TEDGlobal 2013
Suzana Herculano-Houzel: What is so special about the human brain?
Zakaj so človeški možgani tako posebni?
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Človeški možgani so uganka - glede na velikost naših teles so absurdno veliki, za svojo velikost porabijo gromozanske količine energije in imajo nenavadno gosto možgansko skorjo. Toda zakaj? Nevroznanstvenica Suzana Herculano-Houzel si nadane detektivski klobuk in nas vodi skozi to uganko. Z izdelavo "možganske juhe" nas privede do presenetljivih zaključkov.
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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Zakaj so človeški možgani tako posebni?
00:15
Why is it that we study other animals
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Zakaj mi proučujemo druge živali
00:17
instead of them studying us?
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in ne one nas?
00:19
What does a human brain have or do
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Kaj imajo človeški možgani,
00:21
that no other brain does?
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česar nimajo nobeni drugi?
00:23
When I became interested
in these questions about 10 years ago,
in these questions about 10 years ago,
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Pred desetimi leti sem se
začela zanimati za ta vprašanja,
začela zanimati za ta vprašanja,
00:26
scientists thought they knew
what different brains were made of.
what different brains were made of.
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in znanstveniki so mislili, da vedo,
kako so možgani sestavljeni.
kako so možgani sestavljeni.
00:28
Though it was based on very little evidence,
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Kljub malo dokazom,
00:30
many scientists thought that all mammalian brains,
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so mnogi mislili,
da so možgani vseh sesalcev,
da so možgani vseh sesalcev,
00:32
including the human brain,
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vključno s človeškimi,
00:34
were made in the same way,
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sestavljeni na enak način,
00:35
with a number of neurons that was always
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s številom nevronov, ki je vedno
00:37
proportional to the size of the brain.
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v sorazmerju z velikostjo možganov.
00:39
This means that two brains of the same size,
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To pomeni, da bi dvoje enakih možganov
00:41
like these two, with a respectable 400 grams,
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tako kot ti, ki tehtajo 400 gramov,
00:45
should have similar numbers of neurons.
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morali imeti podobno število nevronov.
00:47
Now, if neurons are the functional
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Torej, če so nevroni
funkcionalne enote možganov,
funkcionalne enote možganov,
00:49
information processing units of the brain,
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ki obdelujejo informacije,
00:52
then the owners of these two brains
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bi morala imeti lastnika teh možganov
00:54
should have similar cognitive abilities.
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podobne kognitivne zmožnosti.
00:56
And yet, one is a chimp,
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Toda en je šimpanz,
00:59
and the other is a cow.
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drugi pa krava.
01:01
Now maybe cows have a really rich
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No, mogoče imajo krave
zelo živahno miselno življenje
in so tako pametne,
in so tako pametne,
01:04
internal mental life and are so smart
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01:06
that they choose not to let us realize it,
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da to pred nami skrivajo,
01:10
but we eat them.
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toda jemo jih.
01:11
I think most people will agree
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Mislim, da se bo večina strinjala,
01:13
that chimps are capable of much more complex,
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da so šimpanzi zmožni
dosti bolj zapletenega,
dosti bolj zapletenega,
01:15
elaborate and flexible behaviors than cows are.
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izpiljenega in prilagodljivega
obnašanja kot krave.
obnašanja kot krave.
01:18
So this is a first indication that the
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To je torej prvi kazalec, da trditev
01:20
"all brains are made the same way" scenario
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"vsi možgani so sestavljeni enako"
01:22
is not quite right.
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ni čisto pravilna.
01:24
But let's play along.
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Ampak vseeno se poigrajmo z njo.
01:25
If all brains were made the same way
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Če bi bili vsi možgani enaki
01:27
and you were to compare animals
with brains of different sizes,
with brains of different sizes,
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in mi bi primerjali živali
z možgani različnih velikosti,
z možgani različnih velikosti,
01:30
larger brains should always have more neurons
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bi večji možgani
vedno morali imeti več nevronov
vedno morali imeti več nevronov
01:32
than smaller brains,
and the larger the brain,
and the larger the brain,
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kot manjši možgani
in večji kot bi možgani bili,
in večji kot bi možgani bili,
01:34
the more cognitively able its owner should be.
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bolj kognitivno sposoben
bi moral biti njihov lastnik.
bi moral biti njihov lastnik.
01:37
So the largest brain around should also be
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Torej bi morali biti največji možgani
01:39
the most cognitively able.
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tudi najbolj sposobni.
01:42
And here comes the bad news:
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Toda tu je slaba novica:
01:43
Our brain, not the largest one around.
