What is so special about the human brain? Why is it that we study other animals instead of them studying us? What does a human brain have or do that no other brain does? When I became interested in these questions about 10 years ago, scientists thought they knew what different brains were made of. Though it was based on very little evidence, many scientists thought that all mammalian brains, including the human brain, were made in the same way, with a number of neurons that was always proportional to the size of the brain. This means that two brains of the same size, like these two, with a respectable 400 grams, should have similar numbers of neurons. Now, if neurons are the functional information processing units of the brain, then the owners of these two brains should have similar cognitive abilities. And yet, one is a chimp, and the other is a cow. Now maybe cows have a really rich internal mental life and are so smart that they choose not to let us realize it, but we eat them. I think most people will agree that chimps are capable of much more complex, elaborate and flexible behaviors than cows are. So this is a first indication that the "all brains are made the same way" scenario is not quite right.
Zašto je toliko poseban ljudski mozak? Zašto mi proučavamo druge životinje, umesto da one proučavaju nas? Šta to ljudski mozak ima ili radi što nijedan drugi mozak ne može? Kada sam počela da se zanimam za ova pitanja pre desetak godina, naučnici su mislili da znaju kakvog su sastava različiti mozgovi. Iako je, u osnovi, bilo malo dokaza mnogi naučnici su mislili da su mozgovi sisara, uključujući i ljudski mozak, potpuno isto načinjeni, sa brojem neurona koji je oduvek bio proporcionalan veličini mozga. To znači da dva mozga istih veličina, kao ova dva, od pristojnih 400 grama, treba da imaju isti broj neurona. Sada, ako su neuroni funkcionalne prenosne jedinice informacija, onda vlasnici ova dva mozga treba da imaju iste kognitivne sposobnosti. A ipak, jedan vlasnik je šimpanza, a drugi vlasnik je krava. Sada, možda krave imaju jako bogat unutrašnji, duševni život i toliko su pametne da su odlučile da nam ne dozvole da to shvatimo, ali mi njih jedemo. Mislim da bi se većina ljudi složila da su šimpanze sposobne za mnogo složenije, detaljnije i prilagodljivije ponašanje nego krave. Tako da je ovo prvi pokazatelj da scenario tipa: "Svi mozgovi su isto načinjeni", nije baš prihvatljiv.
But let's play along. If all brains were made the same way and you were to compare animals with brains of different sizes, larger brains should always have more neurons than smaller brains, and the larger the brain, the more cognitively able its owner should be. So the largest brain around should also be the most cognitively able. And here comes the bad news: Our brain, not the largest one around. It seems quite vexing. Our brain weighs between 1.2 and 1.5 kilos, but elephant brains weigh between four and five kilos, and whale brains can weigh up to nine kilos, which is why scientists used to resort to saying that our brain must be special to explain our cognitive abilities. It must be really extraordinary, an exception to the rule. Theirs may be bigger, but ours is better, and it could be better, for example, in that it seems larger than it should be, with a much larger cerebral cortex than we should have for the size of our bodies. So that would give us extra cortex to do more interesting things than just operating the body. That's because the size of the brain usually follows the size of the body. So the main reason for saying that our brain is larger than it should be actually comes from comparing ourselves to great apes. Gorillas can be two to three times larger than we are, so their brains should also be larger than ours, but instead it's the other way around. Our brain is three times larger than a gorilla brain.
