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

Translator: Gabi Rolih Reviewer: Snežana Stone

What is so special about the human brain?

Zakaj so človeški možgani tako posebni?

Why is it that we study other animals

Zakaj mi proučujemo druge živali

instead of them studying us?

in ne one nas?

What does a human brain have or do

Kaj imajo človeški možgani,

that no other brain does?

česar nimajo nobeni drugi?

When I became interested in these questions about 10 years ago,

Pred desetimi leti sem se začela zanimati za ta vprašanja,

scientists thought they knew what different brains were made of.

in znanstveniki so mislili, da vedo, kako so možgani sestavljeni.

Though it was based on very little evidence,

Kljub malo dokazom,

many scientists thought that all mammalian brains,

so mnogi mislili, da so možgani vseh sesalcev,

including the human brain,

vključno s človeškimi,

were made in the same way,

sestavljeni na enak način,

with a number of neurons that was always

s številom nevronov, ki je vedno

proportional to the size of the brain.

v sorazmerju z velikostjo možganov.

This means that two brains of the same size,

To pomeni, da bi dvoje enakih možganov

like these two, with a respectable 400 grams,

tako kot ti, ki tehtajo 400 gramov,

should have similar numbers of neurons.

morali imeti podobno število nevronov.

Now, if neurons are the functional

Torej, če so nevroni funkcionalne enote možganov,

information processing units of the brain,

ki obdelujejo informacije,

then the owners of these two brains

bi morala imeti lastnika teh možganov

should have similar cognitive abilities.

podobne kognitivne zmožnosti.

And yet, one is a chimp,

Toda en je šimpanz,

and the other is a cow.

drugi pa krava.

Now maybe cows have a really rich

No, mogoče imajo krave

internal mental life and are so smart

zelo živahno miselno življenje in so tako pametne,

that they choose not to let us realize it,

da to pred nami skrivajo,

but we eat them.

toda jemo jih.

I think most people will agree

Mislim, da se bo večina strinjala,

that chimps are capable of much more complex,

da so šimpanzi zmožni dosti bolj zapletenega,

elaborate and flexible behaviors than cows are.

izpiljenega in prilagodljivega obnašanja kot krave.

So this is a first indication that the

To je torej prvi kazalec, da trditev

"all brains are made the same way" scenario

"vsi možgani so sestavljeni enako"

is not quite right.

ni čisto pravilna.

But let's play along.

Ampak vseeno se poigrajmo z njo.

If all brains were made the same way

Če bi bili vsi možgani enaki

and you were to compare animals with brains of different sizes,

in mi bi primerjali živali z možgani različnih velikosti,

larger brains should always have more neurons

bi večji možgani vedno morali imeti več nevronov

than smaller brains, and the larger the brain,

kot manjši možgani in večji kot bi možgani bili,

the more cognitively able its owner should be.

bolj kognitivno sposoben bi moral biti njihov lastnik.

So the largest brain around should also be

Torej bi morali biti največji možgani

the most cognitively able.

tudi najbolj sposobni.

And here comes the bad news:

Toda tu je slaba novica:

Our brain, not the largest one around.

Naši možgani niso največji naokrog.

It seems quite vexing.

V bistvu je kar razburljivo.

Our brain weighs between 1.2 and 1.5 kilos,

Naši možgani tehtajo med 1,2 in 1,5 kilograma,

but elephant brains weigh between four and five kilos,

slonovi možgani med 4 in 5 kilogrami

and whale brains can weigh up to nine kilos,

in kitovi možgani tudi do 9 kilogramov,

which is why scientists used to resort to saying

zato so se znanstveniki zatekali k trditvi,

that our brain must be special

da so naši možgani nekaj posebnega.

to explain our cognitive abilities.

Tako so lahko razložili naše kognitivne zmožnosti.

It must be really extraordinary,

Naši možgani morajo biti res nekaj izrednega,

an exception to the rule.

neka izjema k pravilu.

Theirs may be bigger, but ours is better,

Njihovi možgani so morda večji, toda naši so boljši

and it could be better, for example,

in bi bili boljši na primer v tem,

in that it seems larger than it should be,

da se zdijo večji kot bi morali biti,

with a much larger cerebral cortex than we should have

z dosti večjo površino možganske skorje kot pričakovano

for the size of our bodies.

glede na velikost našega telesa.