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Naši možgani niso največji naokrog.
01:46
It seems quite vexing.
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V bistvu je kar razburljivo.
01:47
Our brain weighs between 1.2 and 1.5 kilos,
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Naši možgani tehtajo
med 1,2 in 1,5 kilograma,
med 1,2 in 1,5 kilograma,
01:50
but elephant brains weigh between four and five kilos,
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slonovi možgani med 4 in 5 kilogrami
01:54
and whale brains can weigh up to nine kilos,
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in kitovi možgani tudi do 9 kilogramov,
01:56
which is why scientists used to resort to saying
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zato so se znanstveniki
zatekali k trditvi,
zatekali k trditvi,
02:01
that our brain must be special
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da so naši možgani nekaj posebnega.
02:03
to explain our cognitive abilities.
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Tako so lahko razložili
naše kognitivne zmožnosti.
naše kognitivne zmožnosti.
02:06
It must be really extraordinary,
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Naši možgani morajo biti
res nekaj izrednega,
res nekaj izrednega,
02:09
an exception to the rule.
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neka izjema k pravilu.
02:11
Theirs may be bigger, but ours is better,
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Njihovi možgani so morda večji,
toda naši so boljši
toda naši so boljši
02:14
and it could be better, for example,
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in bi bili boljši na primer v tem,
02:16
in that it seems larger than it should be,
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da se zdijo večji kot bi morali biti,
02:18
with a much larger cerebral cortex
than we should have
than we should have
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z dosti večjo površino
možganske skorje kot pričakovano
možganske skorje kot pričakovano
02:21
for the size of our bodies.
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glede na velikost našega telesa.
02:22
So that would give us extra cortex
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Tako bi imeli več skorje,
da bi lahko počeli bolj zanimive stvari
kot pa le upravljali telo.
kot pa le upravljali telo.
02:24
to do more interesting things
than just operating the body.
than just operating the body.
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02:27
That's because the size of the brain
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To je zato, ker velikost možganov
02:29
usually follows the size of the body.
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navadno sledi velikosti telesa.
02:31
So the main reason for saying that
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Glavni razlog za trditev,
02:33
our brain is larger than it should be
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da so naši možgani večji kot bi morali biti,
02:35
actually comes from comparing ourselves
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v bistvu izhaja iz primerjave ljudi
02:37
to great apes.
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z velikimi opicami.
02:39
Gorillas can be two to three times larger than we are,
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Gorile so lahko
tudi do trikrat večje od nas,
tudi do trikrat večje od nas,
02:41
so their brains should also be larger than ours,
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torej bi njihovi možgani
morali biti večji kot naši,
morali biti večji kot naši,
02:44
but instead it's the other way around.
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v bistvu pa je ravno nasprotno.
02:46
Our brain is three times larger than a gorilla brain.
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Naši možgani
so trikrat večji od gorilinih.
so trikrat večji od gorilinih.
02:49
The human brain also seems special
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Človeški možgani so tudi posebni,
02:51
in the amount of energy that it uses.
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kar se tiče porabe energije.
02:53
Although it weighs only two percent of the body,
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Čeprav možgani tehtajo
le dva odstotka telesa,
le dva odstotka telesa,
02:56
it alone uses 25 percent of all the energy
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porabijo 25 odstotkov celotne energije,
02:59
that your body requires to run per day.
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ki jo naše telo na dan potrebuje.
03:02
That's 500 calories out of a total of 2,000 calories,
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To pomeni 500 od skupaj 2.000 kalorij
03:05
just to keep your brain working.
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samo za delovanje naših možganov.
03:07
So the human brain is larger than it should be,
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Človeški možgani so večji,
kot bi morali biti,
kot bi morali biti,
03:10
it uses much more energy than it should,
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porabijo več energije, kot bi jo morali,
03:12
so it's special.
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torej so posebni.
03:14
And this is where the story started to bother me.
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Tu pa me je nekaj zmotilo.
03:16
In biology, we look for rules
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V biologiji iščemo pravila,
03:18
that apply to all animals and to life in general,
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ki se nanašajo
na živali in življenje na splošno,
na živali in življenje na splošno,
03:21
so why should the rules of evolution
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zakaj bi torej morala pravila evolucije
03:23
apply to everybody else but not to us?
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veljati za vse, le za nas ne?
03:26
Maybe the problem was with the basic assumption
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Mogoče je problem v tem,
da je osnovna trditev,
da je osnovna trditev,
03:29
that all brains are made in the same way.
