ABOUT THE SPEAKER
Suzana Herculano-Houzel - Neuroscientist
Suzana 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.

More profile about the speaker
Suzana Herculano-Houzel | Speaker | TED.com
TEDGlobal 2013

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

Suzana Herculano-Houzel: Zer du hain berezia giza garunak?

Filmed:
3,044,795 views

Giza garuna harrigarria da. Gure gorputzaren tamainarako oso handia da, duen pisurako energia kantitate izugarri handia erabiltzen du eta garun azal izugarri dentso bat du. Baina, zergatik? Suzana Herculano-Houzel neurozientzialariak detektibe bat bailitzan misterio honen barnean gidatuko gaitu. "Garun-zopa" egitean, ondorio harrigarri batera heltzen da.
- Neuroscientist
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.

Zer da giza burmuina
hain berezia egiten duena?
00:12
What is so special about the human brain?
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00:15
Why is it that we study other animals
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Zergatik ikertzen ditugu guk
beste animaliak
00:17
instead of them studying us?
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eta haiek ez gaituzte gu ikertzen?
Zer du giza burmuinak edo zer egiten du
00:19
What does a human brain have or do
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00:21
that no other brain does?
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besteenak egiten ez duenik?
00:23
When I became interested
in these questions about 10 years ago,
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Gai hauetaz interesatzen hasi nintzenean,
duela 10 urte,
00:26
scientists thought they knew
what different brains were made of.
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zientifikoek uste zuten bazekitela
garunak nola eginda zeuden.
00:28
Though it was based on very little evidence,
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Ebidentzia gutxi izan arren,
00:30
many scientists thought that all mammalian brains,
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zientifiko askok zioten
ugaztunen garunak,
00:32
including the human brain,
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baita gizakiena ere,
berdin osatuak zeudela
00:34
were made in the same way,
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00:35
with a number of neurons that was always
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eta garunaren tamainarekiko
proportzionala zen
00:37
proportional to the size of the brain.
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neurona kopurua zutela.
00:39
This means that two brains of the same size,
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Hau da, tamaina bereko bi garunek,
00:41
like these two, with a respectable 400 grams,
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400 gramoko bi garun hauek esaterako,
00:45
should have similar numbers of neurons.
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neurona kopuru bertsua
izan beharko luketela.
00:47
Now, if neurons are the functional
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Baina neuronak garuneko
00:49
information processing units of the brain,
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informazioaren prozesamenduaren
unitate funtzionalak badira,
00:52
then the owners of these two brains
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garun bi hauen jabeek
00:54
should have similar cognitive abilities.
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gaitasun kognitibo antzekoak
izan beharko lituzkete.
00:56
And yet, one is a chimp,
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Baina bata txinpantzea da,
00:59
and the other is a cow.
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eta bestea behi bat.
01:01
Now maybe cows have a really rich
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Posible da behiek barne bizitza
01:04
internal mental life and are so smart
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sakon bat izatea,
eta hain azkarrak izanik
01:06
that they choose not to let us realize it,
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guri hortaz ohartzen ez uztea
erabaki izana,
01:10
but we eat them.
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baina guk eurak jaten ditugu.
01:11
I think most people will agree
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Nirekin ados egongo zarete
01:13
that chimps are capable of much more complex,
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txinpantzeek behiek baino jokabide
konplexu, elaboratu eta malguagoak
01:15
elaborate and flexible behaviors than cows are.
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burutzeko gai direla.
01:18
So this is a first indication that the
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"Garun guztiak modu berean
osatuak daude" esaldia
01:20
"all brains are made the same way" scenario
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oso zuzena ez dela
01:22
is not quite right.
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erakusten du lehen puntu honek.
01:24
But let's play along.
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Baina jarrai dezagun.
01:25
If all brains were made the same way
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Garun denak berdin osatuak baleude,
01:27
and you were to compare animals
with brains of different sizes,
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tamaina desberdineko garundun
animaliak konparatuz gero,
01:30
larger brains should always have more neurons
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garun handiek txikiek baino
neurona gehiago
01:32
than smaller brains,
and the larger the brain,
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izan beharko lituzkete.
Gero eta handiagoa,
01:34
the more cognitively able its owner should be.
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orduan eta gaitasun kognitibo handiagoa
izango luke garunaren jabeak.
