Brain #1: Purpose and Optimization

For what purpose has the brain evolved? As humans, we are biased when we encounter that question, writes Lisa Barrett in Seven and a Half Lessons About the Brain. We wrongly assume that the purpose of the brain is to think:

“After all, thinking is the human superpower, right?”

 

Wrong, says Barrett. Long, long ago, unicellular life found itself in competition with others over limited resources, the importance of any capability to sense what lay where was an evolutionary advantage – Did XYZ lie to the left or right? Gradually though, raw sense organ signals weren’t enough. Choices had to be made – was it likely one could catch the prey? Make a wrong choice repeatedly and one would die of starvation. Thus:

“Energy efficiency was a key to survival.”

 

So Barrett concludes:

“Your brain’s most important job is to control your body… by predicting energy needs before they arise so you can efficiently make worthwhile movements and survive.”

 

But this created a new problem: the brain itself consumed energy. Thus, there was a tradeoff between how much energy the brain consumed v/s the benefits the brain control decisions yielded to the organism. Hence, optimizing the brain’s own usage of energy became an evolutionary need.

 

One such optimization was to predict rather than to react. Prediction in turn works better if the brain has memories to refer to. With a twist:

“Your past experiences include not only what happened in the world around you but also what happened inside your body. Was your heart beating quickly? Were you breathing heavily?”

 

Barrett then gives a daily event as an example:

“Think of the last time you were thirsty and drank a glass of water. Within seconds after draining the last drops, you probably felt less thirsty.”

A perfectly ordinary event, right? But guess what, there’s prediction in it!

“But water actually takes about twenty minutes to reach your bloodstream. Water can’t possibly quench your thirst in a few seconds. So what relieved your thirst? Prediction.”

 

Like all attempts at optimization, the brain’s evolutionary preference to decide based on memories too leads to problems. Is this one such instance:

“This may be one of the reason why people sometimes fail to empathize with people who look different or believe different things… and why it can be uncomfortable to try. It is metabolically costly for a brain to deal with things that are hard to predict.”

The book is interesting throughout and a fairly short read to boot.