So that would give us extra cortex

Tako bi imeli več skorje,

to do more interesting things than just operating the body.

da bi lahko počeli bolj zanimive stvari kot pa le upravljali telo.

That's because the size of the brain

To je zato, ker velikost možganov

usually follows the size of the body.

navadno sledi velikosti telesa.

So the main reason for saying that

Glavni razlog za trditev,

our brain is larger than it should be

da so naši možgani večji kot bi morali biti,

actually comes from comparing ourselves

v bistvu izhaja iz primerjave ljudi

to great apes.

z velikimi opicami.

Gorillas can be two to three times larger than we are,

Gorile so lahko tudi do trikrat večje od nas,

so their brains should also be larger than ours,

torej bi njihovi možgani morali biti večji kot naši,

but instead it's the other way around.

v bistvu pa je ravno nasprotno.

Our brain is three times larger than a gorilla brain.

Naši možgani so trikrat večji od gorilinih.

The human brain also seems special

Človeški možgani so tudi posebni,

in the amount of energy that it uses.

kar se tiče porabe energije.

Although it weighs only two percent of the body,

Čeprav možgani tehtajo le dva odstotka telesa,

it alone uses 25 percent of all the energy

porabijo 25 odstotkov celotne energije,

that your body requires to run per day.

ki jo naše telo na dan potrebuje.

That's 500 calories out of a total of 2,000 calories,

To pomeni 500 od skupaj 2.000 kalorij

just to keep your brain working.

samo za delovanje naših možganov.

So the human brain is larger than it should be,

Človeški možgani so večji, kot bi morali biti,

it uses much more energy than it should,

porabijo več energije, kot bi jo morali,

so it's special.

torej so posebni.

And this is where the story started to bother me.

Tu pa me je nekaj zmotilo.

In biology, we look for rules

V biologiji iščemo pravila,

that apply to all animals and to life in general,

ki se nanašajo na živali in življenje na splošno,

so why should the rules of evolution

zakaj bi torej morala pravila evolucije

apply to everybody else but not to us?

veljati za vse, le za nas ne?

Maybe the problem was with the basic assumption

Mogoče je problem v tem, da je osnovna trditev,

that all brains are made in the same way.

da so vsi možgani sestavljeni enako.

Maybe two brains of a similar size

Morda so dvoji podobno težki možgani

can actually be made of very different numbers of neurons.

sestavljeni iz zelo različnega števila nevronov.

Maybe a very large brain

Morda veliki možgani

does not necessarily have more neurons

nimajo nujno več nevronov

than a more modest-sized brain.

kot možgani bolj skromne velikosti.

Maybe the human brain actually has the most neurons

Mogoče imajo človeški možgani največ nevronov

of any brain, regardless of its size,

od vseh možganov, ne glede na njihovo velikost,

especially in the cerebral cortex.

še posebej v možganski skorji.

So this to me became

Zame je to postalo

the important question to answer:

najpomembnejše vprašanje:

how many neurons does the human brain have,

Koliko nevronov imajo človeški možgani

and how does that compare to other animals?

in kako je to število primerljivo z drugimi živalmi?

Now, you may have heard or read somewhere

Mogoče ste kje že slišali ali prebrali,

that we have 100 billion neurons,

da imamo 100 milijard nevronov,

so 10 years ago, I asked my colleagues

zato sem pred desetimi leti svoje kolege vprašala,

if they knew where this number came from.

ali vedo, od kod izhaja to število.

But nobody did.

A nihče ni vedel.

I've been digging through the literature

Brskala sem po literaturi,

for the original reference for that number,

da bi našla izvirno omembo tega števila,

and I could never find it.

a je nikoli nisem našla.

It seems that nobody had actually ever counted

Zdi se, da v bistvu še nihče ni štel

the number of neurons in the human brain,

nevronov v človeških možganih,

or in any other brain for that matter.

pravzaprav še v nobenih možganih.

So I came up with my own way to count cells in the brain,

Zato sem iznašla svoj način štetja celic v možganih,

and it essentially consists of

in sicer možgane raztapljam v juho.

dissolving that brain into soup.