01:37
So the largest brain around should also be
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Hori horrela balitz, garun handienak
01:39
the most cognitively able.
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gaitasun kognitibo handiena izango luke.
01:42
And here comes the bad news:
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Eta, hemen datoz berri txarrak:
01:43
Our brain, not the largest one around.
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Gure garuna ez da guztietan handiena.
01:46
It seems quite vexing.
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Honek nahasgarria dirudi.
01:47
Our brain weighs between 1.2 and 1.5 kilos,
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Gure garunak 1, 2
eta 1,5 kg artean pisatzen du,
01:50
but elephant brains weigh between four and five kilos,
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elefanteen garunak
4 eta 5 kg artean pisatzen du,
01:54
and whale brains can weigh up to nine kilos,
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eta baleen garunak
9 kg arteko pisua har dezake.
01:56
which is why scientists used to resort to saying
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Guzti honengatik,
zientifikoek gure garuna
berezia zela esaten zuten
02:01
that our brain must be special
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02:03
to explain our cognitive abilities.
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gure gaitasun kognitiboak azaltzean.
02:06
It must be really extraordinary,
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Benetan ezohikoa izan behar du bai,
02:09
an exception to the rule.
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arauaren salbuespena.
02:11
Theirs may be bigger, but ours is better,
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Beraiena handiagoa izango da bai,
baina gurea hobea da,
02:14
and it could be better, for example,
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eta hobea izan zitekeen,
hau da,
izan behar lukeena baino
handiagoa omen delako,
02:16
in that it seems larger than it should be,
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02:18
with a much larger cerebral cortex
than we should have
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gure gorputzen tamainagatik
izan beharko genukeena baino
02:21
for the size of our bodies.
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kortex askoz handiagoa baitugu.
02:22
So that would give us extra cortex
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Garun kortex estra omen dugu,
02:24
to do more interesting things
than just operating the body.
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gorputza kudeatzeko baino
gauza interesgarriagoak egiteko.
02:27
That's because the size of the brain
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Normalean, garunaren tamaina
02:29
usually follows the size of the body.
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gorputzaren tamainaren araberakoa da.
02:31
So the main reason for saying that
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Beraz, gure garuna beharko lukeena baino
02:33
our brain is larger than it should be
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handiagoa dela esateko arrazoi nagusia,
02:35
actually comes from comparing ourselves
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beste hominidoekin egindako
konparaketetatik dator.
02:37
to great apes.
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Gorilak gu baino 2 edo 3 aldiz
handiagoak izan daitezke.
02:39
Gorillas can be two to three times larger than we are,
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02:41
so their brains should also be larger than ours,
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Bere garunak gureak baino
handiagoak izan beharko lukete
02:44
but instead it's the other way around.
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baina aurkakoa gertatzen da.
02:46
Our brain is three times larger than a gorilla brain.
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Gure garuna gorilena baino
hiru aldiz handiagoa da.
02:49
The human brain also seems special
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Giza garuna berezia dirudi ere
02:51
in the amount of energy that it uses.
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erabiltzen duen
energia kantitateagatik.
02:53
Although it weighs only two percent of the body,
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Gorputzaren pisuaren
%2a soilik izan arren,
02:56
it alone uses 25 percent of all the energy
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berak bakarrik gorputzak eguneroko
funtzioetarako darabilen
02:59
that your body requires to run per day.
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energia guztiaren %25 behar du.
03:02
That's 500 calories out of a total of 2,000 calories,
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Hori 2000 kalorietatik 500 litzateke,
03:05
just to keep your brain working.
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garuna funtzionamenduan izateko bakarrik.
03:07
So the human brain is larger than it should be,
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Beraz, giza garuna beharko
lukeena baino handiagoa da,
behar lukeena baino
energia gehiago erabiltzen du,
03:10
it uses much more energy than it should,
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03:12
so it's special.
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eta berezia da.
03:14
And this is where the story started to bother me.
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Orain istorio hau gogaikarri
bihurtzen hasi zen.
03:16
In biology, we look for rules
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Biologian arauak bilatzen ditugu,
03:18
that apply to all animals and to life in general,
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animalia guztiei eta bizitzari
oro har aplikatzekoak.
03:21
so why should the rules of evolution
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Zergatik aplikatu beharko zaizkie
03:23
apply to everybody else but not to us?
