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

Prevoditelj: Senzos Osijek Recezent: Ivan Stamenković

What is so special about the human brain?

Što je tako posebno oko ljudskog mozga?

Why is it that we study other animals

Zašto smo mi ti koji proučavamo druge životinje,

instead of them studying us?

a ne one nas?

What does a human brain have or do

Što to ljudski mozak ima ili radi

that no other brain does?

što nijedan drugi mozak ne radi?

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

Kada sam se počela zanimati za ova pitanja prije 10 godina,

scientists thought they knew what different brains were made of.

znanstvenici su mislili da znaju od čega su sačinjeni različiti mozgovi.

Though it was based on very little evidence,

Iako je postojalo vrlo malo dokaza,

many scientists thought that all mammalian brains,

mnogi znanstvenici su mislili da je mozak sisavaca,

including the human brain,

uključujući i ljudski mozak,

were made in the same way,

sačinjen na isti način,

with a number of neurons that was always

s brojem neurona koji su uvijek

proportional to the size of the brain.

proporcionalni veličini mozga.

This means that two brains of the same size,

To znači da dva mozga jednake veličine,

like these two, with a respectable 400 grams,

poput ova dva, s dobranih 400 grama,

should have similar numbers of neurons.

bi trebali imati sličan broj neurona.

Now, if neurons are the functional

Sad, ako su neuroni funkcionalna

information processing units of the brain,

jedinica mozga koja procesuira informacije,

then the owners of these two brains

tada bi vlasnici ovih mozgova

should have similar cognitive abilities.

trebali imati slične kognitivne sposobnosti.

And yet, one is a chimp,

A ipak, jedna je čimpanza,

and the other is a cow.

a druga je krava.

Now maybe cows have a really rich

Sad, moguće je da krave imaju vrlo bogat

internal mental life and are so smart

unutarnji mentalni život i da su toliko pametne

that they choose not to let us realize it,

da nam ne dopuštaju da to vidimo,

but we eat them.

ali mi ih jedemo.

I think most people will agree

Mislim da će se većina ljudi složiti

that chimps are capable of much more complex,

da su čimpanze sposobne za mnogo složenije,

elaborate and flexible behaviors than cows are.

planirano i fleksibilno ponašanje nego krave.

So this is a first indication that the

To je prvi pokazatelj da

"all brains are made the same way" scenario

„svi su mozgovi sačinjeni na isti način“ scenarij

is not quite right.

nije sasvim točan.

But let's play along.

Ali hajdemo se zabaviti.

If all brains were made the same way

Ako su svi mozgovi sačinjeni na isti način

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

i ako ćemo uspoređivati životinje s mozgovima različitih veličina,

larger brains should always have more neurons

veći mozgovi bi uvijek trebali imati više neurona

than smaller brains, and the larger the brain,

no mali mozgovi, i što je veći mozak,

the more cognitively able its owner should be.

veće su kognitivne sposobnosti njegovog vlasnika.

So the largest brain around should also be

Znači najveći mozak koji postoji bi trebao

the most cognitively able.

biti kognitivno najsposobniji.

And here comes the bad news:

I ovdje dolaze loše vijesti:

Our brain, not the largest one around.

Naš mozak nije najveći.

It seems quite vexing.

To je poprilično zbunjujuće.

Our brain weighs between 1.2 and 1.5 kilos,

Naš mozak teži između 1.2 i 1.5 kila,

but elephant brains weigh between four and five kilos,

ali mozak slona teži između četiri i pet kila,

and whale brains can weigh up to nine kilos,

a mozak kitova može težiti i devet kila

which is why scientists used to resort to saying

zbog čega znanstvenici sa sigurnošću tvrde

that our brain must be special

da je naš mozak poseban

to explain our cognitive abilities.

kako bi objasnili naše kognitivne sposobnosti.

It must be really extraordinary,

Stvarno mora biti izvanredan,

an exception to the rule.

iznimka pravilu.