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da so vsi možgani sestavljeni enako.
03:30
Maybe two brains of a similar size
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Morda so dvoji podobno težki možgani
03:32
can actually be made of
very different numbers of neurons.
very different numbers of neurons.
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sestavljeni iz zelo različnega
števila nevronov.
števila nevronov.
03:35
Maybe a very large brain
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Morda veliki možgani
03:36
does not necessarily have more neurons
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nimajo nujno več nevronov
03:38
than a more modest-sized brain.
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kot možgani bolj skromne velikosti.
03:40
Maybe the human brain
actually has the most neurons
actually has the most neurons
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Mogoče imajo človeški možgani
največ nevronov
največ nevronov
03:43
of any brain, regardless of its size,
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od vseh možganov,
ne glede na njihovo velikost,
ne glede na njihovo velikost,
03:46
especially in the cerebral cortex.
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še posebej v možganski skorji.
03:48
So this to me became
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Zame je to postalo
03:50
the important question to answer:
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najpomembnejše vprašanje:
03:51
how many neurons does the human brain have,
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Koliko nevronov imajo človeški možgani
03:54
and how does that compare to other animals?
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in kako je to število
primerljivo z drugimi živalmi?
primerljivo z drugimi živalmi?
03:56
Now, you may have heard or read somewhere
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Mogoče ste kje že slišali ali prebrali,
03:59
that we have 100 billion neurons,
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da imamo 100 milijard nevronov,
zato sem pred desetimi leti
svoje kolege vprašala,
svoje kolege vprašala,
04:01
so 10 years ago, I asked my colleagues
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04:03
if they knew where this number came from.
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ali vedo, od kod izhaja to število.
04:05
But nobody did.
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A nihče ni vedel.
04:06
I've been digging through the literature
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Brskala sem po literaturi,
04:08
for the original reference for that number,
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da bi našla izvirno omembo tega števila,
04:10
and I could never find it.
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a je nikoli nisem našla.
04:11
It seems that nobody had actually ever counted
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Zdi se, da v bistvu še nihče ni štel
nevronov v človeških možganih,
04:14
the number of neurons in the human brain,
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04:16
or in any other brain for that matter.
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pravzaprav še v nobenih možganih.
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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Zato sem iznašla
svoj način štetja celic v možganih,
svoj način štetja celic v možganih,
04:22
and it essentially consists of
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in sicer možgane raztapljam v juho.
04:24
dissolving that brain into soup.
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04:27
It works like this:
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Tako deluje:
04:29
You take a brain, or parts of that brain,
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Vzamemo možgane ali dele možganov
04:32
and you dissolve it in detergent,
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in jih raztopimo v detergentu,
04:34
which destroys the cell membranes
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ki uniči celično membrano,
04:35
but keeps the cell nuclei intact,
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jedro pa pusti nedotaknjeno,
04:38
so you end up with a suspension of free nuclei
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tako da dobimo suspenzijo prostih jeder,
04:41
that looks like this,
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ki izgleda takole -
04:43
like a clear soup.
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kot bistra juha.
04:44
This soup contains all the nuclei
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Juha vsebuje vsa jedra,
04:46
that once were a mouse brain.
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ki so nekoč bila mišji možgani.
04:48
Now, the beauty of a soup is that because it is soup,
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No, prednost juhe je,
da jo lahko premešamo
da jo lahko premešamo
04:51
you can agitate it and make those nuclei
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in vsa jedra se homogeno
04:54
be distributed homogeneously in the liquid,
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razporedijo v tekočini,
04:56
so that now by looking under the microscope
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zato da lahko zdaj pod mikroskopom
04:58
at just four or five samples
of this homogeneous solution,
of this homogeneous solution,
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v le štirih ali petih vzorcih
te homogene raztopine
te homogene raztopine
05:02
you can count nuclei, and therefore tell
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preštejemo jedra
in tako vemo,
koliko celic so imeli ti možgani.
koliko celic so imeli ti možgani.
05:05
how many cells that brain had.
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05:06
It's simple, it's straightforward,
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To je preprost
05:08
and it's really fast.
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in tudi hiter postopek.
05:09
So we've used that method to count neurons
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To metodo smo uporabili za štetje nevronov
05:11
in dozens of different species so far,
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pri ducatih različnih vrst do sedaj.
05:14
and it turns out that all brains
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Izkazalo se je, da vsi možgani
05:15
are not made the same way.
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niso sestavljeni enako.
