Groupthink is a mythology like druidism or witchcraft that rushes in to fill the vacuum between the ears of people who are incapable of thinking.
They sit alone.
Nothing seems to happen. They start to get bored. The silence in their mind is deafening. This instrument without external stimulus begins to rapidly unravel. They have no internal dialogue. They squint and sweat. Nothing seems to be happening.
They give up and call a meeting. Now people are socializing and talking. That's even better than thinking, Sapiens feels.
Homo Sapiens thinks this is where the civilization he sees all around him came from. People on committees passing resolutions.
Subtract the Neanderthal and you have a bunch of monkeys in manpants sitting in the dust eating turd sandwiches and arguing over who gets to be alpha male. For hundreds of thousands of years without change.
Sapiens can't think. It's the Neanderthal with the rich dreamscape inside. The endless internal dialogue, more fascinating than a hundred channels on cable. Questioning. Arguing the viewpoint of his opposition. Counterarguing. Moving through a field of dreams, memories and ideas. It never ends and yes, sometimes you want to turn the volume down. You can't. The inside of your head is another universe.
Neanderthals are like this.
Sapiens is just a flat stare at the horizon and so much quiet in his cerebral tissue you could hear a pin drop. No dreamscape in there.
See why Sapiens could never amount to anything? He's a gregarious, highly social extroverted animal who gives the appearance of a variety of activities. In reality, he is no brighter than a shiny red button. Jacob without Esau would sit on his haunches, eat his meat raw, know no law but tooth and claw. He enjoys his beer, likes spectator sports (cathartic substitute for tribal combats) and sometimes dreams up little social schemes. Other than that, he is a terribly empty creature who simulates a real human being ... but is only a shell that mimics a man.
Without Neanderthal to hate in the past, the present and in the future, he would not even have any genuine rivalry. No passions, no love, no hates, no anything.
Just the terrible oblivion where his soul is supposed to go. The emptiness. The emptiness. At his core is a collapsed black hole from which not even light can escape.