It works like this:

Tako deluje:

You take a brain, or parts of that brain,

Vzamemo možgane ali dele možganov

and you dissolve it in detergent,

in jih raztopimo v detergentu,

which destroys the cell membranes

ki uniči celično membrano,

but keeps the cell nuclei intact,

jedro pa pusti nedotaknjeno,

so you end up with a suspension of free nuclei

tako da dobimo suspenzijo prostih jeder,

that looks like this,

ki izgleda takole -

like a clear soup.

kot bistra juha.

This soup contains all the nuclei

Juha vsebuje vsa jedra,

that once were a mouse brain.

ki so nekoč bila mišji možgani.

Now, the beauty of a soup is that because it is soup,

No, prednost juhe je, da jo lahko premešamo

you can agitate it and make those nuclei

in vsa jedra se homogeno

be distributed homogeneously in the liquid,

razporedijo v tekočini,

so that now by looking under the microscope

zato da lahko zdaj pod mikroskopom

at just four or five samples of this homogeneous solution,

v le štirih ali petih vzorcih te homogene raztopine

you can count nuclei, and therefore tell

preštejemo jedra

in tako vemo, koliko celic so imeli ti možgani.

how many cells that brain had.

It's simple, it's straightforward,

To je preprost

and it's really fast.

in tudi hiter postopek.

So we've used that method to count neurons

To metodo smo uporabili za štetje nevronov

in dozens of different species so far,

pri ducatih različnih vrst do sedaj.

and it turns out that all brains

Izkazalo se je, da vsi možgani

are not made the same way.

niso sestavljeni enako.

Take rodents and primates, for instance:

Vzemimo na primer glodavce in primate:

In larger rodent brains, the average size

V večjih možganih glodavcev

of the neuron increases,

se povprečna velikost nevronov povečuje,

so the brain inflates very rapidly

zato se možgani hitro napihnejo

and gains size much faster than it gains neurons.

in pridobijo na velikosti dosti hitreje kot na nevronih.

But primate brains gain neurons

Primati pa dobijo nevrone

without the average neuron becoming any larger,

ne da bi se povprečni nevroni povečali,

which is a very economical way

kar je zelo ekonomičen način

to add neurons to your brain.

dodajanja nevronov k možganom.

The result is that a primate brain

Rezultat tega je, da imajo možgani primatov

will always have more neurons than a rodent brain of the same size,

več nevronov kot možgani glodavcev iste velikosti

and the larger the brain,

in večji kot so možgani,

the larger this difference will be.

večja bo razlika.

Well, what about our brain then?

Kako je torej z našimi možgani?

We found that we have, on average,

Odkrili smo, da imamo v povprečju

86 billion neurons,

86 milijard nevronov,

16 billion of which are in the cerebral cortex,

od katerih je 16 milijard v možganski skorji.

and if you consider that the cerebral cortex

Če upoštevate, da je možganska skorja

is the seat of functions like

središče funkcij, kot so zavedanje

awareness and logical and abstract reasoning,

ter logično in abstraktno mišljenje,

and that 16 billion is the most neurons

in da je 16 milijard največ nevronov

that any cortex has,

v kateri koli možganski skorji,

I think this is the simplest explanation

je po moje to najenostavnejša razlaga

for our remarkable cognitive abilities.

za naše izredne kognitivne zmožnosti.

But just as important is what the 86 billion neurons mean.

Toda prav tako je pomembno, kaj teh 86 milijard nevronov pomeni.

Because we found that the relationship

Ker smo odkrili, da lahko razmerje

between the size of the brain and its number of neurons

med velikostjo možganov in številom njihovih nevronov

could be described mathematically,

opišemo z matematičnimi odnosi,

we could calculate what a human brain

smo lahko izračunali, kakšni bi bili človeški možgani,

would look like if it was made like a rodent brain.

če bi bili zgrajeni kot možgani glodavcev.

So, a rodent brain with 86 billion neurons

Možgani glodavcev s 86 milijardami nevronov

would weigh 36 kilos.

bi tehtali 36 kilogramov.

That's not possible.