Ali, hajde da i mi pretpostavimo isto. Ako su svi mozgovi načinjeni isto, i na vama je da poredite životinje sa različitom veličinom mozga, veći mozgovi bi uvek trebalo da imaju više neurona od manjih i što je mozak veći, veće bi trebale da budu i kognitivne sposobnosti njegovog vlasnika. Tako da najveći mozak treba da bude i najviše kognitivno sposoban. Ali, evo loših vesti. Naš mozak nije najveći u okruženju. Zvuči prilično uznemirujuće. Naš mozak je težine između 1,2 i 1,5 kilograma, ali mozak slona je težine od četiri do pet kilograma, a mozak kita može biti težine i do 9 kilograma, i zato su naučnici imali običaj da pribegavaju tvrdnji, da naši mozgovi mora da su posebni, jer to objašnjava naše kognitivne sposobnosti. Mora da je zaista izvanredan, izuzetak od pravila. Njihov je možda veći, ali naš je bolji, i može biti bolji, na primer, u tome, jer je veći nego što treba da bude, sa mnogo većim cerebralnim korteksom nego što bi trebalo, u odnosu na veličinu našeg tela. Tako da nam ostaje višak korteksa za neke interesantnije stvari od samog funkcionisanja tela. Veličina mozga obično je srazmerna veličini tela. Tako da glavni razlog što kažemo da je naš mozak veći nego što bi trebalo u stvari dolazi iz poređenja ljudi sa velikim majmunima. Gorile mogu biti dva ili tri puta veće nego što smo mi, tako da bi njihovi mozgovi trebalo isto tako da budu veći od naših, ali u stvari je obrnuto. Naš mozak je tri puta veći od mozga gorile.
The human brain also seems special in the amount of energy that it uses. Although it weighs only two percent of the body, it alone uses 25 percent of all the energy that your body requires to run per day. That's 500 calories out of a total of 2,000 calories, just to keep your brain working.
Ljudski mozak se isto tako čini poseban, i u količini energije koju koristi. Iako je težine samo dva procenta od ukupne težine tela, koristi 25 procenata ukupne energije koju vaše telo zahteva da bi funkcionisalo u jednom danu. To je 500 kalorija od ukupnih 2000 kalorija, samo da bi mozak bio u aktivnom stanju.
So the human brain is larger than it should be, it uses much more energy than it should, so it's special. And this is where the story started to bother me. In biology, we look for rules that apply to all animals and to life in general, so why should the rules of evolution apply to everybody else but not to us? Maybe the problem was with the basic assumption that all brains are made in the same way. Maybe two brains of a similar size can actually be made of very different numbers of neurons. Maybe a very large brain does not necessarily have more neurons than a more modest-sized brain. Maybe the human brain actually has the most neurons of any brain, regardless of its size, especially in the cerebral cortex. So this to me became the important question to answer: how many neurons does the human brain have, and how does that compare to other animals?
Znači, ljudski mozak je veći nego što bi trebalo da bude, koristi mnogo više energije nego što je potrebno - znači da je poseban. I evo gde je priča počela da mi smeta. U biologiji, mi tražimo pravila koja primenjujemo na životinje i život uopšte, i zašto se onda pravila evolucije primenjuju na sve ostale, ali ne i na nas? Možda je problem bio u osnovnoj pretpostavci da su svi mozgovi istog sastava. Možda, dva mozga istih veličina, u stvari, mogu biti sastavljeni od različitog broja neurona. Možda, veoma veliki mozak nema i veći broj neurona od manjeg mozga. Možda ljudski mozak u stvari ima najviše neurona od bilo kog mozga, nezavisno od veličine, posebno u cerebralnom korteksu. Tako da je ovo postalo za mene važno pitanje na koje treba da dam odgovor: koliko neurona ljudski mozak ima, i kako se to može porediti sa drugim životinjama?
Now, you may have heard or read somewhere that we have 100 billion neurons, so 10 years ago, I asked my colleagues if they knew where this number came from. But nobody did. I've been digging through the literature for the original reference for that number, and I could never find it. It seems that nobody had actually ever counted the number of neurons in the human brain, or in any other brain for that matter.
Možda ste čuli ili pročitali negde da mi imamo 100 milijardi neurona, i pre 10 godina, pitala sam svoje kolege da li možda znaju otkud ova brojka. Ali niko nije znao. Malo sam kopala po literaturi tražeći originalnu referencu za tu brojku, i nikada je nisam mogla pronaći. Izgleda da niko nije, u stvari, nikada izbrojao broj neurona u ljudskom mozgu, ili bilo kom drugom mozgu.