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eboluzioaren arauak
espezie guztiei guri izan ezik?
03:26
Maybe the problem was with the basic assumption
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Agian arazoa oinarrizko ustean zegoen,
agian garun denak
ez daude berdin osatuak.
03:29
that all brains are made in the same way.
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03:30
Maybe two brains of a similar size
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Agian tamaina bereko bi garun
03:32
can actually be made of
very different numbers of neurons.
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neurona kantitate ezberdinez
osatuta egon daitezke.
03:35
Maybe a very large brain
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Oso handia den garun batek
03:36
does not necessarily have more neurons
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agian ez du
txikiago batek baino
neurona gehiago izan behar.
03:38
than a more modest-sized brain.
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03:40
Maybe the human brain
actually has the most neurons
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Agian gizakion garunak neurona
kantitate handiena du
03:43
of any brain, regardless of its size,
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bere tamainak axolarik izan gabe,
03:46
especially in the cerebral cortex.
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batez ere kortexean.
03:48
So this to me became
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Ondorioz, guzti hau erantzun beharreko
kontu garrantzitsu bihurtu zen.
03:50
the important question to answer:
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03:51
how many neurons does the human brain have,
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Zenbat neurona ditu giza garunak,
03:54
and how does that compare to other animals?
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eta nola konpara dezakegu
beste animaliekin?
Posible da zuetako batzuk
nonbait irakurri edo entzun izana
03:56
Now, you may have heard or read somewhere
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03:59
that we have 100 billion neurons,
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100 mila milioi neurona ditugula.
04:01
so 10 years ago, I asked my colleagues
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Duela 10 urte,
lankideei galdetu nien
ea bazekiten zifra hori
nondik zetorren.
04:03
if they knew where this number came from.
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04:05
But nobody did.
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Inork ez zekien.
04:06
I've been digging through the literature
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Zifra horren jatorriaren bila
04:08
for the original reference for that number,
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jardun nintzen
erreferentzia-bibliografian,
04:10
and I could never find it.
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baina sekula ez nuen aurkitu.
04:11
It seems that nobody had actually ever counted
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Badirudi inork ez zuela benetan
giza garunaren
04:14
the number of neurons in the human brain,
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neurona kopurua zenbatu,
04:16
or in any other brain for that matter.
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ez eta beste edozein garunetako
neurona kopurua ere.
04:18
So I came up with my own way
to count cells in the brain,
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Garuneko zelulak kontatu ahal izateko
formula bat sortu nuen.
04:22
and it essentially consists of
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Oinarrian zera egin behar da:
04:24
dissolving that brain into soup.
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garuna disolbatu, zopa bihurtu arte.
04:27
It works like this:
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Horrela funtzionatzen du:
04:29
You take a brain, or parts of that brain,
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garun bat edo garun zati batzuk hartu
04:32
and you dissolve it in detergent,
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eta garbigarritan disolbatzen da.
04:34
which destroys the cell membranes
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Honek ehunak suntsitzen ditu
04:35
but keeps the cell nuclei intact,
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baina zelularen nukleoa osorik
mantentzen du.
04:38
so you end up with a suspension of free nuclei
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Horrela, nukleoarekin soilik
geratzen zara.
04:41
that looks like this,
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Nukleoak itxura hau du,
zopa baten antzekoa da.
04:43
like a clear soup.
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04:44
This soup contains all the nuclei
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Zopa honek, arratoi baten
garuna zenak,
04:46
that once were a mouse brain.
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nukleo guztiak ditu.
04:48
Now, the beauty of a soup is that because it is soup,
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Zoparen edertasuna zera da, zopa denez,
04:51
you can agitate it and make those nuclei
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berau nahastu dezakezula,
eta horrela nukleo guzti horiek
04:54
be distributed homogeneously in the liquid,
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likidotan homogeneoki banatu.
04:56
so that now by looking under the microscope
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Soluzio homogeneo honen
04:58
at just four or five samples
of this homogeneous solution,
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lau edo bost lagin
mikroskopiotik behatzean,
05:02
you can count nuclei, and therefore tell
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nukleoak kontatu ahal dira,
eta garun horrek
05:05
how many cells that brain had.
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zenbat zelula zituen jakin.
05:06
It's simple, it's straightforward,
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Sinplea da, erraza,
eta benetan azkarra.
05:08
and it's really fast.