Theirs may be bigger, but ours is better,

Možda je njihov veći, ali naš je bolji,

and it could be better, for example,

i mogao bi biti bolji, na primijer,

in that it seems larger than it should be,

u tome što se čini većim no što je,

with a much larger cerebral cortex than we should have

s mnogo većom moždanom korom no što bi trebali imati

for the size of our bodies.

Za veličinu našeg tijela.

So that would give us extra cortex

To bi nam dalo dodatne kore

to do more interesting things than just operating the body.

kako bi smo radili zanimljivije stvari nego samo upravljali tijelom.

That's because the size of the brain

To je zato jer veličina mozga

usually follows the size of the body.

obično prati veličinu tijela.

So the main reason for saying that

Zato je glavni razlog za tvrdnju da

our brain is larger than it should be

je naš mozak veći no što bi trebao biti

actually comes from comparing ourselves

zapravo dolazi od usporedbe nas

to great apes.

s velikim primatima.

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

Gorile mogu biti dva do tri puta veće od nas,

so their brains should also be larger than ours,

pa bi i njihovi mozgovi također trebali biti veći od naših,

but instead it's the other way around.

ali zapravo je obrnuto.

Our brain is three times larger than a gorilla brain.

Naš mozak je tri puta veći od mozga gorile.

The human brain also seems special

Ljudski mozak je također poseban

in the amount of energy that it uses.

po količini energije koju koristi.

Although it weighs only two percent of the body,

Iako teži samo 2% našeg tijela,

it alone uses 25 percent of all the energy

sam koristi 25% cjeloukupne energije

that your body requires to run per day.

koje naše tijelo treba u jednom danu.

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

To je otprilike 500 kalorija od sveukupnih 2000 kalorija,

just to keep your brain working.

samo kako bi vam mozak radio.

So the human brain is larger than it should be,

Znači ljudski mozak je veći no što bi trebao biti,

it uses much more energy than it should,

koristi puno više energije no što bi trebao,

so it's special.

pa je poseban.

And this is where the story started to bother me.

I ovdje me je priča počela mučiti.

In biology, we look for rules

U biologiji tražimo zakone

that apply to all animals and to life in general,

koji su primjenjivi na sve životinje i život generalno,

so why should the rules of evolution

pa zašto bi zakoni evolucije

apply to everybody else but not to us?

bili primjenjivi na sve osim nas?

Maybe the problem was with the basic assumption

Možda je problem sa osnovnom pretpostavkom

that all brains are made in the same way.

da su svi mozgovi sačinjeni jednako.

Maybe two brains of a similar size

Možda dva mozga slične veličine

can actually be made of very different numbers of neurons.

mogu zapravo biti sačinjeni od različitog broja neurona.

Maybe a very large brain

Možda veoma velik mozak

does not necessarily have more neurons

ne mora nužno imati više neurona

than a more modest-sized brain.

od nekog mozga umjerene veličine.

Maybe the human brain actually has the most neurons

Možda ljudski mozak zapravo ima najvišen neurona

of any brain, regardless of its size,

nego bilo koji mozak, neovisno o njegovoj veličini,

especially in the cerebral cortex.

posebno u moždanoj kori.

So this to me became

To mi je postalo

the important question to answer:

važno pitanje za odgovoriti:

how many neurons does the human brain have,

koliko neurona ima ljudski mozak,

and how does that compare to other animals?

i kako to izgleda u usporedbi s drugim životinjama?

Now, you may have heard or read somewhere

Sad, možda ste čuli ili pročitali negdje

that we have 100 billion neurons,

da imamo 100 milijardi neurona,

so 10 years ago, I asked my colleagues

i prije 10 godina, pitala sam svoje kolege

if they knew where this number came from.

znaju li odakle je došao taj broj.

But nobody did.

Nitko nije znao.

I've been digging through the literature

Kopala sam po literaturi

for the original reference for that number,

kako bi pronašla originalnu referencu na taj broj,

and I could never find it.

i nisam ju mogla pronaći.

