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.
I often bump into heredity theories based on genetics trying to show women are less brainy then men or show this etnic/race is higher or lower then others. its quite common. In fact a famous book called the bell curve was made about it.