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05:09
So we've used that method to count neurons
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Metodo honekin
dozenaka espezieren
05:11
in dozens of different species so far,
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neuronak kontatu ditugu,
05:14
and it turns out that all brains
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eta zera ikusi dugu,
05:15
are not made the same way.
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garunak ez daudela modu berean osatuta.
Azter ditzagun
karraskariak eta primateak.
05:18
Take rodents and primates, for instance:
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05:20
In larger rodent brains, the average size
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Karraskarien garun handienetan,
handitu egiten da
05:22
of the neuron increases,
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neuronen batezbesteko tamaina.
05:24
so the brain inflates very rapidly
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Beraz, garuna azkar puzten da
05:27
and gains size much faster than it gains neurons.
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eta tamainaz handitzen da,
neuronak gehitu baino.
Primateen garunak, berriz,
05:30
But primate brains gain neurons
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neuronak gehitzen ditu
neuronen tamaina handitu barik.
05:32
without the average neuron becoming any larger,
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05:34
which is a very economical way
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Garunari neuronak gehitzeko
modu oso ekonomikoa da.
05:35
to add neurons to your brain.
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Beraz, primate baten garunak
05:37
The result is that a primate brain
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neurona gehiago izango du
tamaina bereko karraskari batenak baino.
05:39
will always have more neurons than
a rodent brain of the same size,
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05:42
and the larger the brain,
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Garuna gero eta handiagoa izan,
05:44
the larger this difference will be.
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gero eta handiagoa izango da aldea.
05:46
Well, what about our brain then?
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Zer gertatzen da gure garunean?
05:48
We found that we have, on average,
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Zera aurkitu dugu: batez beste
86 mila milioi neurona ditugu.
05:50
86 billion neurons,
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05:51
16 billion of which are in the cerebral cortex,
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Hauetako 16 mila milioi
garun kortexean aurkitzen dira,
05:54
and if you consider that the cerebral cortex
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Kontuan hartuz kortexean daudela
05:56
is the seat of functions like
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kontzientzia, arrazonamendu logikoa,
06:00
awareness and logical and abstract reasoning,
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abstraktua eta antzeko funtzioak,
06:03
and that 16 billion is the most neurons
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eta ez dagoela 16 mila milioi
neurona baino gehiago
06:06
that any cortex has,
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duen kortexik,
06:08
I think this is the simplest explanation
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uste dut hau dela
06:10
for our remarkable cognitive abilities.
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gure aparteko gaitasun kognitiboen
azalpen sinpleena.
06:13
But just as important is what
the 86 billion neurons mean.
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86 mila milioi neurona horien
esanahia ere garrantzitsua da.
06:16
Because we found that the relationship
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Aurkitu genuen garunaren tamainaren
06:18
between the size of the brain
and its number of neurons
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eta bere neurona kopuruaren
arteko erlazioa
06:20
could be described mathematically,
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matematikoki deskribatu daitekeela.
06:22
we could calculate what a human brain
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Giza garun bat karraskari batena balitz
06:24
would look like if it was made like a rodent brain.
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nolakoa izango zen
kalkulatu ahal izan genuen.
06:27
So, a rodent brain with 86 billion neurons
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Karraskari baten garunak
86 mila milioi neurona izango balitu,
06:30
would weigh 36 kilos.
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36 kg pisatuko lituzke.
06:33
That's not possible.
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Hori ezta posible.
06:35
A brain that huge would be crushed
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Hain garun handia bere pisuak
zanpatuko luke,
06:37
by its own weight,
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06:38
and this impossible brain would go
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eta garun hau
06:40
in the body of 89 tons.
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89 tonatako gorputz batekin
etorriko litzake.
06:44
I don't think it looks like us.
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Horrek ez luke gure antzik izango.
06:46
So this brings us to a very important
conclusion already,
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Guzti honek
ondorio nagusi batera garamatza:
06:48
which is that we are not rodents.
173
396710
2647
ez garela karraskariak.
06:51
The human brain is not a large rat brain.
174
399357
3268
Giza garuna
ez da arratoi garun erraldoi bat.
06:54
Compared to a rat, we might seem special, yes,
175
402625
2628
Arratoi batekin alderatuta
bereziak izan gaitezke,
06:57
but that's not a fair comparison to make,
176
405253
2220
baina ez da alderaketa justua,
06:59
given that we know that we are not rodents.
