Tyler Cowen at Marginal Revolution posts today on two biases:
We think we perform better in front of supportive audiences, but actually "we perform better in front of strangers or even a hostile crowd."
We rate people better if they share our birthday.
And Tyler privately mentioned:
In sports and fashion, smiles signal low status, not happiness.
The Dalai Lama smiles a lot.
Smiles signal low status if you define low status as the status of those who are smiling in this study. So bigger football players don't smile as much as smaller players. Their positions are different. Linemen are like sumo wrestlers needing to apply sustained, maximal power to every play. It's hard to smile and do that. Plus your intimidation is in your face as a lineman. As a back it's in your moves, your actions. Defensive backs get to run like the wind and point to a moment of attack when they see if they can take an opponent's head off. Then they can relax and look back, with a smile if they came close enough to actually doing that. Just look up how Jack Tatum of the Oakland Riaders used to talk about this. I'm sure he was smiling the whole time he talked about it with his joyful memories of really hurting someone. But he wasn't smiling at the moment of attack. You can't smile and give it your full force. That's why linemen don't smile. Maybe there are off-the-field reasons for the different faces,too. I'm 6'3". I've noticed the joy of looking down on people and not smiling. It's not good to do that all the time, but it's a nice option sometimes. I'm sure there are many factors in this and with the models that are poorly summarized as "smiles signal low status". People smile when they're free to smile and feel like it. Maybe there's an additional payoff for smiling or for scowling sometimes, but this study just conjectures about that instead of nailing that down as the cause of the observed behavior.
Then even if smiles were a signal of low status, they still could mean happiness, too. You'd have to find out how the subject experiences it. A smile can mean fear. A scowl can be joyful. Or vice versa for both. There certainly is a bias toward making simplistic conclusions about human behavior. We are not simple creatures.