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: Que ten de especial o cerebro humano?

Filmed:
3,044,795 views

O cerebro humano é desconcertante. É estrañamente grande tendo en conta o tamaño do noso corpo, emprega unha cantidade tremenda de enerxía para o seu peso e ten un córtex cerebral singularmente denso. Pero, por que? A neurocientífica Suzana Herculano-Houzel pon a súa gorra de detective e guíanos neste misterio. Ao facer "sopa de cerebro" chega a unha conclusión sorprendente.
- 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.

00:12
What is so special about the human brain?
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Que ten de especial o cerebro humano?
00:15
Why is it that we study other animals
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Por que estudamos os outros animais
00:17
instead of them studying us?
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mais eles non nos estudan a nós?
00:19
What does a human brain have or do
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Que ten ou fai o cerebro humano
00:21
that no other brain does?
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que non fai nin ten ningún outro?
Cando comecei a interesarme
nestas cuestións hai uns 10 anos,
00:23
When I became interested
in these questions about 10 years ago,
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00:26
scientists thought they knew
what different brains were made of.
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os científicos crían saber
de que estaban feitos os cerebros.
00:28
Though it was based on very little evidence,
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Malia basearse en pequenas evidencias,
00:30
many scientists thought that all mammalian brains,
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moitos científicos crían que todos os
cerebros de mamíferos,
00:32
including the human brain,
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incluíndo o cerebro humano,
00:34
were made in the same way,
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estaban feitos igual,
00:35
with a number of neurons that was always
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cun número de neuronas que era
00:37
proportional to the size of the brain.
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sempre proporcional ao tamaño do cerebro.
00:39
This means that two brains of the same size,
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Isto significa que dous cerebros
do mesmo tamaño,
00:41
like these two, with a respectable 400 grams,
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como estes dous, cos seus 400 gramos,
00:45
should have similar numbers of neurons.
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deberían ter un número
semellante de neuronas.
00:47
Now, if neurons are the functional
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Pero se as neuronas
son as unidades funcionais
00:49
information processing units of the brain,
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de procesamento de información do cerebro,
00:52
then the owners of these two brains
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os donos deses dous cerebros
00:54
should have similar cognitive abilities.
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deberían ter habilidades
cognitivas semellantes.
00:56
And yet, one is a chimp,
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E porén, un é un chimpancé,
00:59
and the other is a cow.
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e o outro é unha vaca.
01:01
Now maybe cows have a really rich
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Ben, é posible que as vacas teñan
unha vizosa vida interior
01:04
internal mental life and are so smart
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e sexan tan intelixentes
01:06
that they choose not to let us realize it,
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que prefiren que non nos deamos de conta,
01:10
but we eat them.
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pero comémolas.
01:11
I think most people will agree
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Penso que a maioría estará de acordo
01:13
that chimps are capable of much more complex,
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en que os chimpancés poden ter
un comportamento moito máis complexo,
elaborado e flexible ca unha vaca.
01:15
elaborate and flexible behaviors than cows are.
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01:18
So this is a first indication that the
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Este é un primeiro indicio de que
01:20
"all brains are made the same way" scenario
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"todos os cerebros están
feitos da mesma maneira"
01:22
is not quite right.
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non é exactamente así.
01:24
But let's play along.
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Pero sigamos.
Se todos os cerebros estivesen
feitos da mesma maneira
01:25
If all brains were made the same way
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01:27
and you were to compare animals
with brains of different sizes,
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e comparásemos animais
con cerebros de tamaños diferentes,
01:30
larger brains should always have more neurons
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os máis grandes deberían ter máis neuronas
01:32
than smaller brains,
and the larger the brain,
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cós máis pequenos,
e canto maior for o cerebro,
01:34
the more cognitively able its owner should be.
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máis habilidades cognitivas
debería ter o dono.
01:37
So the largest brain around should also be
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Así que o cerebro máis grande
debería ser tamén
01:39
the most cognitively able.
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o de maior capacidade cognitiva.
01:42
And here comes the bad news:
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E aquí veñen as malas noticias:
01:43
Our brain, not the largest one around.
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O noso cerebro non é o máis grande.