177
407473
2089
baitakigu ez garela karraskariak.
07:01
We are primates,
178
409562
1390
Primateak gara,
07:02
so the correct comparison is to other primates.
179
410952
2774
beraz alderaketa justua
beste primateekin litzateke.
07:05
And there, if you do the math,
180
413726
1227
Kalkuluak hau ematen du:
07:06
you find that a generic primate
181
414953
2786
86 mila milioi neurona lituzkeen
primate batek
07:09
with 86 billion neurons
182
417739
1930
07:11
would have a brain of about 1.2 kilos,
183
419669
3003
gutxi gora behera 1,2 kg-ko
garuna edukiko luke
07:14
which seems just right,
184
422672
1889
onargarria dena,
eta 66 kg-ko gorputza.
07:16
in a body of some 66 kilos,
185
424561
1972
07:18
which in my case is exactly right,
186
426533
2645
Horixe da nire kasua hain zuzen ere.
07:21
which brings us to a very unsurprising
187
429178
2620
Guzti honek harrigarria ez,
baina garrantzitsua den
beste ondorio batera garamatza:
07:23
but still incredibly important conclusion:
188
431798
2969
07:26
I am a primate.
189
434767
1341
primate bat naiz.
07:28
And all of you are primates.
190
436108
2698
Eta zuek guztiak primateak zarete.
07:30
And so was Darwin.
191
438806
1900
Darwin ere primatea zen.
07:32
I love to think that Darwin
would have really appreciated this.
192
440706
2940
Darwinek hau
benetan gustukoa izango zuen.
07:35
His brain, like ours,
193
443646
1967
Bere garuna, gurea bezala,
07:37
was made in the image of other primate brains.
194
445613
3511
beste primateen garunaren
itxurara egina zegoen.
07:41
So the human brain may be remarkable, yes,
195
449124
2302
Beraz, giza garuna apartekoa da
07:43
but it is not special in its number of neurons.
196
451426
2781
baina ez da berezia
neurona kopuruaren aldetik.
07:46
It is just a large primate brain.
197
454207
1855
Primate handi baten garuna baino ez da.
07:48
I think that's a very humbling and sobering thought
198
456062
3044
Pentsamendu apal
eta erakusgarria dela uste dut,
07:51
that should remind us of our place in nature.
199
459106
3063
naturan dugun lekua
gogoratzen digun pentsamendua.
07:54
Why does it cost so much energy, then?
200
462169
2644
Zergatik behar du hainbeste energia?
07:56
Well, other people have figured out
201
464813
1447
Beste batzuk ikertu dute
07:58
how much energy the human brain
202
466260
1503
gizakiaren eta beste espezieren garunek
behar duten energia.
07:59
and that of other species costs,
203
467763
1407
08:01
and now that we knew how many neurons
204
469170
1652
Badakigunez garunen neurona kopurua,
08:02
each brain was made of, we could do the math.
205
470822
2342
kalkulua egin dezakegu.
08:05
And it turns out that both human
206
473164
1866
Aurkitu da
giza garunak eta beste garunek
kantitate bera erabiltzen dutela:
08:07
and other brains cost about the same,
207
475030
2823
08:09
an average of six calories
per billion neurons per day.
208
477853
3421
batezbeste 6 kaloria eguneko
mila milioi neuronako.
Beraz, garun baten gastu energetikoa
08:13
So the total energetic cost of a brain
209
481274
2139
08:15
is a simple, linear function
210
483413
2034
neurona kantitatearen
funtzio lineal sinple bat da,
08:17
of its number of neurons,
211
485447
1709
08:19
and it turns out that the human brain
212
487156
2183
eta giza garunak
08:21
costs just as much energy as you would expect.
213
489339
3841
espero zitekeen beste
energia erabiltzen du.
08:25
So the reason why the human brain
214
493180
2091
Beraz, giza garunak hainbeste energia
08:27
costs so much energy is simply because
215
495271
1672
erabiltzearen arrazoia sinplea da,
08:28
it has a huge number of neurons,
216
496943
1983
neurona kantitate ikaragarria dugula.
08:30
and because we are primates
217
498926
1485
Primateak garelako,
neurona asko ditugu gure tamainarako
08:32
with many more neurons for a given body size
218
500411
2499
08:34
than any other animal,
219
502910
1522
beste animaliekin alderatuta.