So I came up with my own way to count cells in the brain, and it essentially consists of dissolving that brain into soup. It works like this: You take a brain, or parts of that brain, and you dissolve it in detergent, which destroys the cell membranes but keeps the cell nuclei intact, so you end up with a suspension of free nuclei that looks like this, like a clear soup. This soup contains all the nuclei that once were a mouse brain. Now, the beauty of a soup is that because it is soup, you can agitate it and make those nuclei be distributed homogeneously in the liquid, so that now by looking under the microscope at just four or five samples of this homogeneous solution, you can count nuclei, and therefore tell how many cells that brain had. It's simple, it's straightforward, and it's really fast. So we've used that method to count neurons in dozens of different species so far, and it turns out that all brains are not made the same way. Take rodents and primates, for instance: In larger rodent brains, the average size of the neuron increases, so the brain inflates very rapidly and gains size much faster than it gains neurons. But primate brains gain neurons without the average neuron becoming any larger, which is a very economical way to add neurons to your brain. The result is that a primate brain will always have more neurons than a rodent brain of the same size, and the larger the brain, the larger this difference will be. Well, what about our brain then? We found that we have, on average, 86 billion neurons, 16 billion of which are in the cerebral cortex, and if you consider that the cerebral cortex is the seat of functions like awareness and logical and abstract reasoning, and that 16 billion is the most neurons that any cortex has, I think this is the simplest explanation for our remarkable cognitive abilities. But just as important is what the 86 billion neurons mean. Because we found that the relationship between the size of the brain and its number of neurons could be described mathematically, we could calculate what a human brain would look like if it was made like a rodent brain. So, a rodent brain with 86 billion neurons would weigh 36 kilos. That's not possible. A brain that huge would be crushed by its own weight, and this impossible brain would go in the body of 89 tons. I don't think it looks like us.
Tako da sam pronašla sopstveni način da izbrojim ćelije u mozgu, i u osnovi, sastoji se u rastvaranju mozga u supu. To ovako funkcioniše: mozak, ili delove mozga, rastvorite u deterdžentu, koji uništava ćelijske membrane ali ćelijska jezgra ostaju netaknuta, i na kraju završite sa suspenzijom slobodnih jezgara koja izgleda ovako, kao bistra supa. Ova supa sadrži sva jezgra koja su nekada bila u mozgu miša. Sada, prednosti supe su te da je možete promućkati i naterati jezgra da se pravilno rasporede u tečnosti, tako da posmatranjem pod mikroskopom samo četiri ili pet uzoraka ovog homogenog rastvora možete da izbrojite jezgra, a potom i kažete od koliko ćelija se mozak sastojao. Jednostavno je i direktno, i veoma brzo. Tako da smo mi koristili tu metodu da izbrojimo neurone različitih vrsta, i ispostavlja se da nisu svi mozgovi istog sastava. Uzmite glodare i primate, na primer. U većim mozgovima glodara, prosečna veličina neurona raste, tako da se mozak uvećava veoma brzo i uvećava se mnogo brže nego što postiže veći broj neurona. Ali kod primata, mozak postiže veći broj neurona bez uvećavanja samog neurona, što je prilično ekonomičan način dodavanja neurona vašem mozgu. Kao rezultat, mozak primata će uvek imati više neurona od mozga glodara koji je iste veličine, i što je mozak veći, veća će biti i razlika. A, šta je onda sa našim mozgovima? Otkrili smo da mi u proseku imamo 86 milijardi neurona, 16 milijardi su u cerebralnom korteksu, i ako uzmete u obzir da je cerebralni korteks glavni za funkcije, kao što su: svesnost, logično i apstraktno rezonovanje, i da je 16 milijardi najveći broj neurona koji bilo koji korteks sadrži, mislim da je ovo najjednostavnije objašnjenje naših izvanrednih kognitivnih sposobnosti. Ali isto tako važno je, šta znači uopšte broj od 86 milijardi neurona. Zato što smo pronašli da veza između veličine mozga i broja neurona može biti matematički opisana, možemo pokazati kako bi ljudski mozak izgledao da je po sastavu kao mozak glodara. Tako da bi mozak glodara sa 86 milijardi neurona bio težine 36 kilograma. To nije moguće. Toliki mozak bi bio uništen svojom težinom, i takav mozak bi išao uz telo težine od 89 tona. Mislim da to ne liči na nas.