01:46
It seems quite vexing.
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Resulta un pouco desacougante.
01:47
Our brain weighs between 1.2 and 1.5 kilos,
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O noso cerebro pesa entre 1,2 e 1,5 kg,
01:50
but elephant brains weigh between four and five kilos,
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pero o cerebro dun elefante
pesa entre 4 e 5 kg
01:54
and whale brains can weigh up to nine kilos,
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e o das baleas pode pesar ata 9 kg,
01:56
which is why scientists used to resort to saying
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é por isto que os científicos, para
explicar as nosas habilidades cognitivas,
02:01
that our brain must be special
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acababan por dicir
que o noso cerebro tiña que ser especial.
02:03
to explain our cognitive abilities.
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02:06
It must be really extraordinary,
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Tiña que ser extraordinario de verdade,
02:09
an exception to the rule.
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unha excepción á regra.
02:11
Theirs may be bigger, but ours is better,
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O deles pode ser maior
pero o noso é mellor,
02:14
and it could be better, for example,
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e podería ser mellor, por exemplo,
02:16
in that it seems larger than it should be,
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porque parece maior do que debería ser,
02:18
with a much larger cerebral cortex
than we should have
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cun córtex cerebral moito maior
do que deberiamos ter
02:21
for the size of our bodies.
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para o tamaño dos nosos corpos.
02:22
So that would give us extra cortex
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Iso daríanos córtex extra
02:24
to do more interesting things
than just operating the body.
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para facer cousas máis interesantes
amais de manexar o corpo.
02:27
That's because the size of the brain
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Iso é porque o tamaño do cerebro
02:29
usually follows the size of the body.
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normalmente está relacionado
co tamaño do corpo.
02:31
So the main reason for saying that
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Así que a principal razón para dicir que
02:33
our brain is larger than it should be
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o noso cerebro é maior
do que debería ser
02:35
actually comes from comparing ourselves
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vén en realidade de comparármonos
02:37
to great apes.
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cos grandes simios.
Os gorilas poden ser de dúas a tres veces
meirandes ca nós,
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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así que os seus cerebros deberían ser
tamén meirandes cós nosos,
02:44
but instead it's the other way around.
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pero é ao revés.
O noso cerebro é tres veces máis grande
có cerebro dun gorila.
02:46
Our brain is three times larger than a gorilla brain.
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02:49
The human brain also seems special
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O cerebro humano tamén semella especial
02:51
in the amount of energy that it uses.
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na cantidade de enerxía que usa.
02:53
Although it weighs only two percent of the body,
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Aínda que só pesa o 2 % do corpo,
02:56
it alone uses 25 percent of all the energy
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usa o 25 % de toda a enerxía
02:59
that your body requires to run per day.
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que o corpo require
para funcionar cada día.
03:02
That's 500 calories out of a total of 2,000 calories,
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Iso son 500 calorías
dun total de 2000 calorías,
03:05
just to keep your brain working.
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só para manter o cerebro funcionando.
03:07
So the human brain is larger than it should be,
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Entón, o cerebro humano é
máis grande do que debería,
03:10
it uses much more energy than it should,
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usa moita máis enerxía do que debería
03:12
so it's special.
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e, polo tanto, é especial.
03:14
And this is where the story started to bother me.
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E aquí é onde a historia
empezou a intrigarme.
03:16
In biology, we look for rules
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En bioloxía buscamos regras
03:18
that apply to all animals and to life in general,
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que se apliquen a todos os
animais e á vida en xeral.
03:21
so why should the rules of evolution
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Por que as regras da evolución
03:23
apply to everybody else but not to us?
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se ían aplicar a todo o mundo
menos a nós?
Quizais o problema era a asunción básica
03:26
Maybe the problem was with the basic assumption
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de todos os cerebros estaren feitos igual.
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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Quizais dous cerebros de tamaño similar
03:32
can actually be made of
very different numbers of neurons.
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poden ter un número
moi diferente de neuronas.
03:35
Maybe a very large brain
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Quizais un cerebro moi grande
03:36
does not necessarily have more neurons
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non ten por que ter máis neuronas
03:38
than a more modest-sized brain.
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ca un cerebro de tamaño máis modesto.