To ni možno.

A brain that huge would be crushed

Tako velike možgane bi uničila

by its own weight,

njihova lastna teža

and this impossible brain would go

in ti možgani bi bili

in the body of 89 tons.

v telesu, ki tehta 89 ton.

I don't think it looks like us.

To ne izgleda ravno kot mi.

So this brings us to a very important conclusion already,

To nas privede do že zelo pomembnega zaključka,

which is that we are not rodents.

in sicer, da nismo glodavci.

The human brain is not a large rat brain.

Človeški možgani niso veliki možgani podgane.

Compared to a rat, we might seem special, yes,

V primerjavi s podgano seveda izgledamo posebni,

but that's not a fair comparison to make,

toda ta primerjava ni pravična,

given that we know that we are not rodents.

saj vemo, da nismo glodavci.

We are primates,

Primati smo,

so the correct comparison is to other primates.

torej je bolj pravilna primerjava z drugimi primati.

And there, if you do the math,

In če tu vse izračunate,

you find that a generic primate

boste odkrili, da bi povprečni primat

with 86 billion neurons

s 86 milijardami nevronov

would have a brain of about 1.2 kilos,

imel možgane, ki bi tehtali okrog 1,2 kilograma,

which seems just right,

kar se zdi ravno prav

in a body of some 66 kilos,

za telo s približno 66-imi kilogrami,

which in my case is exactly right,

kar velja ravno zame,

which brings us to a very unsurprising

kar nas pripelje do nepresenetljivega,

but still incredibly important conclusion:

toda izredno pomembnega zaključka:

I am a primate.

Primat sem.

And all of you are primates.

In tudi vi ste primati.

And so was Darwin.

In tudi Darwin je bil.

I love to think that Darwin would have really appreciated this.

Rada si mislim, da bi Darwin zelo cenil te zaključke.

His brain, like ours,

Njegovi možgani, tako kot naši,

was made in the image of other primate brains.

so bili narejeni po zgledu drugih primatov.

So the human brain may be remarkable, yes,

Človeški možgani so gotovo neverjetni,

but it is not special in its number of neurons.

toda naše število nevronov ni nič posebnega.

It is just a large primate brain.

Imamo le velike možgane primatov.

I think that's a very humbling and sobering thought

Mislim, da nas lahko ta misel strezni in nas naredi bolj ponižne

that should remind us of our place in nature.

ter nas spomni na naše mesto v naravi.

Why does it cost so much energy, then?

Zakaj nas potem možgani stanejo toliko energije?

Well, other people have figured out

Drugi ljudje so ugotovili,

how much energy the human brain

koliko porabijo človeški možgani

and that of other species costs,

in koliko možgani drugih vrst.

and now that we knew how many neurons

Ko smo izvedeli, koliko nevronov je v možganih, smo naredili izračun.

each brain was made of, we could do the math.

And it turns out that both human

Izkazalo se je, da tako človeški možgani

and other brains cost about the same,

kot možgani drugih vrst porabijo skoraj enako,

an average of six calories per billion neurons per day.

v povprečju 6 kalorij na milijardo nevronov na dan.

So the total energetic cost of a brain

Skupna energijska poraba možganov

is a simple, linear function

je preprosta linearna funkcija

of its number of neurons,

števila njihovih nevronov

and it turns out that the human brain

in izkazalo se je, da človeški možgani

costs just as much energy as you would expect.

porabijo prav toliko energije, kot bi pričakovali.

So the reason why the human brain

Razlog, da človeški možgani

costs so much energy is simply because

porabijo toliko energije,

it has a huge number of neurons,

je v tem, da imajo veliko število nevronov.

and because we are primates

Ker smo primati

with many more neurons for a given body size

z dosti več nevroni glede na velikost telesa

than any other animal,

kot katerakoli druga žival,

the relative cost of our brain is large,

je tudi povprečna poraba možganov velika,

but just because we're primates, not because we're special.

toda le zato, ker smo primati, in ne, ker smo posebni.

Last question, then:

Še zadnje vprašanje:

how did we come by this remarkable number of neurons,

Kako smo prišli do tega izrednega števila nevronov,

and in particular, if great apes

in natančneje, če so velike opice

are larger than we are,

večje od nas,

why don't they have a larger brain than we do, with more neurons?

zakaj nimajo večjih možganov, z več nevroni?