So this brings us to a very important conclusion already, which is that we are not rodents. The human brain is not a large rat brain. Compared to a rat, we might seem special, yes, but that's not a fair comparison to make, given that we know that we are not rodents. We are primates, so the correct comparison is to other primates. And there, if you do the math, you find that a generic primate with 86 billion neurons would have a brain of about 1.2 kilos, which seems just right, in a body of some 66 kilos, which in my case is exactly right, which brings us to a very unsurprising but still incredibly important conclusion: I am a primate. And all of you are primates.
Tako da nas ovo već dovodi do važnog zaključka, koje glasi: mi nismo glodari. Mozak ljudi nije veliki mozak pacova. U poređenju sa pacovima, mi možda izgledamo posebno, ali to nije pravedno poređenje znajući da mi nismo glodari. Mi smo primati, tako da je pravilno poređenje ono sa drugim primatima. I tu, ako odradite matematiku, pronalazite da će primat sa 86 milijardi neurona imati mozak težine oko 1,2 kilograma, što je i sasvim dovoljno, za nekoga ko je težine od nekih 66 kilograma, što je u mom slučaju potpuno tačno, i to nas dovodi do veoma poznatog, ali ipak neverovatno značajnog zaključka: Ja sam primat. I svi vi ste primati.
And so was Darwin. I love to think that Darwin would have really appreciated this. His brain, like ours, was made in the image of other primate brains.
Kao što je i Darvin bio. Volim da mislim da bi Darvin zaista cenio ovo. Njegov mozak, kao i naš napravljen je po ugledu na druge primate.
So the human brain may be remarkable, yes, but it is not special in its number of neurons. It is just a large primate brain. I think that's a very humbling and sobering thought that should remind us of our place in nature.
Tako da ljudski mozak možda jeste izvanredan, da, ali nije poseban u pogledu broja neurona. Samo je to jedan veliki mozak primata. Mislim da je to jedna veoma skromna i trezvena misao, koja treba da nas podseti koje je naše mesto u prirodi.
Why does it cost so much energy, then? Well, other people have figured out how much energy the human brain and that of other species costs, and now that we knew how many neurons each brain was made of, we could do the math. And it turns out that both human and other brains cost about the same, an average of six calories per billion neurons per day. So the total energetic cost of a brain is a simple, linear function of its number of neurons, and it turns out that the human brain costs just as much energy as you would expect. So the reason why the human brain costs so much energy is simply because it has a huge number of neurons, and because we are primates with many more neurons for a given body size than any other animal, the relative cost of our brain is large, but just because we're primates, not because we're special.
Zašto je onda potrebno utrošiti toliko energije? Neki ljudi su pronašli koliko je energije potrebno ljudskom mozgu i mozgu nekih drugih vrsta, i sada kada znamo koliko neurona svaki mozak ima, možemo primeniti matematiku. Ispostavlja se da je i za ljudske i za mozgove drugih vrsta, utrošak isti, prosečno šest kalorija na milijardu neurona, dnevno. Tako da je ukupni, energetski utrošak jednostavna, linearna funkcija broja neurona, i ispostavilo se da ljudski mozak troši onoliko energije koliko se i očekivalo. Tako da je razlog zbog kojeg ljudski mozak troši toliko energije, jednostavan, jer ima veliki broj neurona, i zato što smo mi primati sa mngo većim brojem neurona u odnosu na veličinu tela od bilo koje druge vrste, relativna potrošnja našeg mozga je ogromna ali samo zato jer smo mi primati, ne zato što smo posebni.