03:40
Maybe the human brain
actually has the most neurons
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Quizais o cerebro humano ten
máis neuronas ca calquera outro cerebro
03:43
of any brain, regardless of its size,
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a pesar do seu tamaño,
03:46
especially in the cerebral cortex.
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especialmente no córtex cerebral.
03:48
So this to me became
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Así que para min, isto converteuse
03:50
the important question to answer:
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na pregunta que había que resolver:
03:51
how many neurons does the human brain have,
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Cantas neuronas ten o cerebro humano,
03:54
and how does that compare to other animals?
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e como se compara co doutros animais?
03:56
Now, you may have heard or read somewhere
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Ben, seguramente escoitastes ou lestes
03:59
that we have 100 billion neurons,
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que temos 100 mil millóns de neuronas,
así que hai 10 anos, pregunteilles
aos meus colegas
04:01
so 10 years ago, I asked my colleagues
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04:03
if they knew where this number came from.
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se sabían de onde saíra este número.
04:05
But nobody did.
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Pero ninguén o sabía.
04:06
I've been digging through the literature
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Estiven investigando na literatura
04:08
for the original reference for that number,
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a referencia orixinal deste número,
04:10
and I could never find it.
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e nunca cheguei a atopala.
04:11
It seems that nobody had actually ever counted
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Semella que ninguén chegou a contar
04:14
the number of neurons in the human brain,
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o número de neuronas do cerebro humano
04:16
or in any other brain for that matter.
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ou de ningún outro, para o caso.
04:18
So I came up with my own way
to count cells in the brain,
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Así que inventei o meu propio xeito
de contar células no cerebro
04:22
and it essentially consists of
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e esencialmente consiste en
04:24
dissolving that brain into soup.
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disolver ese cerebro en sopa.
04:27
It works like this:
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Funciona así:
04:29
You take a brain, or parts of that brain,
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Cóllese un cerebro, ou partes del,
04:32
and you dissolve it in detergent,
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e disólvese en deterxente,
04:34
which destroys the cell membranes
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que destrúe as membranas das células
04:35
but keeps the cell nuclei intact,
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pero mantén o núcleo celular intacto,
04:38
so you end up with a suspension of free nuclei
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e o resultado é unha suspensión
de núcleos soltos
04:41
that looks like this,
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que se parece a isto,
04:43
like a clear soup.
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unha sopa clara.
04:44
This soup contains all the nuclei
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Esta sopa contén todos os núcleos
04:46
that once were a mouse brain.
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que un día compuxeron o cerebro dun rato.
04:48
Now, the beauty of a soup is that because it is soup,
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Agora ben, a beleza dunha sopa
é que ao ser sopa
04:51
you can agitate it and make those nuclei
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pódese abanear e facer que eses núcleos
04:54
be distributed homogeneously in the liquid,
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se distribúan no líquido homoxeneamente,
04:56
so that now by looking under the microscope
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así que agora ao mirar
debaixo do microscopio
04:58
at just four or five samples
of this homogeneous solution,
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catro ou cinco mostras
desta solución homoxénea
05:02
you can count nuclei, and therefore tell
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pódense contar núcleos e dese xeito dicir
05:05
how many cells that brain had.
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cantas células tiña ese cerebro.
05:06
It's simple, it's straightforward,
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É simple, é sinxelo,
05:08
and it's really fast.
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e é moi rápido.
05:09
So we've used that method to count neurons
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Así que usamos ese método
para contar neuronas
05:11
in dozens of different species so far,
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en ducias de especies diferentes
05:14
and it turns out that all brains
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e resulta que os cerebros
05:15
are not made the same way.
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non están todos feitos do mesmo xeito.
05:18
Take rodents and primates, for instance:
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Collamos os roedores e
os primates, por exemplo.
05:20
In larger rodent brains, the average size
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Nos cerebros de roedores grandes,
o tamaño medio
05:22
of the neuron increases,
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das neuronas increméntase,
05:24
so the brain inflates very rapidly
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así que o cerebro medra rapidamente
05:27
and gains size much faster than it gains neurons.
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e gaña tamaño moito máis rápido
do que gaña neuronas.