05:18
Take rodents and primates, for instance:
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Vzemimo na primer glodavce in primate:
05:20
In larger rodent brains, the average size
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V večjih možganih glodavcev
se povprečna velikost nevronov povečuje,
05:22
of the neuron increases,
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05:24
so the brain inflates very rapidly
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zato se možgani hitro napihnejo
05:27
and gains size much faster than it gains neurons.
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in pridobijo na velikosti dosti hitreje
kot na nevronih.
kot na nevronih.
05:30
But primate brains gain neurons
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Primati pa dobijo nevrone
05:32
without the average neuron becoming any larger,
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ne da bi se povprečni nevroni povečali,
05:34
which is a very economical way
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kar je zelo ekonomičen način
05:35
to add neurons to your brain.
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dodajanja nevronov k možganom.
Rezultat tega je,
da imajo možgani primatov
da imajo možgani primatov
05:37
The result is that a primate brain
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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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več nevronov
kot možgani glodavcev iste velikosti
kot možgani glodavcev iste velikosti
05:42
and the larger the brain,
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in večji kot so možgani,
05:44
the larger this difference will be.
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večja bo razlika.
05:46
Well, what about our brain then?
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Kako je torej z našimi možgani?
05:48
We found that we have, on average,
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Odkrili smo, da imamo v povprečju
05:50
86 billion neurons,
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86 milijard nevronov,
05:51
16 billion of which are in the cerebral cortex,
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od katerih je 16 milijard
v možganski skorji.
v možganski skorji.
05:54
and if you consider that the cerebral cortex
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Če upoštevate, da je možganska skorja
05:56
is the seat of functions like
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središče funkcij, kot so zavedanje
06:00
awareness and logical and abstract reasoning,
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ter logično in abstraktno mišljenje,
06:03
and that 16 billion is the most neurons
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in da je 16 milijard največ nevronov
06:06
that any cortex has,
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v kateri koli možganski skorji,
06:08
I think this is the simplest explanation
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je po moje to najenostavnejša razlaga
06:10
for our remarkable cognitive abilities.
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za naše izredne kognitivne zmožnosti.
Toda prav tako je pomembno,
kaj teh 86 milijard nevronov pomeni.
kaj teh 86 milijard nevronov pomeni.
06:13
But just as important is what
the 86 billion neurons mean.
the 86 billion neurons mean.
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Ker smo odkrili, da lahko razmerje
06:16
Because we found that the relationship
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med velikostjo možganov
in številom njihovih nevronov
in številom njihovih nevronov
06:18
between the size of the brain
and its number of neurons
and its number of neurons
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06:20
could be described mathematically,
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opišemo z matematičnimi odnosi,
smo lahko izračunali,
kakšni bi bili človeški možgani,
kakšni bi bili človeški možgani,
06:22
we could calculate what a human brain
162
370355
2218
06:24
would look like if it was made like a rodent brain.
163
372573
2674
če bi bili zgrajeni kot možgani glodavcev.
06:27
So, a rodent brain with 86 billion neurons
164
375247
3574
Možgani glodavcev
s 86 milijardami nevronov
s 86 milijardami nevronov
06:30
would weigh 36 kilos.
165
378821
3121
bi tehtali 36 kilogramov.
06:33
That's not possible.
166
381942
1633
To ni možno.
06:35
A brain that huge would be crushed
167
383575
1906
Tako velike možgane bi uničila
06:37
by its own weight,
168
385481
1184
njihova lastna teža
06:38
and this impossible brain would go
169
386665
1587
in ti možgani bi bili
06:40
in the body of 89 tons.
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388252
3771
v telesu, ki tehta 89 ton.
06:44
I don't think it looks like us.
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2134
To ne izgleda ravno kot mi.
06:46
So this brings us to a very important
conclusion already,
conclusion already,
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394157
2553
To nas privede
do že zelo pomembnega zaključka,
do že zelo pomembnega zaključka,
06:48
which is that we are not rodents.
173
396710
2647
in sicer, da nismo glodavci.
06:51
The human brain is not a large rat brain.
174
399357
3268
Človeški možgani
niso veliki možgani podgane.
niso veliki možgani podgane.
06:54
Compared to a rat, we might seem special, yes,
175
402625
2628
V primerjavi s podgano
seveda izgledamo posebni,
seveda izgledamo posebni,
06:57
but that's not a fair comparison to make,
176
405253
2220
toda ta primerjava ni pravična,
06:59
given that we know that we are not rodents.
177
407473
2089
saj vemo, da nismo glodavci.
07:01
We are primates,
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409562
1390
Primati smo,
07:02
so the correct comparison is to other primates.
