What’s special about a human brain?

Spoiler alert — it’s our ability to cook

Day 23 / 365

What’s so special about our brains? There are millions of species on this planet yet no one has cognitive abilities like us. Hell, they aren’t even close. Is our brain structurally different than every other species on the planet?

A few decades ago scientist used to think that all mammalian brains, including humans, were made the same way, and that the number of neurons was proportional to the size of the brain. Larger brain meant more neurons and therefore a higher intelligence.

This theory, however, has some obvious issues

• Brains of same mass don’t always imply a similar level of intelligence. A cow and a chimp both have brains around 400g in weight, yet chimpanzees show much more complex cognitive behavior than cows.
• Our brains aren’t the largest. Elephants have brains 4–5 times larger than us, but that doesn't translate to a larger intelligence.

So the size of our brains alone doesn’t explain it. There are other factors that make our brain special

Our brain is too big for our bodies

An average gorilla brain weighs about 0.5 kg, while an average human brain is 1.2–1.5 kg. This is the same with other great apes as well.

Our brain uses a lot of energy

Our brains weight is only 2% of our body weight, yet it consumes 25% of all the energy spent by the body. 1/4th of all your energy requirements, just to keep the brain running.

Intelligence and number of neurons

Suzana Herculano in this Ted Talk suggests that the number of neurons in brains doesn’t increase proportionally with size. A chimp’s 400g brain has a larger number of neurons than a cow’s brain, which leads to its increased cognitive abilities.

Human brains have around 86 billion neurons, way larger than other primates. This explains the high energy consumption by our brains too. The more neurons, the more energy we need for the brain to run.

The high energy costs are also the reason why large primates have smaller brains. A larger body requires more energy to function as well, so a larger brain that burns a fourth of all your power is just not feasible.

How cooking helps us to sustain these enormous brains

If you do the math, a primate that eats 8 hours a day can afford at most 53 billion neurons, and that is when it weighs just 25 kg. To weigh any more it either has to give up neurons or eat for more hours every day. How are we able to sustain 86 billion neurons with a 65kg body?

The answer is that we cook our food. We are able to extract much more energy out of the food we eat in much less time. Cooking also makes the food softer and easier to chew.

So that’s the human advantage. Once we learned how to cook our food it allowed our brains to grow bigger and denser in neurons, which gave us are remarkable cognitive abilities.

This story is part of my 365 Day Project for 2019. Read about it here

Yesterday’s blog — A rare galaxy that challenges our understanding of the universe