05:30
But primate brains gain neurons
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Pero os cerebros dos primates
gañan neuronas
05:32
without the average neuron becoming any larger,
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sen que o tamaño medio destas aumente,
05:34
which is a very economical way
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o que é un xeito moi económico
05:35
to add neurons to your brain.
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de engadir neuronas ao cerebro.
05:37
The result is that a primate brain
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O resultado é que o cerebro dun primate
05:39
will always have more neurons than
a rodent brain of the same size,
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sempre terá máis neuronas có
cerebro dun roedor do mesmo tamaño,
05:42
and the larger the brain,
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e canto maior for o cerebro,
05:44
the larger this difference will be.
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maior será esta diferenza.
05:46
Well, what about our brain then?
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Ben, entón que pasa co noso cerebro?
05:48
We found that we have, on average,
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Resulta que temos, de media,
05:50
86 billion neurons,
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86 mil millóns de neuronas,
05:51
16 billion of which are in the cerebral cortex,
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e destas, 16 mil millóns están
no córtex cerebral.
05:54
and if you consider that the cerebral cortex
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Se se considera que o córtex cerebral
05:56
is the seat of functions like
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é a sede de funcións como a consciencia
06:00
awareness and logical and abstract reasoning,
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e o razoamento lóxico e abstracto,
06:03
and that 16 billion is the most neurons
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e que 16 mil millóns é
o máximo de neuronas
06:06
that any cortex has,
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que ten un córtex,
penso que esta é a explicación máis simple
06:08
I think this is the simplest explanation
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06:10
for our remarkable cognitive abilities.
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para as nosas extraordinarias
habilidades cognitivas.
Pero tan importante é o que significan
os 86 mil millóns de neuronas.
06:13
But just as important is what
the 86 billion neurons mean.
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06:16
Because we found that the relationship
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Porque descubrimos que a relación
06:18
between the size of the brain
and its number of neurons
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entre o tamaño do cerebro e
o número de neuronas
06:20
could be described mathematically,
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poderíase describir matematicamente,
06:22
we could calculate what a human brain
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poderiamos calcular como
sería un cerebro humano
06:24
would look like if it was made like a rodent brain.
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se fose como o cerebro dun roedor.
06:27
So, a rodent brain with 86 billion neurons
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Así que o cerebro dun roedor
con 86 mil millóns de neuronas
06:30
would weigh 36 kilos.
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pesaría 36 kg.
06:33
That's not possible.
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Isto non é posible.
06:35
A brain that huge would be crushed
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Un cerebro tan enorme
acabaría esmagado
06:37
by its own weight,
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polo seu propio peso.
06:38
and this impossible brain would go
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E a este cerebro imposible
corresponderíalle
06:40
in the body of 89 tons.
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un corpo de 89 toneladas.
06:44
I don't think it looks like us.
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Non creo que se pareza a nós.
06:46
So this brings us to a very important
conclusion already,
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Así que isto xa nos leva a unha
conclusión moi importante:
06:48
which is that we are not rodents.
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nós non somos roedores.
06:51
The human brain is not a large rat brain.
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O cerebro humano non é
o cerebro dunha rata grande.
06:54
Compared to a rat, we might seem special, yes,
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Comparados cunha rata, poderiamos
parecer especiais, si,
06:57
but that's not a fair comparison to make,
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pero non é unha comparación moi xusta,
06:59
given that we know that we are not rodents.
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dado que sabemos que non somos roedores.
07:01
We are primates,
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Somos primates,
07:02
so the correct comparison is to other primates.
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así que a comparación correcta
é con outros primates.
07:05
And there, if you do the math,
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E aí, se se fan a contas,
07:06
you find that a generic primate
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resulta que un primate normal
07:09
with 86 billion neurons
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con 86 mil millóns de neuronas
07:11
would have a brain of about 1.2 kilos,
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tería un cerebro de case 1,2 kg
07:14
which seems just right,
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que encaixa perfectamente
07:16
in a body of some 66 kilos,
185
424561
1972
nun corpo duns 66 quilos,
07:18
which in my case is exactly right,
186
426533
2645
que no meu caso é exactamente ese.