Last question, then: how did we come by this remarkable number of neurons, and in particular, if great apes are larger than we are, why don't they have a larger brain than we do, with more neurons? When we realized how much expensive it is to have a lot of neurons in the brain, I figured, maybe there's a simple reason. They just can't afford the energy for both a large body and a large number of neurons. So we did the math. We calculated on the one hand how much energy a primate gets per day from eating raw foods, and on the other hand, how much energy a body of a certain size costs and how much energy a brain of a certain number of neurons costs, and we looked for the combinations of body size and number of brain neurons that a primate could afford if it ate a certain number of hours per day.
Poslednje pitanje, onda: kako smo se mi zadesili sa ovako velikim brojem neurona, iako su veliki majmuni veći od nas, zašto oni nemaju veći mozak, sa više neurona? Kada smo shvatili koliko je zahtevno imati puno neurona u mozgu, možda je razlog jednostavan. Oni ne mogu da priušte dovoljno energije i za ogromna tela i za veliki broj neurona. Tako da smo odradili matematiku. Izračunali smo, sa jedne strane, koliko je energije potrebno sisaru dnevno, ako se hrane sirovom hranom, i sa druge strane, koliko energije za telo određene veličine. i koliko je energije potrebno mozgu koji ima određeni broj neurona, i tragali smo za kombinacijom veličine tela i broja neurona koje primat sebi može priuštiti ako jede određen broj sati dnevno.
And what we found is that because neurons are so expensive, there is a tradeoff between body size and number of neurons. So a primate that eats eight hours per day can afford at most 53 billion neurons, but then its body cannot be any bigger than 25 kilos. To weigh any more than that, it has to give up neurons. So it's either a large body or a large number of neurons. When you eat like a primate, you can't afford both.
I ono što smo pronašli je to da su neuroni veoma skupi. Postoji kompromis između veličine tela i broja neurona. Tako da primat koji jede osam sati dnevno može najviše priuštiti 53 milijarde neurona, ali onda telo ne može postati teže od 25 kilograma. Veća težina znači i manji broj neurona. Tako da ili je telo veće ili je veći broj neurona. Kada se hranite kao primati, ne možete sebi priuštiti i jedno i drugo.
One way out of this metabolic limitation would be to spend even more hours per day eating, but that gets dangerous, and past a certain point, it's just not possible. Gorillas and orangutans, for instance, afford about 30 billion neurons by spending eight and a half hours per day eating, and that seems to be about as much as they can do. Nine hours of feeding per day seems to be the practical limit for a primate.
Jedini izlaz iz ovakvih postavljenih metaboličkih granica bi bio: još više sati utrošiti na ishranu, ali to već postaje opasno, i posle određene granice, nije ni moguće. Gorile i orangutani, na primer, mogu priuštiti sebi 30 milijardi neurona, provodeći dnevno 8 i po sati u jelu, i to je izgleda i najviše što mogu. Devet sati hranjenja dnevno, izgleda da je realna granica, koja je postavljena za primate.
What about us? With our 86 billion neurons and 60 to 70 kilos of body mass, we should have to spend over nine hours per day every single day feeding, which is just not feasible. If we ate like a primate, we should not be here.
Šta je sa nama? Sa naših 86 milijardi neurona i od 60 do 70 kilograma telesne mase, trebalo bi da provodimo preko devet sati svakog dana, hraneći se, što prosto, nije izvodljivo. Da jedemo kao primati, ne bi trebalo da budemo ovde.
How did we get here, then? Well, if our brain costs just as much energy as it should, and if we can't spend every waking hour of the day feeding, then the only alternative, really, is to somehow get more energy out of the same foods. And remarkably, that matches exactly what our ancestors are believed to have invented one and a half million years ago, when they invented cooking. To cook is to use fire to pre-digest foods outside of your body. Cooked foods are softer, so they're easier to chew and to turn completely into mush in your mouth, so that allows them to be completely digested and absorbed in your gut, which makes them yield much more energy in much less time. So cooking frees time for us to do much more interesting things with our day and with our neurons than just thinking about food, looking for food, and gobbling down food all day long.
