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: 2013-06-12

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.

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

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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394157

2553

Guzti honek
ondorio nagusi batera garamatza:

06:48

which is that we are not rodents.

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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

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

THE ORIGINAL VIDEO ON TED.COM

Suzana Herculano-Houzel: Zer du hain berezia giza garunak? | TED Talk | TED.com