08:36
the relative cost of our brain is large,
220
504432
3540
Gure garunaren gastu erlatiboa
izugarria da
08:39
but just because we're primates,
not because we're special.
221
507972
3001
baina hori primateak garelako da,
ez bereziak garelako.
08:42
Last question, then:
222
510973
1190
Beraz, azken galdera:
08:44
how did we come by this
remarkable number of neurons,
223
512163
3115
Nola heldu gara
neurona kopuru izugarri horretara?
08:47
and in particular, if great apes
224
515278
1900
Eta, are gehiago, primateak
gu baino handiagoak izanik,
08:49
are larger than we are,
225
517178
1555
08:50
why don't they have a larger brain
than we do, with more neurons?
226
518733
3765
zergatik ez dute gurea baino handiagoa
eta neurona gehiago dituen garuna?
08:54
When we realized how much expensive it is
227
522498
2090
Garunean hainbeste neurona izateak
08:56
to have a lot of neurons in the brain, I figured,
228
524588
2333
ze gastu zekarren ikusita,
arrazoi sinple bat zegoela
bururatu zitzaidan.
08:58
maybe there's a simple reason.
229
526921
2003
Beraiek ez dute nahikoa energia
09:00
They just can't afford the energy
230
528924
1683
gorputz handia
eta neurona kopuru handia mantentzeko.
09:02
for both a large body
and a large number of neurons.
231
530607
2950
Kalkulua egin genuen.
09:05
So we did the math.
232
533557
1429
Primate batek janari gordina janez
09:06
We calculated on the one hand
233
534986
1600
09:08
how much energy a primate gets per day
234
536586
1941
eguneko zenbat energia lortzen duen
09:10
from eating raw foods,
235
538527
1350
kalkulatu genuen.
09:11
and on the other hand, how much energy
236
539877
2037
Gero, zenbat energia beharko lukeen
09:13
a body of a certain size costs
237
541914
1764
tamaina zehatz bateko
gorputz batek
09:15
and how much energy a brain of a
certain number of neurons costs,
238
543678
3387
eta neurona kopuru konkretu batek
kalkulatu genuen.
Konbinaketak behatu genituen,
09:19
and we looked for the combinations
239
547065
1489
09:20
of body size and number of brain neurons
240
548554
2411
primate baten gorputz tamaina
eta garun-neurona
09:22
that a primate could afford
241
550965
1270
kopuruaren arteko konbinaketak
09:24
if it ate a certain number of hours per day.
242
552235
2548
egunean ordu zehatz batzuk
jaten emanez gero.
09:26
And what we found is that
243
554783
1816
Zera aurkitu genuen:
09:28
because neurons are so expensive,
244
556599
1712
neuronak hain garestiak direnez,
09:30
there is a tradeoff between
body size and number of neurons.
245
558311
3370
gorputzaren tamaina eta
neurona kantitatea konpentsatzen dira.
09:33
So a primate that eats eight hours per day
246
561681
2951
Egunean 8 ordu jaten pasatzen
dituen primate batek
09:36
can afford at most 53 billion neurons,
247
564632
3024
gehienez ere
53 mila milioi neurona izan ditzake,
baina bere gorputza ezin da
09:39
but then its body cannot be any bigger
248
567656
1727
09:41
than 25 kilos.
249
569383
1954
25 kg baino handiagoa izan.
09:43
To weigh any more than that,
250
571337
1701
Hori baino astunagoa izateko,
neurona gutxiago izan behar ditu.
09:45
it has to give up neurons.
251
573038
1769
09:46
So it's either a large body
252
574807
2653
Beraz, edo gorputz handi bat daukagu,
edo neurona kopuru handi bat.
09:49
or a large number of neurons.
253
577460
1495
09:50
When you eat like a primate,
254
578955
1365
Primate batek bezala jaten baduzu,
ezin dituzu bi gauzak izan.
09:52
you can't afford both.
255
580320
2236
09:54
One way out of this metabolic limitation
256
582556
1964
Muga metaboliko honetatik
askatzeko modu bat
09:56
would be to spend even more hours per day eating,
257
584520
3401
eguneko ordu gehiago
jaten pasatzea litzateke.
Baina hori arriskutsua da,
09:59
but that gets dangerous,
258
587921
1363
10:01
and past a certain point, it's just not possible.