07:21
which brings us to a very unsurprising
187
429178
2620
Isto lévanos a unha conclusión
que non sorprende moito
07:23
but still incredibly important conclusion:
188
431798
2969
pero que é moi importante:
07:26
I am a primate.
189
434767
1341
Son un primate.
07:28
And all of you are primates.
190
436108
2698
E todos vós sodes primates.
07:30
And so was Darwin.
191
438806
1900
E Darwin tamén o era.
07:32
I love to think that Darwin
would have really appreciated this.
192
440706
2940
Encántame pensar que Darwin
apreciaría moito isto.
07:35
His brain, like ours,
193
443646
1967
O seu cerebro, coma o noso,
07:37
was made in the image of other primate brains.
194
445613
3511
estaba feito á imaxe do
cerebro doutros primates.
07:41
So the human brain may be remarkable, yes,
195
449124
2302
Así que o cerebro humano
pode ser extraordinario, si,
07:43
but it is not special in its number of neurons.
196
451426
2781
pero non é especial no
número de neuronas que ten.
07:46
It is just a large primate brain.
197
454207
1855
É só un cerebro de primate grande.
07:48
I think that's a very humbling and sobering thought
198
456062
3044
Penso que ese é un pensamento
moi humilde e realista
07:51
that should remind us of our place in nature.
199
459106
3063
que nos debería lembrar
o noso lugar na natureza.
07:54
Why does it cost so much energy, then?
200
462169
2644
Por que precisa tanta enerxía, entón?
07:56
Well, other people have figured out
201
464813
1447
Ben, outros descubriron
07:58
how much energy the human brain
202
466260
1503
canta enerxía gasta
o cerebro humano e
o doutras especies,
07:59
and that of other species costs,
203
467763
1407
08:01
and now that we knew how many neurons
204
469170
1652
e agora que sabemos
cantas neuronas
08:02
each brain was made of, we could do the math.
205
470822
2342
ten cada cerebro, podemos
sacar conclusións.
08:05
And it turns out that both human
206
473164
1866
E resulta que tanto o cerebro humano
08:07
and other brains cost about the same,
207
475030
2823
coma outros cerebros gastan o mesmo,
08:09
an average of six calories
per billion neurons per day.
208
477853
3421
unha media de seis calorías por
cada mil millóns de neuronas por día.
08:13
So the total energetic cost of a brain
209
481274
2139
Así que o custo total
de enerxía dun cerebro
08:15
is a simple, linear function
210
483413
2034
é unha función simple, lineal,
08:17
of its number of neurons,
211
485447
1709
do seu número de neuronas,
08:19
and it turns out that the human brain
212
487156
2183
e resulta que o cerebro humano
08:21
costs just as much energy as you would expect.
213
489339
3841
gasta tanta enerxía
como poderiamos agardar.
08:25
So the reason why the human brain
214
493180
2091
Así que a razón pola que
o cerebro humano
08:27
costs so much energy is simply because
215
495271
1672
gasta tanta enerxía é
simplemente porque
08:28
it has a huge number of neurons,
216
496943
1983
ten un número enorme de neuronas,
08:30
and because we are primates
217
498926
1485
e porque somos primates
08:32
with many more neurons for a given body size
218
500411
2499
con moitas máis neuronas para
unha masa corporal determinada
08:34
than any other animal,
219
502910
1522
ca calquera outro animal.
08:36
the relative cost of our brain is large,
220
504432
3540
O custo relativo do noso cerebro é grande
08:39
but just because we're primates,
not because we're special.
221
507972
3001
pero só porque somos primates,
non por sermos especiais.
08:42
Last question, then:
222
510973
1190
Unha última cuestión, entón:
08:44
how did we come by this
remarkable number of neurons,
223
512163
3115
como chegamos a este
extraordinario número de neuronas?
08:47
and in particular, if great apes
224
515278
1900
E, en particular, se os grandes primates
08:49
are larger than we are,
225
517178
1555
son máis grandes ca nós,
08:50
why don't they have a larger brain
than we do, with more neurons?
226
518733
3765
por que non teñen un cerebro máis grande
có noso con máis neuronas?