It seems that nobody had actually ever counted

Izgleda da nitko nije zapravo prebrojao

the number of neurons in the human brain,

broj neurona u ljudskom mozgu,

or in any other brain for that matter.

ili u bilo kojem drugom mozgu zapravo.

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

Pa sam pronašla svoj način kako prebrojati stanice u mozgu,

and it essentially consists of

a zapravo se sastoji od

dissolving that brain into soup.

otapanja mozga u juhu.

It works like this:

Ovako nekako ide:

You take a brain, or parts of that brain,

Uzmete mozak, ili dijelove mozga,

and you dissolve it in detergent,

i otopite ih u deterdžentu,

which destroys the cell membranes

što uništi membrane stanica

but keeps the cell nuclei intact,

ali ostavi stanične jezgre netaknutima,

so you end up with a suspension of free nuclei

pa dobijete otopinu slobodnih jezgara

that looks like this,

koje izgledaju ovako,

like a clear soup.

poput čiste juhe.

This soup contains all the nuclei

Ova juha sadrži sve jezgre

that once were a mouse brain.

koje su bile mišji mozak.

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

Sad, ljepota ove juhe je to što je to juha,

you can agitate it and make those nuclei

možete ju izmućkati i sve te jezgre

be distributed homogeneously in the liquid,

homogeno raspršiti u tekućini,

so that now by looking under the microscope

tako da ako gledamo ispod mikroskopa

at just four or five samples of this homogeneous solution,

samo četiri ili pet uzoraka

you can count nuclei, and therefore tell

možete prebrojati jezgre, a time i saznati

how many cells that brain had.

koliko mnogo stanica postoji u mozgu.

It's simple, it's straightforward,

Jednostavno je, direktno,

and it's really fast.

i stvarno brzo.

So we've used that method to count neurons

Koristili smo ovu metodu kako bi izbrojali neurone

in dozens of different species so far,

u nekoliko različitih vrsta zasad,

and it turns out that all brains

i pokazalo se da svi mozgovi

are not made the same way.

nisu sačinjeni jednako.

Take rodents and primates, for instance:

Uzmite glodavce i primate, na primjer:

In larger rodent brains, the average size

U najvećem mozgu glodavca, prosječan broj

of the neuron increases,

neurona raste,

so the brain inflates very rapidly

tako da mozak širi jako brzo

and gains size much faster than it gains neurons.

i raste puno brže no što dobija neurone.

But primate brains gain neurons

Ali mozgovi primata dobijaju neurone

without the average neuron becoming any larger,

bez da prosječan neuron postaje veći,

which is a very economical way

što je jako ekonomičan način

to add neurons to your brain.

dodavanja neurona u mozak.

The result is that a primate brain

Rezultat je to da će mozak primata

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

uvijek imati više neurona nego mozak glodavca iste veličine,

and the larger the brain,

i što je veći mozak,

the larger this difference will be.

veća će razlika biti.

Well, what about our brain then?

A što je s našim mozgovima?

We found that we have, on average,

Saznali smo da imamo, prosječno,

86 billion neurons,

oko 89 milijardi neurona,

16 billion of which are in the cerebral cortex,

od toga 16 milijardi su u moždanoj kori,

and if you consider that the cerebral cortex

i ako uzmete u obzir to da je moždana kora

is the seat of functions like

sjedište funkcija poput

awareness and logical and abstract reasoning,

pažnje, logičnog i apstraktnog razmišljanja,

and that 16 billion is the most neurons

i da je 16 milijardi najviše neurona

that any cortex has,

što ikoja moždana kora ima,

I think this is the simplest explanation

mislim da je to najjednostavnije objašnjenje

for our remarkable cognitive abilities.

naših izvanrednih kognitivnih sposobnosti.

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

Ali jednako važno je i to što 86 milijardni neurona znači.

Because we found that the relationship

Jer saznali smo da se veza

between the size of the brain and its number of neurons

između veličine mozga i broja njegovih neurona

could be described mathematically,

može matematički objasniti,

we could calculate what a human brain

možemo izračunati kako bi

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

ljudski mozak izgledao da je sačinjen kao mozak glodavaca.