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410952
2774
torej je bolj pravilna primerjava
z drugimi primati.
z drugimi primati.
07:05
And there, if you do the math,
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413726
1227
In če tu vse izračunate,
07:06
you find that a generic primate
181
414953
2786
boste odkrili, da bi povprečni primat
07:09
with 86 billion neurons
182
417739
1930
s 86 milijardami nevronov
07:11
would have a brain of about 1.2 kilos,
183
419669
3003
imel možgane,
ki bi tehtali okrog 1,2 kilograma,
ki bi tehtali okrog 1,2 kilograma,
07:14
which seems just right,
184
422672
1889
kar se zdi ravno prav
07:16
in a body of some 66 kilos,
185
424561
1972
za telo s približno 66-imi kilogrami,
07:18
which in my case is exactly right,
186
426533
2645
kar velja ravno zame,
07:21
which brings us to a very unsurprising
187
429178
2620
kar nas pripelje do nepresenetljivega,
07:23
but still incredibly important conclusion:
188
431798
2969
toda izredno pomembnega zaključka:
07:26
I am a primate.
189
434767
1341
Primat sem.
07:28
And all of you are primates.
190
436108
2698
In tudi vi ste primati.
07:30
And so was Darwin.
191
438806
1900
In tudi Darwin je bil.
07:32
I love to think that Darwin
would have really appreciated this.
would have really appreciated this.
192
440706
2940
Rada si mislim, da bi Darwin
zelo cenil te zaključke.
zelo cenil te zaključke.
07:35
His brain, like ours,
193
443646
1967
Njegovi možgani, tako kot naši,
07:37
was made in the image of other primate brains.
194
445613
3511
so bili narejeni
po zgledu drugih primatov.
po zgledu drugih primatov.
07:41
So the human brain may be remarkable, yes,
195
449124
2302
Človeški možgani so gotovo neverjetni,
07:43
but it is not special in its number of neurons.
196
451426
2781
toda naše število nevronov
ni nič posebnega.
ni nič posebnega.
07:46
It is just a large primate brain.
197
454207
1855
Imamo le velike možgane primatov.
07:48
I think that's a very humbling and sobering thought
198
456062
3044
Mislim, da nas lahko ta misel strezni
in nas naredi bolj ponižne
in nas naredi bolj ponižne
07:51
that should remind us of our place in nature.
199
459106
3063
ter nas spomni na naše mesto v naravi.
07:54
Why does it cost so much energy, then?
200
462169
2644
Zakaj nas potem možgani
stanejo toliko energije?
stanejo toliko energije?
07:56
Well, other people have figured out
201
464813
1447
Drugi ljudje so ugotovili,
07:58
how much energy the human brain
202
466260
1503
koliko porabijo človeški možgani
07:59
and that of other species costs,
203
467763
1407
in koliko možgani drugih vrst.
08:01
and now that we knew how many neurons
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469170
1652
Ko smo izvedeli, koliko nevronov
je v možganih, smo naredili izračun.
je v možganih, smo naredili izračun.
08:02
each brain was made of, we could do the math.
205
470822
2342
08:05
And it turns out that both human
206
473164
1866
Izkazalo se je, da tako človeški možgani
08:07
and other brains cost about the same,
207
475030
2823
kot možgani drugih vrst
porabijo skoraj enako,
porabijo skoraj enako,
08:09
an average of six calories
per billion neurons per day.
per billion neurons per day.
208
477853
3421
v povprečju 6 kalorij
na milijardo nevronov na dan.
na milijardo nevronov na dan.
08:13
So the total energetic cost of a brain
209
481274
2139
Skupna energijska poraba možganov
08:15
is a simple, linear function
210
483413
2034
je preprosta linearna funkcija
08:17
of its number of neurons,
211
485447
1709
števila njihovih nevronov
08:19
and it turns out that the human brain
212
487156
2183
in izkazalo se je, da človeški možgani
08:21
costs just as much energy as you would expect.
213
489339
3841
porabijo prav toliko energije,
kot bi pričakovali.
kot bi pričakovali.
08:25
So the reason why the human brain
214
493180
2091
Razlog, da človeški možgani
08:27
costs so much energy is simply because
215
495271
1672
porabijo toliko energije,
je v tem, da imajo
veliko število nevronov.
veliko število nevronov.