08:54
When we realized how much expensive it is
227
522498
2090
Cando nos demos de conta do que custa
08:56
to have a lot of neurons in the brain, I figured,
228
524588
2333
ter tantas neuronas no cerebro,
pensei: talvez hai unha razón simple.
08:58
maybe there's a simple reason.
229
526921
2003
09:00
They just can't afford the energy
230
528924
1683
Eles non poden permitirse a enerxía
09:02
for both a large body
and a large number of neurons.
231
530607
2950
para un corpo grande e
un gran número de neuronas.
09:05
So we did the math.
232
533557
1429
Así que fixemos contas.
09:06
We calculated on the one hand
233
534986
1600
Por unha parte, calculamos
09:08
how much energy a primate gets per day
234
536586
1941
canta enerxía consegue ao día un primate
09:10
from eating raw foods,
235
538527
1350
comendo alimentos crus
09:11
and on the other hand, how much energy
236
539877
2037
e, por outra parte, canta enerxía
09:13
a body of a certain size costs
237
541914
1764
precisa un corpo dun determinado tamaño
09:15
and how much energy a brain of a
certain number of neurons costs,
238
543678
3387
e canta enerxía precisa un cerebro
dun determinado número de neuronas,
09:19
and we looked for the combinations
239
547065
1489
e buscamos as combinacións
09:20
of body size and number of brain neurons
240
548554
2411
de tamaño de corpo e número de neuronas
que un primate podería permitirse
09:22
that a primate could afford
241
550965
1270
09:24
if it ate a certain number of hours per day.
242
552235
2548
se comese durante certo
número de horas por día.
09:26
And what we found is that
243
554783
1816
E descubrimos que,
como as neuronas precisan tanta enerxía,
09:28
because neurons are so expensive,
244
556599
1712
09:30
there is a tradeoff between
body size and number of neurons.
245
558311
3370
hai unha compensación entre
o tamaño do corpo e o número de neuronas.
09:33
So a primate that eats eight hours per day
246
561681
2951
Así que un primate que
come oito horas cada día
09:36
can afford at most 53 billion neurons,
247
564632
3024
pode ter como moito
53 mil millóns de neuronas
09:39
but then its body cannot be any bigger
248
567656
1727
pero entón o seu corpo non pode
09:41
than 25 kilos.
249
569383
1954
superar os 25 kg.
09:43
To weigh any more than that,
250
571337
1701
Para pesar algo máis,
09:45
it has to give up neurons.
251
573038
1769
ten que renunciar a neuronas.
09:46
So it's either a large body
252
574807
2653
Así que ou se ten un corpo grande
09:49
or a large number of neurons.
253
577460
1495
ou un número alto de neuronas.
09:50
When you eat like a primate,
254
578955
1365
Se comes coma un primate
09:52
you can't afford both.
255
580320
2236
non podes ter as dúas cousas.
09:54
One way out of this metabolic limitation
256
582556
1964
Unha forma de superar
esta limitación metabólica
09:56
would be to spend even more hours per day eating,
257
584520
3401
sería pasar aínda máis
horas comendo cada día.
09:59
but that gets dangerous,
258
587921
1363
pero iso é perigoso
10:01
and past a certain point, it's just not possible.
259
589284
2719
e, pasado certo punto, non é posible.
10:04
Gorillas and orangutans, for instance,
260
592003
1537
Os gorilas e os orangutáns,
por exemplo,
10:05
afford about 30 billion neurons
261
593540
1923
poden permitirse uns
30 mil millóns de neuronas
10:07
by spending eight and a half hours per day eating,
262
595463
2966
botando oito horas e media
comendo cada día,
10:10
and that seems to be about as much as they can do.
263
598429
3116
e isto é o máximo ao que poden chegar.
10:13
Nine hours of feeding per day
264
601545
1791
Nove horas comendo ao día
10:15
seems to be the practical limit for a primate.
265
603336
3271
parece ser o límite práctico
para un primate.
10:18
What about us?
266
606607
1791
Que hai de nós?
