Monthly Archives: February 2014

MYSTERIES OF THE BRAIN Part 25: What was the catalyst for the extraordinary evolution of our brains?


This is episode no 25 of the VERITAS series on the mysteries of the brain. Older parts can be found here:

In this part we will learn about a very important event that resulted in the remarkable development of the human brain. And it is this event that resulted in humans becoming so much more intelligent than other creatures which in turn has made us the dominant species on earth.

The question that we must answer first is this: if intelligence is good and if intelligence has an evolutionary advantage then why don’t we see all animals grow massive brains? I must tell you that there are some animals like bats whose brain sizes have decreased with time. The answer is simple: Brains are costly. When I say costly, I mean costly in terms of energy consumption. In bats the competition was between maintaining or growing a costly brain vs  the energy cost of flying. Evolution decided that flying is more important for bats in terms of ability to survive so brain sizes went down and precious energy resources were used for flying.

Therefore the  size of the brain is governed by the constant battle for energy. If a creature does not need a bigger brain for survival or does not have enough food to  supply the energy required by a bigger brain, then the brain size would not increase.

Now let’s answer the question: how much energy does a brain consume? Most animals have brains that take up 2% to 8% of their total metabolism. In human brains the percentage is much higher. An average human brain requires 20 to 25% of the total energy requirement of our bodies. So nearly 25% of the energy that we consume goes to our brains! This energy requirement is even more remarkable when we consider the weight of the brain- only 2% of our body. So the human brain is 2% in weight  but consumes 25% of the energy that our body consumes.

So if we make the statement that our brains are large because we have enough food to feed its energy requirement, we would not be wrong. But there is a deeper mystery. We have more food because our intelligence has enabled us to get surplus food. There was a time in history when we too lived in jungles like other animals and that time we too struggled for energy. So what caused our brains to grow? And to give you an indication of the growth: the human brain weight was about 400 gms about 3 million years ago- this is comparable to modern chimpanzees. Today the brain size of an average adult is about 1400 gms. So the question is : how did we manage to solve the energy problem required for a bigger brain? What is it that gave our ancestors the ability to get more energy thus causing rapid brain size increase?

The answer is simple: cooking. Our ancestors discovered fire nearly two million years ago and that suddenly changed the trajectory of the “human” race. Today we cannot eat most of our food raw and unprocessed. We do many things to it: we pound it, we grind it, we ferment it, we cook it. And all these things that we do to food improves the efficiency of energy that we extract from it. For example grinding and pounding makes the food particles smaller and it becomes easier for our stomachs to digest the food. However the biggest impact on energy efficiency came from cooking. A group of scientists did some experiments on mice. They divided mice into two groups- one group was given raw potatoes and the other was given the same quantity of cooked potatoes. After four days the scientists found that the mice that had been eating raw food lost on an average 4 grams . The group of mice that ate cooked food gained weight.

Cooking food breaks it down and makes it easier to digest – less energy is expended in digesting this food. In scientific terms, cooking causes a denaturation of proteins which causes some of its structures to break down and therefore more easier to digest.  Also since the food is digested better, we are able to get more energy from it. In addition, cooking kills germs and less energy is used by the immune system to kill the incoming germs. And as humans started eating cooked food, our guts started decreasing in size. So we saved the energy required to maintain a bigger gut. All these energy savings and the extra energy from cooked food meant one thing- we had an energy surplus. We could afford a bigger brain. And that is what we have now. We have probably the most expensive brain in the animal kingdom – one that uses 25% of our incoming energy.  But that’s okay because we have that extra energy to spare because of cooked food.

Cooking also had another effect that contributed to our rise. We wasted less time in eating. A giant panda spends upto 16 hours a day chewing bamboo. The panda nearly never eats anything else but the food that it eats is so difficult to digest that it has to spend every waking hour eating. It has no time for anything else. Pandas are not very social creature because even being social is time consuming and energy consuming. And the panda has no time to waste- it has to keep chewing all day to maintain its weight. Our primate cousins – chimps also spend nearly half a day eating food. Eating low calorie density food like fruits and bamboo shoots means that the creature has to eat for more time in the day. Carnivorous animals do better and have time to spare but not so much. Cooking gave us the advantage that we had free time for other things. An adult human spends only about an hour eating food in a day. And we are still able to feed our massive brains sufficiently. In fact the efficiency of our cooked food is so high that we are able to gain weight by eating only an hour in a day and even after feeding 25% to our brains.

Now let’s take a different view of the cooking theory. If you want to decrease weight you should be eating more of raw food or at least lesser processed food. Some studies have suggested that people who eat raw foods or unprocessed food ( like whole wheat bread etc) spend two times more energy in digestion as compared to people who only eat processed, cooked food. Also you will get less energy from raw food. So eat raw food if you want to decrease the energy consumed from food. However, do not apply this theory on kids. They need energy so cooked food is actually much better for them.

So the discovery of fire resulted in the extraordinary evolution of the human brain.

If you want to know more about the cooking hypothesis read the book “Catching Fire, How cooking made us human” by Richard Wrangham.

And to make your day( and mine) even more delicious here are some excerpts from a poem by Ogden Nash:

Some singers sing of ladies’ eyes,
And some of ladies lips,
Refined ones praise their ladylike ways,
And course ones hymn their hips.
The Oxford Book of English Verse
Is lush with lyrics tender;
A poet, I guess, is more or less
Preoccupied with gender.
Yet I, though custom call me crude,
Prefer to sing in praise of food.
Yes, food,
Just any old kind of food.
Some painters paint the sapphire sea,
And some the gathering storm.
Others portray young lambs at play,
But most, the female form.
“Twas trite in that primeval dawn
When painting got its start,
That a lady with her garments on
Is Life, but is she Art?
By undraped nymphs
I am not wooed;
I’d rather painters painted food.
Just food,
Just any old kind of food.


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Go wondrous creature, mount where science guides
go measure earth, weigh air, state the tides,
instruct the planets in what orbs to run
correct old time, regulate the sun
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