08:28
it has a huge number of neurons,
216
496943
1983
08:30
and because we are primates
217
498926
1485
Ker smo primati
08:32
with many more neurons for a given body size
218
500411
2499
z dosti več nevroni
glede na velikost telesa
glede na velikost telesa
08:34
than any other animal,
219
502910
1522
kot katerakoli druga žival,
08:36
the relative cost of our brain is large,
220
504432
3540
je tudi povprečna poraba možganov velika,
08:39
but just because we're primates,
not because we're special.
not because we're special.
221
507972
3001
toda le zato, ker smo primati,
in ne, ker smo posebni.
in ne, ker smo posebni.
08:42
Last question, then:
222
510973
1190
Še zadnje vprašanje:
08:44
how did we come by this
remarkable number of neurons,
remarkable number of neurons,
223
512163
3115
Kako smo prišli do tega
izrednega števila nevronov,
izrednega števila nevronov,
08:47
and in particular, if great apes
224
515278
1900
in natančneje, če so velike opice
08:49
are larger than we are,
225
517178
1555
večje od nas,
08:50
why don't they have a larger brain
than we do, with more neurons?
than we do, with more neurons?
226
518733
3765
zakaj nimajo večjih možganov,
z več nevroni?
z več nevroni?
08:54
When we realized how much expensive it is
227
522498
2090
Ko smo se zavedli, kako drago je
08:56
to have a lot of neurons in the brain, I figured,
228
524588
2333
imeti veliko nevronov v možganih,
sem sklepala,
sem sklepala,
08:58
maybe there's a simple reason.
229
526921
2003
da mogoče za to obstaja preprost razlog.
09:00
They just can't afford the energy
230
528924
1683
Opice si ne morejo privoščiti energije
09:02
for both a large body
and a large number of neurons.
and a large number of neurons.
231
530607
2950
za veliko telo
in za veliko število nevronov.
in za veliko število nevronov.
09:05
So we did the math.
232
533557
1429
Zato smo se lotili računanja.
09:06
We calculated on the one hand
233
534986
1600
Izračunali smo,
09:08
how much energy a primate gets per day
234
536586
1941
koliko energije primati dobijo na dan
09:10
from eating raw foods,
235
538527
1350
s surovo hrano,
09:11
and on the other hand, how much energy
236
539877
2037
koliko energije porabi
09:13
a body of a certain size costs
237
541914
1764
telo določene velikosti
09:15
and how much energy a brain of a
certain number of neurons costs,
certain number of neurons costs,
238
543678
3387
in koliko energije porabijo možgani
z določenim številom nevronov.
z določenim številom nevronov.
09:19
and we looked for the combinations
239
547065
1489
Iskali smo kombinacije
09:20
of body size and number of brain neurons
240
548554
2411
velikosti telesa in števila nevronov,
ki bi si jih primati lahko privoščili,
09:22
that a primate could afford
241
550965
1270
09:24
if it ate a certain number of hours per day.
242
552235
2548
če bi določeno število ur dnevno
porabili za prehrano.
porabili za prehrano.
09:26
And what we found is that
243
554783
1816
Ugotovili smo,
09:28
because neurons are so expensive,
244
556599
1712
da ker so nevroni tako dragi,
09:30
there is a tradeoff between
body size and number of neurons.
body size and number of neurons.
245
558311
3370
obstaja kompromis med velikostjo telesa
in številom nevronov.
in številom nevronov.
09:33
So a primate that eats eight hours per day
246
561681
2951
Primati, ki se prehranjujejo
osem ur na dan,
osem ur na dan,
09:36
can afford at most 53 billion neurons,
247
564632
3024
si lahko privoščijo 53 milijard nevronov,
toda potem njihovo telo ne more presegati
09:39
but then its body cannot be any bigger
248
567656
1727
09:41
than 25 kilos.
249
569383
1954
25 kilogramov teže.
09:43
To weigh any more than that,
250
571337
1701
Če bi tehtali več,
09:45
it has to give up neurons.
251
573038
1769
bi se morali odpovedati nevronom.
09:46
So it's either a large body
252
574807
2653
Imamo lahko torej veliko telo
09:49
or a large number of neurons.
253
577460
1495
ali pa veliko število nevronov.
09:50
When you eat like a primate,
254
578955
1365
Če jemo kot primati,
09:52
you can't afford both.
255
580320
2236
si drugega ne moremo privoščiti.
09:54
One way out of this metabolic limitation
256
582556
1964
En izhod iz te metabolične omejitve bi bil
09:56
would be to spend even more hours per day eating,
257
584520
3401
porabiti še več ur na dan
za prehranjevanje,
za prehranjevanje,
09:59
but that gets dangerous,
258
587921
1363
toda to postane nevarno
10:01
and past a certain point, it's just not possible.
