Generally speaking, the size of an animal’s brain relative to body size is an indicator of how intelligent the animal is.  The average human brain weighs about three pounds and has a volume of about 1300 cubic centimeters, which, for the size of the human body, is a lot of brainpower.

The largest brain of any land animal, however, is that of an elephant which is about four times as large, but that brain must contend with a lot more body mass. The smallest brains, for instance those of worms, stretch the limits of what a brain actually is. In lower animals the brain is more like a collection of nerves, a sort of “cross-roads” that regulate the organism.  

Relative to body size, present-day humans do not have the largest brains. Our extinct cousins, the Neanderthals, had brains averaging 1500 cc.  The earliest anatomically modern humans, Cro-Magnons, also had brains on average 15% larger than modern brains. Studies of ancient human remains indicate the human brain was larger up until about 25,000 years ago. From that time forward the human brain has seen a more or less steady decrease in size.

If we look at the various human societies today, we find that East Asians have the largest brains relative to body size averaging about 10% larger than those of people of European decent. On average, men have larger brains than women.

So does the size of the human brain indicate some groups of people are smarter than others? Extensive testing does not support that hypothesis. For instance, there is no difference in potential intelligence between men and women even though women have smaller brains. Probably the size of the human brain has less to do with potential intelligence and more to do with what we do with it.

However, to many anthropologists the general decrease in human brain size over the last 25,000 years is a troubling sign. Are we dumber than our distant ancestors? Or is the brain shrinking in size because we don’t use it?

Should we be concerned for future humans?

Consider a couple points. The brain began getting smaller about the time humans began the transition from small groups of hunter-gatherers to larger congregations supported by agriculture. During pre-agriculture, which is also pre-writing, humans had to carry all life-saving information in their heads. If you weren’t up to the task, you likely didn’t survive to reproduce. There was a lot of environmental pressure to be as smart and clever as possible. The development of larger congregations of people and eventually city-states protected the less mentally endowed and allowed them to contribute to their society in a meaningful way. The invention of writing reduced the need for memorization. In short, people didn’t need to be as smart to survive and reproduce.

Modern man believes he is the master of nature, but ironically, the processes of evolution are at work in the human species. It is a subtle effect but all our conveniences and labor-saving devices and technological gadgets are rendering parts of our brain unnecessary. In evolution, it is a fact that over many generations, if you don’t use it, you lose it. 

And with AI (advance artificial intelligence) just around the corner, we won’t even have to think.

A life-long resident of northern Minnesota, Terry Mejdrich is a former math teacher and farmer turned mystery author and freelance writer.

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