Kako smo u stvari dospeli ovde, onda? Pa, ako našim mozgovima treba energije koliko je potrebno, i ako ne možemo da provedemo svaki sat tokom dana, hraneći se onda je jedina mogućnost, zaista da nekako dobijemo više energije iz iste hrane. I izvanredno, to se poklapa upravo sa otkrićem naših predaka pre milion i po godina, kada su i izumeli kuvanje. Kuvanje znači koristiti vatru da bi se hrana mogla bolje svariti. Kuvana hrana je mekša, tako da je lakša da se žvaće i potpuno se pretvara u kašu u ustima, tako da može biti potpuno svarena i apsorbovana u stomaku, što za kraće vreme donosi mnogo više energije u mnogo kraćem vremenu. Tako da kuvanje nama štedi vreme da bismo radili neke mnogo interesantnije stvari u našem danu i sa našim neuronima, da ne bismo samo razmišljali o hrani, tragali za hranom i gutali hranu po čitav dan.
So because of cooking, what once was a major liability, this large, dangerously expensive brain with a lot of neurons, could now become a major asset, now that we could both afford the energy for a lot of neurons and the time to do interesting things with them. So I think this explains why the human brain grew to become so large so fast in evolution, all of the while remaining just a primate brain. With this large brain now affordable by cooking, we went rapidly from raw foods to culture, agriculture, civilization, grocery stores, electricity, refrigerators, all of those things that nowadays allow us to get all the energy we need for the whole day in a single sitting at your favorite fast food joint. So what once was a solution now became the problem, and ironically, we look for the solution in raw food.
I tako, zbog kuvanja, ono što je nekada bila velika odgovornost, ovako veliki veoma skup mozak sa puno neurona, sada može postati naše glavno oruđe, sad kada možemo priuštiti i energiju za puno neurona i vreme, da bismo uradili zanimljive stvari sa njima. Tako da ja mislim ovo objašnjava zašto je ljudski mozak tako brzo postao razvijen tokom evolucije, a sve vreme ostajući samo mozak primata. Sa ovako velikim mozgom, kojeg možemo i koristiti, zahvaljujući kuvanju, munjevito smo prešli sa sirove hrane na kulture, poljoprivredu, civilizaciju, bakalnice, elektricitet, frižidere, sve te stvari koje nam danas omogućavaju da priuštimo svu potrebnu energiju za ceo dan, samo u jednom obroku u omiljenom lancu brze hrane. Tako da, ono što je nekada bilo rešenje, sada postaje problem, i ironično, to rešenje tražimo u sirovoj hrani.
So what is the human advantage? What is it that we have that no other animal has? My answer is that we have the largest number of neurons in the cerebral cortex, and I think that's the simplest explanation for our remarkable cognitive abilities. And what is it that we do that no other animal does, and which I believe was fundamental to allow us to reach that large, largest number of neurons in the cortex? In two words, we cook. No other animal cooks its food. Only humans do. And I think that's how we got to become human.
I šta je prednost ljudi? Šta je to što mi imamo, a nijedna druga životinja nema? Moj odgovor je da imamo najveći broj neurona u cerebralnom korteksu, i mislim da je to najjednostavnije objašnjenje za naše izuzetne kognitivne sposobnosti. A šta je ono što mi radimo, a nijedna druga životinja ne radi i što mislim da je bilo fundamentalno da bismo uopšte mogli da dosegnemo taj veliki, najveći broj neurona u moždanoj kori? Dve reči: mi kuvamo. Nijedna druga životinja ne kuva svoju hranu. Samo ljudi to rade. I ja mislim da smo upravo tako mi i postali ljudi.
Studying the human brain changed the way I think about food. I now look at my kitchen, and I bow to it, and I thank my ancestors for coming up with the invention that probably made us humans. Thank you very much. (Applause)
Proučavanje ljudskog mozga je promenilo način na koji razmišljam o hrani. Sada pogledam u svoju kuhinju i klanjam se, i zahvaljujem našim precima što su nabasali na otkriće koje nas je verovatno i načinilo ljudima. Hvala vam mnogo. (Aplauz)