When we realized how much expensive it is

Ko smo se zavedli, kako drago je

to have a lot of neurons in the brain, I figured,

imeti veliko nevronov v možganih, sem sklepala,

maybe there's a simple reason.

da mogoče za to obstaja preprost razlog.

They just can't afford the energy

Opice si ne morejo privoščiti energije

for both a large body and a large number of neurons.

za veliko telo in za veliko število nevronov.

So we did the math.

Zato smo se lotili računanja.

We calculated on the one hand

Izračunali smo,

how much energy a primate gets per day

koliko energije primati dobijo na dan

from eating raw foods,

s surovo hrano,

and on the other hand, how much energy

koliko energije porabi

a body of a certain size costs

telo določene velikosti

and how much energy a brain of a certain number of neurons costs,

in koliko energije porabijo možgani z določenim številom nevronov.

and we looked for the combinations

Iskali smo kombinacije

of body size and number of brain neurons

velikosti telesa in števila nevronov,

that a primate could afford

ki bi si jih primati lahko privoščili,

if it ate a certain number of hours per day.

če bi določeno število ur dnevno porabili za prehrano.

And what we found is that

Ugotovili smo,

because neurons are so expensive,

da ker so nevroni tako dragi,

there is a tradeoff between body size and number of neurons.

obstaja kompromis med velikostjo telesa in številom nevronov.

So a primate that eats eight hours per day

Primati, ki se prehranjujejo osem ur na dan,

can afford at most 53 billion neurons,

si lahko privoščijo 53 milijard nevronov,

but then its body cannot be any bigger

toda potem njihovo telo ne more presegati

than 25 kilos.

25 kilogramov teže.

To weigh any more than that,

Če bi tehtali več,

it has to give up neurons.

bi se morali odpovedati nevronom.

So it's either a large body

Imamo lahko torej veliko telo

or a large number of neurons.

ali pa veliko število nevronov.

When you eat like a primate,

Če jemo kot primati,

you can't afford both.

si drugega ne moremo privoščiti.

One way out of this metabolic limitation

En izhod iz te metabolične omejitve bi bil

would be to spend even more hours per day eating,

porabiti še več ur na dan za prehranjevanje,

but that gets dangerous,

toda to postane nevarno

and past a certain point, it's just not possible.

in od neke točke ni več možno.

Gorillas and orangutans, for instance,

Gorile in orangutani

afford about 30 billion neurons

si na primer lahko privoščijo 30 milijard nevronov

by spending eight and a half hours per day eating,

s prehranjevanjem 8 in pol ur na dan,

and that seems to be about as much as they can do.

kar se zdi največ kar lahko naredijo.

Nine hours of feeding per day

Devet ur na dan za hranjenje

seems to be the practical limit for a primate.

se zdi stvarna omejitev za primate.

What about us?

Kaj pa mi?

With our 86 billion neurons

S 86 milijardami nevronov

and 60 to 70 kilos of body mass,

in 60 do 70 kilogramov telesne mase

we should have to spend over nine hours

bi morali preživeti več kot 9 ur na dan

per day every single day feeding,

za prehranjevanje,

which is just not feasible.

kar preprosto ni uresničljivo.

If we ate like a primate,

Če bi jedli kot primati,

we should not be here.

nas ne bi bilo.

How did we get here, then?

Kako smo potem prišli sem?

Well, if our brain costs just as much energy

Če nas možgani stanejo toliko energije,

as it should, and if we can't spend

kot bi nas morali in če ne moremo preživeti

every waking hour of the day feeding,

vsake sleherne ure za hranjenje,

then the only alternative, really,

potem je edina alternativa

is to somehow get more energy

dobiti več energije

out of the same foods.

iz enake hrane.

And remarkably, that matches exactly

In neverjetno, o se pravzaprav ujema s tem,

what our ancestors are believed to have invented

kar so naši predniki najverjetneje izumili

one and a half million years ago,

pred enim in pol milijonom let,

when they invented cooking.

ko so izumili kuhanje.