So, a rodent brain with 86 billion neurons

Mozak glodavca sa 86 milijardi neurona

would weigh 36 kilos.

težio bi 36 kila.

That's not possible.

To nije moguće.

A brain that huge would be crushed

Tako veliki mozak bi se urušio

by its own weight,

zbog svoje težine,

and this impossible brain would go

i ovakav nemoguć mozak bi morao

in the body of 89 tons.

biti u tijelu od 89 tona.

I don't think it looks like us.

Mislim da to ne izgleda kao mi.

So this brings us to a very important conclusion already,

Ovo nas već dovodi do jako važnog zaključka,

which is that we are not rodents.

a to je da nismo glodavci.

The human brain is not a large rat brain.

Ljudski mozak nije veliki mozak štakora.

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

U usporedbi sa štakorom, možda se činimo posebnima, da

but that's not a fair comparison to make,

ali to nije pošteno napravljena usporedba

given that we know that we are not rodents.

jer mi znamo da nismo glodavci.

We are primates,

Mi smo primati,

so the correct comparison is to other primates.

pa je pošteno da se uspoređujemo sa ostalim primatima

And there, if you do the math,

i ako izračunate,

you find that a generic primate

vidjeli bi da svaki primat

with 86 billion neurons

sa 86 milijardi neurona

would have a brain of about 1.2 kilos,

bi imao mozak težine otprilike 1.2 kile,

which seems just right,

što nam odgovara,

in a body of some 66 kilos,

u tijelu od nekih 66 kila,

which in my case is exactly right,

što je u mom slučaju istina,

which brings us to a very unsurprising

što nas dovodi do neiznenađujućeg

but still incredibly important conclusion:

ali ipak vrlo važnog zaključka:

I am a primate.

Ja sam primat.

And all of you are primates.

Svi ste vi primati.

And so was Darwin.

I Darwin je bio.

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

Volim misliti da bi Darwin ovo stvarno cijenio.

His brain, like ours,

Njegov mozak, poput naših,

was made in the image of other primate brains.

je sačinjen po istoj slici kao i mozak drugih primata.

So the human brain may be remarkable, yes,

Ljudski mozak je nevjerovatan, da,

but it is not special in its number of neurons.

ali nije poseban po svome broju neurona.

It is just a large primate brain.

To je samo veliki mozak primata.

I think that's a very humbling and sobering thought

Mislim da je to veoma skromno i razborito mišljenje

that should remind us of our place in nature.

koje bi nas trebalo podsjetiti na naše mjesto u prirodi.

Why does it cost so much energy, then?

Zašto onda koristi toliko energije?

Well, other people have figured out

Drugi ljudi su zapravo otkrili

how much energy the human brain

koliko energije ljudski mozak

and that of other species costs,

i mozak drugih vrsta troši,

and now that we knew how many neurons

i sada kada smo znali koliko neurona

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

svaki mozak ima, mogli smo to izračunati.

And it turns out that both human

I ispalo je da ljudski mozak

and other brains cost about the same,

i drugi mozgovi troše otprilike jednako,

an average of six calories per billion neurons per day.

prosječno šest kalorija po milijardi neurona na dan.

So the total energetic cost of a brain

Konačni utrošak energije mozga je

is a simple, linear function

jednostavno, linearna funkcija

of its number of neurons,

njegovog broja neurona,

and it turns out that the human brain

i ispalo je da ljudski mozak

costs just as much energy as you would expect.

troši onoliko energije koliko bi ste očekivali.

So the reason why the human brain

Razlog zašto ljudski mozak

costs so much energy is simply because

troši toliko energije je jednostavno jer

it has a huge number of neurons,

ima velik broj neurona,

and because we are primates

i zato što smo primati

with many more neurons for a given body size

s mnogo više neurona za našu tjelesnu veličinu

than any other animal,

nego druge životinje,

the relative cost of our brain is large,

relativni utrošak našeg mozga je velik,

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

samo zato što smo primati, ne zato što smo posebni.