259
589284
2719
in od neke točke ni več možno.
10:04
Gorillas and orangutans, for instance,
260
592003
1537
Gorile in orangutani
si na primer lahko privoščijo
30 milijard nevronov
30 milijard nevronov
10:05
afford about 30 billion neurons
261
593540
1923
10:07
by spending eight and a half hours per day eating,
262
595463
2966
s prehranjevanjem 8 in pol ur na dan,
10:10
and that seems to be about as much as they can do.
263
598429
3116
kar se zdi največ kar lahko naredijo.
10:13
Nine hours of feeding per day
264
601545
1791
Devet ur na dan za hranjenje
10:15
seems to be the practical limit for a primate.
265
603336
3271
se zdi stvarna omejitev za primate.
10:18
What about us?
266
606607
1791
Kaj pa mi?
10:20
With our 86 billion neurons
267
608398
1600
S 86 milijardami nevronov
10:21
and 60 to 70 kilos of body mass,
268
609998
3035
in 60 do 70 kilogramov telesne mase
10:25
we should have to spend over nine hours
269
613033
3561
bi morali preživeti več kot 9 ur na dan
10:28
per day every single day feeding,
270
616594
3575
za prehranjevanje,
10:32
which is just not feasible.
271
620169
2039
kar preprosto ni uresničljivo.
10:34
If we ate like a primate,
272
622208
1834
Če bi jedli kot primati,
10:36
we should not be here.
273
624042
2253
nas ne bi bilo.
10:38
How did we get here, then?
274
626295
2127
Kako smo potem prišli sem?
10:40
Well, if our brain costs just as much energy
275
628422
2735
Če nas možgani stanejo toliko energije,
10:43
as it should, and if we can't spend
276
631157
1723
kot bi nas morali
in če ne moremo preživeti
in če ne moremo preživeti
10:44
every waking hour of the day feeding,
277
632880
3674
vsake sleherne ure za hranjenje,
10:48
then the only alternative, really,
278
636554
1911
potem je edina alternativa
10:50
is to somehow get more energy
279
638465
1958
dobiti več energije
10:52
out of the same foods.
280
640423
1953
iz enake hrane.
10:54
And remarkably, that matches exactly
281
642376
3800
In neverjetno,
o se pravzaprav ujema s tem,
o se pravzaprav ujema s tem,
10:58
what our ancestors are believed to have invented
282
646176
3037
kar so naši predniki najverjetneje izumili
11:01
one and a half million years ago,
283
649213
1839
pred enim in pol milijonom let,
11:03
when they invented cooking.
284
651052
2782
ko so izumili kuhanje.
11:05
To cook is to use fire
285
653834
1970
Kuhati pomeni uporabiti ogenj,
11:07
to pre-digest foods outside of your body.
286
655804
3800
da predhodno predelamo hrano
preden ta vstopi v naše telo.
preden ta vstopi v naše telo.
11:11
Cooked foods are softer, so they're easier to chew
287
659604
2606
Kuhana hrana je mehkejša,
torej tudi lažja za žvečenje
torej tudi lažja za žvečenje
11:14
and to turn completely into mush in your mouth,
288
662210
2563
in se v naših ustih lažje spremeni v kašo,
11:16
so that allows them to be completely digested
289
664773
2152
kar hrani dovoli,
da je popolnoma presnovljena
da je popolnoma presnovljena
11:18
and absorbed in your gut,
290
666925
1436
in se absorbira v naše črevo,
11:20
which makes them yield much more
energy in much less time.
energy in much less time.
291
668361
3655
zaradi česar pridobimo
več energije v krajšem času.
več energije v krajšem času.
11:24
So cooking frees time for us to do
292
672016
2489
Zaradi kuhanja pridobimo čas,
11:26
much more interesting things with our day
293
674505
2062
da svoj dan in svoje nevrone
11:28
and with our neurons
294
676567
1480
porabimo za kaj bolj zanimivega,
11:30
than just thinking about food,
295
678047
1905
kot da le mislimo na hrano,
11:31
looking for food, and gobbling down food
296
679952
1704
iščemo hrano in goltamo hrano
11:33
all day long.
297
681656
1225
ves ljubi dan.
11:34
So because of cooking, what once was
298
682881
2499
Zaradi kuhanja
11:37
a major liability, this large,
299
685380
2353
je nekdanja omejitev, ti ogromni,
11:39
dangerously expensive brain with a lot of neurons,
300
687733
3033
nevarno dragi možgani
z veliko nevroni,
z veliko nevroni,
11:42
could now become a major asset,
301
690766
2036
postala ogromna prednost.