To cook is to use fire

Kuhati pomeni uporabiti ogenj,

to pre-digest foods outside of your body.

da predhodno predelamo hrano preden ta vstopi v naše telo.

Cooked foods are softer, so they're easier to chew

Kuhana hrana je mehkejša, torej tudi lažja za žvečenje

and to turn completely into mush in your mouth,

in se v naših ustih lažje spremeni v kašo,

so that allows them to be completely digested

kar hrani dovoli, da je popolnoma presnovljena

and absorbed in your gut,

in se absorbira v naše črevo,

which makes them yield much more energy in much less time.

zaradi česar pridobimo več energije v krajšem času.

So cooking frees time for us to do

Zaradi kuhanja pridobimo čas,

much more interesting things with our day

da svoj dan in svoje nevrone

and with our neurons

porabimo za kaj bolj zanimivega,

than just thinking about food,

kot da le mislimo na hrano,

looking for food, and gobbling down food

iščemo hrano in goltamo hrano

all day long.

ves ljubi dan.

So because of cooking, what once was

Zaradi kuhanja

a major liability, this large,

je nekdanja omejitev, ti ogromni,

dangerously expensive brain with a lot of neurons,

nevarno dragi možgani z veliko nevroni,

could now become a major asset,

postala ogromna prednost.

now that we could both afford the energy for a lot of neurons

Zdaj si lahko privoščimo tako energijo za dosti nevronov

and the time to do interesting things with them.

kot tudi čas, da z njimi delamo zanimive reči.

So I think this explains why the human brain

Zato mislim, da to razloži, zakaj so človeški možgani

grew to become so large so fast in evolution,

postali tako veliki tako hitro v evoluciji,

all of the while remaining just a primate brain.

medtem ko so še vedno le možgani primatov.

With this large brain now affordable by cooking,

Ker si zaradi kuhanja zdaj lahko privoščimo tako velike možgane,

we went rapidly from raw foods to culture,

smo hitro prešli s surove prehrane na kulturo,

agriculture, civilization, grocery stores,

kmetijstvo, civilizacijo, trgovine,

electricity, refrigerators,

elektriko, hladilnike,

all of those things that nowadays

vse te reči, ki nam danes dovoljujejo

allow us to get all the energy we need

da dobimo energijo, potrebno za celotni dan,

for the whole day in a single sitting

le z enim obiskom

at your favorite fast food joint.

svojega najljubšega kotička s hitro hrano.

So what once was a solution

Kar je nekoč predstavljalo rešitev,

now became the problem,

je danes postalo problem

and ironically, we look for the solution in raw food.

in ironično sami rešitev iščemo v surovi prehrani.

So what is the human advantage?

Kaj pa je prednost ljudi?

What is it that we have

Kaj imamo,

that no other animal has?

česar nima nobena druga žival?

My answer is that we have the largest number

Moj odgovor je, da imamo največje število

of neurons in the cerebral cortex,

nevronov v možganski skorji

and I think that's the simplest explanation

in po moje je to najlažja razlaga

for our remarkable cognitive abilities.

za naše izjemne kognitivne sposobnosti.

And what is it that we do that no other animal does,

In kaj mi delamo, česar nobena druga žival ne počne,

and which I believe was fundamental

in kar je postavilo temelje,

to allow us to reach that large,

da smo lahko dosegli tako veliko,

largest number of neurons in the cortex?

največje število nevronov v možganski skorji?

In two words, we cook.

Z eno besedo - kuhamo.

No other animal cooks its food. Only humans do.

Nobena druga žival si ne kuha hrane. Le ljudje si jo.

And I think that's how we got to become human.

In mislim, da smo zaradi tega lahko postali ljudje.

Pri proučevanju človeških možganov sem o hrani začela drugače razmišljati.

Studying the human brain changed the way I think about food.

I now look at my kitchen,

Zdaj pogledam svojo kuhinjo,

and I bow to it,

se ji priklonim

and I thank my ancestors for coming up

in se zahvalim svojim prednikom za izum tega,

with the invention that probably made us humans.

kar nas je verjetno naredilo človeške.

Thank you very much.

Hvala lepa.

(Applause)

(Aplavz)