
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ื•ืฉืœื“ืขืชื™ ื”ื•ื ื”ื‘ืกื™ืก
12:48
to allow us to reach that large,
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ืœื™ื›ื•ืœืชื ื• ืœื”ื’ื™ืข
12:51
largest number of neurons in the cortex?
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ืœืžืกืคืจ ื”ืขืฆื•ื ืฉืœ ืชืื™ ืžื•ื— ื‘ืงืœื™ืคืช ื”ืžื•ื—?
12:53
In two words, we cook.
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ื‘ืฉืชื™ ืžืœื™ื, ืื ื—ื ื• ืžื‘ืฉืœื™ื.
12:55
No other animal cooks its food. Only humans do.
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ืืฃ ื—ื™ื” ืื—ืจืช ืœื ืžื‘ืฉืœืช ืืช ืžื–ื•ื ื”. ืจืง ื‘ื ื™ ื”ืื“ื.
12:59
And I think that's how we got to become human.
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ื•ืื ื™ ื—ื•ืฉื‘ืช ืฉื–ื” ืžื” ืฉื”ืคืš ืื•ืชื ื• ืœื‘ื ื™ ืื“ื.
13:02
Studying the human brain changed the way I think about food.
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ืœื™ืžื•ื“ ื”ืžื•ื— ื”ืื ื•ืฉื™ ืฉื™ื ื” ืืช ื”ื“ืจืš ื‘ื” ืื ื™ ื—ื•ืฉื‘ืช ืขืœ ืžื–ื•ืŸ.
13:04
I now look at my kitchen,
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ื›ื™ื•ื ืื ื™ ืžืกืชื›ืœืช ืขืœ ื”ืžื˜ื‘ื— ืฉืœื™,
13:06
and I bow to it,
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ื•ืื ื™ ืžืฉืชื—ื•ื•ื” ืœื•,
13:07
and I thank my ancestors for coming up
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ื•ืื ื™ ืžื•ื“ื” ืœืื‘ื•ืชื™ื™ ื”ืงื“ืžื•ื ื™ื ืฉื”ืžืฆื™ืื•
13:09
with the invention that probably made us humans.
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ืืช ื”ื”ืžืฆืื” ืฉื”ืคื›ื” ืื•ืชื ื• ืœืื ื•ืฉื™ื.
13:11
Thank you very much.
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ืชื•ื“ื” ืจื‘ื” ืœื›ื.
13:13
(Applause)
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(ืžื—ื™ืื•ืช ื›ืคื™ื™ื)
ืขืœ ืืชืจ ื–ื”

ืืชืจ ื–ื” ื™ืฆื™ื’ ื‘ืคื ื™ื›ื ืกืจื˜ื•ื ื™ YouTube ื”ืžื•ืขื™ืœื™ื ืœืœื™ืžื•ื“ ืื ื’ืœื™ืช. ืชื•ื›ืœื• ืœืจืื•ืช ืฉื™ืขื•ืจื™ ืื ื’ืœื™ืช ื”ืžื•ืขื‘ืจื™ื ืขืœ ื™ื“ื™ ืžื•ืจื™ื ืžื”ืฉื•ืจื” ื”ืจืืฉื•ื ื” ืžืจื—ื‘ื™ ื”ืขื•ืœื. ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ื”ืžื•ืฆื’ื•ืช ื‘ื›ืœ ื“ืฃ ื•ื™ื“ืื• ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ ืžืฉื. ื”ื›ืชื•ื‘ื™ื•ืช ื’ื•ืœืœื•ืช ื‘ืกื ื›ืจื•ืŸ ืขื ื”ืคืขืœืช ื”ื•ื•ื™ื“ืื•. ืื ื™ืฉ ืœืš ื”ืขืจื•ืช ืื• ื‘ืงืฉื•ืช, ืื ื ืฆื•ืจ ืื™ืชื ื• ืงืฉืจ ื‘ืืžืฆืขื•ืช ื˜ื•ืคืก ื™ืฆื™ืจืช ืงืฉืจ ื–ื”.

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