11:44
now that we could both afford
the energy for a lot of neurons
the energy for a lot of neurons
302
692802
3251
Zdaj si lahko privoščimo
tako energijo za dosti nevronov
tako energijo za dosti nevronov
11:48
and the time to do interesting things with them.
303
696056
2503
kot tudi čas,
da z njimi delamo zanimive reči.
da z njimi delamo zanimive reči.
Zato mislim, da to razloži,
zakaj so človeški možgani
zakaj so človeški možgani
11:50
So I think this explains why the human brain
304
698559
1974
11:52
grew to become so large so fast in evolution,
305
700533
3240
postali tako veliki
tako hitro v evoluciji,
tako hitro v evoluciji,
11:55
all of the while remaining just a primate brain.
306
703773
3897
medtem ko so še vedno le možgani primatov.
Ker si zaradi kuhanja zdaj lahko privoščimo
tako velike možgane,
tako velike možgane,
11:59
With this large brain now affordable by cooking,
307
707670
2774
12:02
we went rapidly from raw foods to culture,
308
710444
2913
smo hitro prešli s surove prehrane
na kulturo,
na kulturo,
12:05
agriculture, civilization, grocery stores,
309
713357
2606
kmetijstvo, civilizacijo, trgovine,
12:07
electricity, refrigerators,
310
715963
1625
elektriko, hladilnike,
vse te reči, ki nam danes dovoljujejo
12:09
all of those things that nowadays
311
717588
1607
12:11
allow us to get all the energy we need
312
719195
2042
da dobimo energijo,
potrebno za celotni dan,
potrebno za celotni dan,
12:13
for the whole day in a single sitting
313
721237
2782
le z enim obiskom
12:16
at your favorite fast food joint.
314
724019
2954
svojega najljubšega kotička s hitro hrano.
12:18
So what once was a solution
315
726973
2437
Kar je nekoč predstavljalo rešitev,
12:21
now became the problem,
316
729410
1699
je danes postalo problem
12:23
and ironically, we look for the solution in raw food.
317
731109
5517
in ironično sami rešitev
iščemo v surovi prehrani.
iščemo v surovi prehrani.
12:28
So what is the human advantage?
318
736626
2556
Kaj pa je prednost ljudi?
12:31
What is it that we have
319
739182
1503
Kaj imamo,
12:32
that no other animal has?
320
740685
2535
česar nima nobena druga žival?
12:35
My answer is that we have the largest number
321
743220
2348
Moj odgovor je, da imamo največje število
12:37
of neurons in the cerebral cortex,
322
745568
1472
nevronov v možganski skorji
12:39
and I think that's the simplest explanation
323
747040
1844
in po moje je to najlažja razlaga
12:40
for our remarkable cognitive abilities.
324
748884
2013
za naše izjemne kognitivne sposobnosti.
12:42
And what is it that we do that no other animal does,
325
750897
3227
In kaj mi delamo,
česar nobena druga žival ne počne,
česar nobena druga žival ne počne,
12:46
and which I believe was fundamental
326
754124
1969
in kar je postavilo temelje,
12:48
to allow us to reach that large,
327
756093
3083
da smo lahko dosegli tako veliko,
12:51
largest number of neurons in the cortex?
328
759176
2222
največje število nevronov
v možganski skorji?
v možganski skorji?
12:53
In two words, we cook.
329
761398
2215
Z eno besedo - kuhamo.
12:55
No other animal cooks its food. Only humans do.
330
763613
3566
Nobena druga žival si ne kuha hrane.
Le ljudje si jo.
Le ljudje si jo.
12:59
And I think that's how we got to become human.
331
767179
2870
In mislim, da smo zaradi tega
lahko postali ljudje.
lahko postali ljudje.
Pri proučevanju človeških možganov
sem o hrani začela drugače razmišljati.
sem o hrani začela drugače razmišljati.
13:02
Studying the human brain changed
the way I think about food.
the way I think about food.
332
770049
2460
13:04
I now look at my kitchen,
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Zdaj pogledam svojo kuhinjo,
13:06
and I bow to it,
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se ji priklonim
13:07
and I thank my ancestors for coming up
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in se zahvalim svojim prednikom
za izum tega,
za izum tega,
13:09
with the invention that probably made us humans.
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kar nas je verjetno naredilo človeške.
13:11
Thank you very much.
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Hvala lepa.
13:13
(Applause)
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(Aplavz)
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