10:20
With our 86 billion neurons
267
608398
1600
Cos nosos 86 mil millóns de neuronas
10:21
and 60 to 70 kilos of body mass,
268
609998
3035
e 60 ou 70 kg de masa corporal,
10:25
we should have to spend over nine hours
269
613033
3561
deberiamos ter que pasar
unhas nove horas
10:28
per day every single day feeding,
270
616594
3575
comendo cada día,
10:32
which is just not feasible.
271
620169
2039
o que non é factible.
10:34
If we ate like a primate,
272
622208
1834
Se comésemos coma un primate,
10:36
we should not be here.
273
624042
2253
non estariamos aquí.
10:38
How did we get here, then?
274
626295
2127
Daquela, como chegamos aquí?
10:40
Well, if our brain costs just as much energy
275
628422
2735
Ben, se o noso cerebro
gasta toda a enerxía
10:43
as it should, and if we can't spend
276
631157
1723
que se supón, e se non podemos pasar
10:44
every waking hour of the day feeding,
277
632880
3674
todo o día comendo,
10:48
then the only alternative, really,
278
636554
1911
entón a única alternativa,
10:50
is to somehow get more energy
279
638465
1958
e conseguir, dalgún xeito, máis enerxía
10:52
out of the same foods.
280
640423
1953
da mesma comida.
10:54
And remarkably, that matches exactly
281
642376
3800
E, sorprendentemente, iso encaixa
10:58
what our ancestors are believed to have invented
282
646176
3037
co que se supón que inventaron
os nosos devanceiros
11:01
one and a half million years ago,
283
649213
1839
hai un millón e medio de anos,
11:03
when they invented cooking.
284
651052
2782
ao inventaren a cociña.
11:05
To cook is to use fire
285
653834
1970
Cociñar é usar o lume
11:07
to pre-digest foods outside of your body.
286
655804
3800
para predixerir alimentos
fóra do noso corpo.
Os alimentos cociñados son máis brandos e,
por tanto, máis fáciles de mastigar
11:11
Cooked foods are softer, so they're easier to chew
287
659604
2606
11:14
and to turn completely into mush in your mouth,
288
662210
2563
e de converter en papa na boca,
11:16
so that allows them to be completely digested
289
664773
2152
isto permítenos dixerilos completamente
11:18
and absorbed in your gut,
290
666925
1436
e absorbelos no intestino,
11:20
which makes them yield much more
energy in much less time.
291
668361
3655
o que fai que desprendan moita
máis enerxía en moito menos tempo.
11:24
So cooking frees time for us to do
292
672016
2489
Así que cociñar dános
tempo libre para facermos
11:26
much more interesting things with our day
293
674505
2062
cousas máis interesantes co noso día
11:28
and with our neurons
294
676567
1480
e coas nosas neuronas
11:30
than just thinking about food,
295
678047
1905
que pensar só en comer,
11:31
looking for food, and gobbling down food
296
679952
1704
buscando comida e engulindo
11:33
all day long.
297
681656
1225
todo o día.
11:34
So because of cooking, what once was
298
682881
2499
Grazas á cociña, o que unha vez foi
11:37
a major liability, this large,
299
685380
2353
unha carga pesada, este cerebro enorme
11:39
dangerously expensive brain with a lot of neurons,
300
687733
3033
e perigosamente custoso
cun montón de neuronas,
11:42
could now become a major asset,
301
690766
2036
puido converterse nun gran recurso,
11:44
now that we could both afford
the energy for a lot of neurons
302
692802
3251
ao poder permitírmonos
a enerxía para moitas neuronas
11:48
and the time to do interesting things with them.
303
696056
2503
e o tempo para facer
cousas interesantes con elas.
11:50
So I think this explains why the human brain
304
698559
1974
Así que penso que isto
explica por que o cerebro humano
11:52
grew to become so large so fast in evolution,
305
700533
3240
evolucionou tanto e tan rápido,
11:55
all of the while remaining just a primate brain.
306
703773
3897
mentres seguía sendo
só un cerebro de primate.
