I long ago heard this too and thought it stupid.
It couldn't be still generally a opinion because greatly I read always them going on about ethnic/race/sex intelligence comparisons based on brain size or brain this or that.
Yet if our brains were only 10% used then racial/sex theories would have no basis. tHese theories are based of coarse on evolutionary presumptions.
The bible teaches man has a soul and thinks with his heart. not his mind or brain.
The brain is merely a container for a thinking person.
probably its mostly to run the body and maintain memory.
Science fiction is wrong. brain size is unrelated to intelligence.
In fact I'm confident retardation is only a interference with memory.
Its just so wrong to see that our brain is our thinking ability.
Its just a machine with details to assist our innate thinking being.
We are made in Gods image and with his thinking ability.
nothing to do with a mechanical world.