Last question, then:

Posljednje pitanje, onda:

how did we come by this remarkable number of neurons,

kako smo dobili poveći broj neurona,

and in particular, if great apes

i specifično, ako su veliki primati

are larger than we are,

veći od nas,

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

zašto nemaju veće mozgove od nas, s više neurona?

When we realized how much expensive it is

Kada smo shvatili koliko bi skupo bilo

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

imati toliko neurona u mozgu, shvatila sam,

maybe there's a simple reason.

možda postoji jednostavno rješenje.

They just can't afford the energy

Jednostavno ne mogu priuštiti toliko energije

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

i za veliko tijelo i za velik broj neurona.

So we did the math.

Bavili smo se matematikom.

We calculated on the one hand

Izračunali smo u jednu ruku

how much energy a primate gets per day

koliko energije primat dobije na dan

from eating raw foods,

jedeći sirovu hranu,

and on the other hand, how much energy

i u drugu ruku, koliko energije

a body of a certain size costs

troši tijelo određene veličine,

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

i koliko energije troši mozak s određenim brojem neurona,

and we looked for the combinations

i pogledali smo kombinacije

of body size and number of brain neurons

veličine tijela i broja neurona

that a primate could afford

koje primat može priuštiti

if it ate a certain number of hours per day.

ako jede određen broj sati po danu.

And what we found is that

I otkrili smo da

because neurons are so expensive,

pošto su neuroni tako skupi,

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

postoji kompromis između tjelesne veličine i broja neurona.

So a primate that eats eight hours per day

Primati koji jedu osam sati na dan

can afford at most 53 billion neurons,

mogu priuštiti najviše 53 milijardi neurona,

but then its body cannot be any bigger

ali onda njihovo tijelo ne može biti veće

than 25 kilos.

Od 25 kila.

To weigh any more than that,

Kako bi težilo više,

it has to give up neurons.

mora se odreći neurona.

So it's either a large body

Može biti ili veliko tijelo

or a large number of neurons.

ili veliki broj neurona.

When you eat like a primate,

Kada jedete kao primat,

you can't afford both.

ne možete priuštiti oboje.

One way out of this metabolic limitation

Jedini način kako izaći iz ovog metaboličkog ograničenja

would be to spend even more hours per day eating,

je provesti još više sati na dan jedući,

but that gets dangerous,

ali ovdje priča postaje nategnuta,

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

u jednom trenutku to više neće biti moguće.

Gorillas and orangutans, for instance,

Gorile i orangutani, na primijer,

afford about 30 billion neurons

su si priuštili 30 milijardi neurona

by spending eight and a half hours per day eating,

jedući osam i pol sati na dan,

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

I to je otprilike najviše što mogu.

Nine hours of feeding per day

Devet sati hranjenja na dan

seems to be the practical limit for a primate.

izgleda da je stvarni limit za primate.

What about us?

Što je s nama?

With our 86 billion neurons

S naših 86 milijardi neurona

and 60 to 70 kilos of body mass,

i 60 do 70 kila tjelesne mase,

we should have to spend over nine hours

trebali bi provesti više od devet sati

per day every single day feeding,

po danu svaki put kada se hranimo,

which is just not feasible.

što jednostavno nije izvodljivo.

If we ate like a primate,

Ako jedemo poput primata,

we should not be here.

ne bi smo trebali biti ovdje.

How did we get here, then?

Kako smo dospjeli onda ovdje?

Well, if our brain costs just as much energy

Pa, ako naš mozak troši onoliko energije

as it should, and if we can't spend

koliko bi trebalo, i ako možemo potrošiti

every waking hour of the day feeding,

svaki budni sat u danu hraneći se,

then the only alternative, really,

onda je jedino rješenje, zapravo,

is to somehow get more energy

da nekako dobijemo više energije

out of the same foods.

iz iste hrane.

And remarkably, that matches exactly

I značajno, to odgovara upravo

what our ancestors are believed to have invented

onome što se vjeruje da su naši preci izumili

one and a half million years ago,

prije jedan i pol milijun godina,

when they invented cooking.

a to je kuhanje.