11:59
With this large brain now affordable by cooking,
307
707670
2774
Con este cerebro enorme que nos
podiamos permitir grazas á cociña,
12:02
we went rapidly from raw foods to culture,
308
710444
2913
pasamos rapidamente
da comida crúa á cultura,
agricultura, civilización, tendas,
12:05
agriculture, civilization, grocery stores,
309
713357
2606
12:07
electricity, refrigerators,
310
715963
1625
electricidade, refrixeradores,
12:09
all of those things that nowadays
311
717588
1607
todas esas cousas que agora
12:11
allow us to get all the energy we need
312
719195
2042
nos permiten conseguir
a enerxía precisa
12:13
for the whole day in a single sitting
313
721237
2782
para o día enteiro
mentres sentamos
12:16
at your favorite fast food joint.
314
724019
2954
no noso bar preferido de comida rápida.
(Risos)
12:18
So what once was a solution
315
726973
2437
Así que o que unha vez
foi a solución
12:21
now became the problem,
316
729410
1699
agora convértese no problema,
12:23
and ironically, we look for the solution in raw food.
317
731109
5517
e, ironicamente, buscamos
a solución na comida crúa.
12:28
So what is the human advantage?
318
736626
2556
Así que cal é a vantaxe humana?
12:31
What is it that we have
319
739182
1503
Que é iso que temos
12:32
that no other animal has?
320
740685
2535
que ningún outro animal ten?
12:35
My answer is that we have the largest number
321
743220
2348
A miña resposta é que
temos o maior número
12:37
of neurons in the cerebral cortex,
322
745568
1472
de neuronas no córtex cerebral
12:39
and I think that's the simplest explanation
323
747040
1844
e creo que é a explicación máis sinxela
12:40
for our remarkable cognitive abilities.
324
748884
2013
para as nosas extraordinarias
habilidades cognitivas.
12:42
And what is it that we do that no other animal does,
325
750897
3227
E que facemos nós que
ningún outro animal fai
12:46
and which I believe was fundamental
326
754124
1969
e que penso que é fundamental
12:48
to allow us to reach that large,
327
756093
3083
para permitirnos acadar ese número
12:51
largest number of neurons in the cortex?
328
759176
2222
tan grande de neuronas no córtex?
12:53
In two words, we cook.
329
761398
2215
En dúas palabras, nós cociñamos.
12:55
No other animal cooks its food. Only humans do.
330
763613
3566
Ningún outro animal cociña.
Só o fan os humanos.
12:59
And I think that's how we got to become human.
331
767179
2870
E penso que é así como
chegamos a ser humanos.
13:02
Studying the human brain changed
the way I think about food.
332
770049
2460
Estudando o cerebro humano cambiou
a miña forma de ver a comida.
13:04
I now look at my kitchen,
333
772509
1645
Eu agora miro a miña cociña
13:06
and I bow to it,
334
774154
1470
e inclínome perante ela
13:07
and I thank my ancestors for coming up
335
775624
1705
e doulles grazas aos
meus devanceiros por dar
13:09
with the invention that probably made us humans.
336
777329
1900
co invento que probablemente
nos fixo humanos.
13:11
Thank you very much.
337
779229
2132
Moitas grazas.
13:13
(Applause)
338
781361
6353
(Aplausos )
Translated by Carme Paz
Reviewed by Servizo de Normalización Lingüística

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ABOUT THE SPEAKER
Suzana Herculano-Houzel - Neuroscientist
Suzana Herculano-Houzel shrunk the human brain by 14 billion neurons -- by developing a new way to count them.

Why you should listen

How many neurons make a human brain? For years, the answer has been (give or take) 100 billion. But neuroscientist Suzana Herculano-Houzel decided to count them herself. Her research approach involved dissolving four human brains (donated to science) into a homogeneous mixture -- in her lab at the Institute of Biomedical Sciences in Rio de Janeiro, they call it "brain soup." She then took a sample of the mix, counted the number of cell nuclei belonging to neurons, and scaled that up. Result: the human brain has about 86 billion neurons, 14 billion fewer than assumed -- but intriguingly, far more than other animals, relative to brain size.

She suggests that it was the invention of cooking by our ancestors -- which makes food yield much more metabolic energy -- that allowed humans to develop the largest primate brain. She's now working on elephant and whale brains to test her hypothesis.

More profile about the speaker
Suzana Herculano-Houzel | Speaker | TED.com
THE ORIGINAL VIDEO ON TED.COM