259
589284
2719
eta puntu batetik aurrera ezinezkoa.
Gorilek eta orangutanek esaterako,
10:04
Gorillas and orangutans, for instance,
260
592003
1537
10:05
afford about 30 billion neurons
261
593540
1923
30 mila milioi neurona dituzte,
10:07
by spending eight and a half hours per day eating,
262
595463
2966
eta egunean 8 ordu eta erdi
jaten pasatzen dituzte.
10:10
and that seems to be about as much as they can do.
263
598429
3116
Hori da antza lor dezaketen gehiena.
10:13
Nine hours of feeding per day
264
601545
1791
Badirudi egunean
9 ordu jaten pasatzea dela
10:15
seems to be the practical limit for a primate.
265
603336
3271
primate baten muga praktikoa.
10:18
What about us?
266
606607
1791
Eta gurea?
10:20
With our 86 billion neurons
267
608398
1600
Gure 86 mila milioi neuronekin
10:21
and 60 to 70 kilos of body mass,
268
609998
3035
eta gure 60-70 kg-ko gorputzekin,
10:25
we should have to spend over nine hours
269
613033
3561
egunean 9 ordu baino gehiago
pasa beharko genituzke
egunero gure elikadura beharrak asetzen,
10:28
per day every single day feeding,
270
616594
3575
10:32
which is just not feasible.
271
620169
2039
eta hau ezinezkoa da.
10:34
If we ate like a primate,
272
622208
1834
Primateek bezala jango bagenu,
10:36
we should not be here.
273
624042
2253
ez ginateke hemen egongo.
10:38
How did we get here, then?
274
626295
2127
Orduan, nola heldu ginen hona?
10:40
Well, if our brain costs just as much energy
275
628422
2735
Gure garunak
hainbeste energia erabiltzen badu,
10:43
as it should, and if we can't spend
276
631157
1723
eta ezin badugu jaten eman
esna gauden ordu bakoitza,
10:44
every waking hour of the day feeding,
277
632880
3674
10:48
then the only alternative, really,
278
636554
1911
dugun aukera bakarra
10:50
is to somehow get more energy
279
638465
1958
alimentu berdinetatik
10:52
out of the same foods.
280
640423
1953
energia gehiago lortzea da.
10:54
And remarkably, that matches exactly
281
642376
3800
Harrigarria badirudi ere, hori bat dator
10:58
what our ancestors are believed to have invented
282
646176
3037
duela milioi eta erdi urte
11:01
one and a half million years ago,
283
649213
1839
gure arbasoek asmatu zutela
uste denarekin,
11:03
when they invented cooking.
284
651052
2782
janaria prestatzearekin alegia.
11:05
To cook is to use fire
285
653834
1970
Janaria prestatzea sua erabiliz
11:07
to pre-digest foods outside of your body.
286
655804
3800
elikagaiak gorputzetik kanpo
aurrez liseritzea da.
11:11
Cooked foods are softer, so they're easier to chew
287
659604
2606
Elikagai egosiak leunagoak dira,
murtxikatzeko errazagoak
11:14
and to turn completely into mush in your mouth,
288
662210
2563
eta errazago bihurtzen dira papila ahoan.
11:16
so that allows them to be completely digested
289
664773
2152
Horrela estomagoan erabat liseritu
11:18
and absorbed in your gut,
290
666925
1436
eta xurgatzen dira.
11:20
which makes them yield much more
energy in much less time.
291
668361
3655
Honela, denbora gutxiagoan
energia gehiago sor dezakegu.
Beraz, janaria prestatzeak
11:24
So cooking frees time for us to do
292
672016
2489
neuronekin gauza interesgarriagoak
11:26
much more interesting things with our day
293
674505
2062
egiteko denbora ematen digu.
11:28
and with our neurons
294
676567
1480
Ez dugu etengabe janarian,
janaria biltzean eta jatean
11:30
than just thinking about food,
295
678047
1905
11:31
looking for food, and gobbling down food
296
679952
1704
pentsatu behar.
11:33
all day long.