To cook is to use fire

Kuhanje je korištenje vatre

to pre-digest foods outside of your body.

kako bi se predprobavila hrana izvan našeg tijela.

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

Kuhana hrana je mekša, lakša je za žvakanje

and to turn completely into mush in your mouth,

i pretvarajući se potpuno u kašu u našim ustima,

so that allows them to be completely digested

dozvoljava joj se da bude potpuno probavljena

and absorbed in your gut,

i apsorbirana u našoj probavi,

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

što omogućava puno više energije u manje vremena.

So cooking frees time for us to do

Kuhanje nam oslobađa vrijeme kako bi radili

much more interesting things with our day

puno zanimljivije stvari s našim vremenom

and with our neurons

i s našim neuronima

than just thinking about food,

nego samo razmišljati o hrani,

looking for food, and gobbling down food

tražiti hranu i trpati ju u nas

all day long.

cijeli dan.

So because of cooking, what once was

Znači zbog kuhanja, što je prije bila

a major liability, this large,

velika prepreka, ovaj veliki,

dangerously expensive brain with a lot of neurons,

opasno skup mozak s puno neurona,

could now become a major asset,

je uspio postati od velike važnosti,

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

sad kad možemo priuštiti i energiju za mnogo neurona

and the time to do interesting things with them.

i vrijeme da radimo zanimljive stvari s njima.

So I think this explains why the human brain

Mislim da ovo objašnjava zašto je ljudski mozak

grew to become so large so fast in evolution,

postao tako velik tako brzo u evoluciji,

all of the while remaining just a primate brain.

ali i ostao samo mozak primata.

With this large brain now affordable by cooking,

S ovim velikim mozgom koji je omogućilo kuhanje,

we went rapidly from raw foods to culture,

ubrzo smo prešli sa sirove hrane do kulture,

agriculture, civilization, grocery stores,

poljoprivrede, civilizacije, trgovina s hranom,

electricity, refrigerators,

struje, hladnjaka,

all of those things that nowadays

svih tih stvari koje nam danas

allow us to get all the energy we need

dopuštaju da dobijemo svu energiju koju trebamo

for the whole day in a single sitting

kako bi smo cijeli dan proveli samo sjedeći

at your favorite fast food joint.

u vašem najdražem fast food restoranu.

So what once was a solution

Ono što je jednom bilo riješenje

now became the problem,

sada je postalo problem,

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

i ironično, tražimo rješenje u sirovoj hrani.

So what is the human advantage?

Što je ljudska prednost?

What is it that we have

Što je to što imamo

that no other animal has?

a što druge životinje nemaju?

My answer is that we have the largest number

Moj odgovor je da imamo najveći broj

of neurons in the cerebral cortex,

neurona u moždanoj kori,

and I think that's the simplest explanation

i mislim da je to najjednostavnije objašnjenje

for our remarkable cognitive abilities.

za naše odlične kognitivne sposobnosti.

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

I što je to što mi radimo, a nijedna druga životinja ne radi,

and which I believe was fundamental

i što vjerujem je bila osnova

to allow us to reach that large,

koja nam je omogućila doseći taj veliki

largest number of neurons in the cortex?

najveći broj neurona u kori?

In two words, we cook.

U dvije riječi, mi kuhamo

No other animal cooks its food. Only humans do.

Nijedna druga životinja ne kuha svoju hranu. Samo ljudi da.

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

I mislim da smo tako postali ljudi.

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

Proučavanje ljudskog mozga je promjenilo način na koji razmišljam o hrani.

I now look at my kitchen,

Sada gledam svoju kuhinji,

and I bow to it,

i poklanjam joj se,

and I thank my ancestors for coming up

i zahvaljujem svojim precima što su došli

with the invention that probably made us humans.

do otkrića koje nas je vjerojatno učinilo ljudima.

Thank you very much.

Hvala vam puno.

(Applause)

(Pljesak)