297
681656
1225
11:34
So because of cooking, what once was
298
682881
2499
Beraz, janaria prestatzen dugulako,
behin eragozpen handi bat
izan zen garun handi hau
11:37
a major liability, this large,
299
685380
2353
neuronez beteta
eta energia gastu handia duen garun hau,
11:39
dangerously expensive brain with a lot of neurons,
300
687733
3033
oso baliagarri bihurtu da,
11:42
could now become a major asset,
301
690766
2036
neurona piloarentzako
energia lortu dezakegulako
11:44
now that we could both afford
the energy for a lot of neurons
302
692802
3251
eta eurekin gauza interesgarriak
egiteko astia izan.
11:48
and the time to do interesting things with them.
303
696056
2503
11:50
So I think this explains why the human brain
304
698559
1974
Honek azaltzen du eboluzioan zehar
11:52
grew to become so large so fast in evolution,
305
700533
3240
zergatik hain azkar hazi zen
giza garuna, handia egin arte,
11:55
all of the while remaining just a primate brain.
306
703773
3897
primate garuna
izaten jarraitzen zuen bitartean.
Janaria prestatzeak
garun handi hau eskuragarri egin
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
eta elikagai gordinetatik kulturara,
nekazaritzara, zibilizaziora, dendetara,
12:05
agriculture, civilization, grocery stores,
309
713357
2606
elektrizitatera, hozkailuetara,
12:07
electricity, refrigerators,
310
715963
1625
eta egun ditugun
gauzetara heldu gara.
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
Honela gauza gara
egun guztia iraun ahal izateko energia
12:13
for the whole day in a single sitting
313
721237
2782
janari azkarreko
gustuko lekuetan kolpetik lortzeko.
12:16
at your favorite fast food joint.
314
724019
2954
12:18
So what once was a solution
315
726973
2437
Behin konponbide bat izan zena
12:21
now became the problem,
316
729410
1699
orain arazo bihurtu da.
12:23
and ironically, we look for the solution in raw food.
317
731109
5517
Ironikoki, orain konponbidea
elikagai gordinetan bilatzen dugu.
12:28
So what is the human advantage?
318
736626
2556
Zein da gizakiaren abantaila?
12:31
What is it that we have
319
739182
1503
Zer daukagu
beste animaliek ez daukatena?
12:32
that no other animal has?
320
740685
2535
Nire erantzuna hau da: garun kortexean
12:35
My answer is that we have the largest number
321
743220
2348
neurona kopuru handiena dugu
eta uste dut hori dela
12:37
of neurons in the cerebral cortex,
322
745568
1472
12:39
and I think that's the simplest explanation
323
747040
1844
gure gaitasun kognitibo ezohikoen
azalpen sinpleena.
12:40
for our remarkable cognitive abilities.
324
748884
2013
12:42
And what is it that we do that no other animal does,
325
750897
3227
Zer egiten dugu
beste animaliek egiten ez dutena,
12:46
and which I believe was fundamental
326
754124
1969
nire ustez oinarrizkoa dena,
12:48
to allow us to reach that large,
327
756093
3083
garun kortexean ditugun
neurona kantitate izugarri horrek
12:51
largest number of neurons in the cortex?
328
759176
2222
posible egiten duena?
12:53
In two words, we cook.
329
761398
2215
Bi hitzetan: janaria prestatu.
Beste animaliarik ez dago
janaria prestatzen duenik.
12:55
No other animal cooks its food. Only humans do.
330
763613
3566
Gizakiek bakarrik egiten dute.
Horrela heldu ginen gizaki izatera.
12:59
And I think that's how we got to become human.
331
767179
2870
Giza garuna ikertzeak
elikagaiez nuen pentsaera aldatu dit.
13:02
Studying the human brain changed
the way I think about food.
332
770049
2460
13:04
I now look at my kitchen,
333
772509
1645
Orain sukaldea begiratu
eta gurtu egiten dut.
13:06
and I bow to it,
334
774154
1470
13:07
and I thank my ancestors for coming up
335
775624
1705
Arbasoei eskertzen diet
13:09
with the invention that probably made us humans.
336
777329
1900
ziurrenik gizaki egin gaituen
asmakizuna sortzeagatik.
13:11
Thank you very much.
337
779229
2132
Mila esker.
13:13
(Applause)
338
781361
6353
(Txaloak)
Translated by Jone Aliri
Reviewed by Begoña Laka

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ABOUT THE SPEAKER
Suzana Herculano-Houzel - Neuroscientist
Suzana 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.

More profile about the speaker
Suzana Herculano-Houzel | Speaker | TED.com