1. You learn from mistakes
  2. You read for fun
  3. You can argue from multiple perspectives
  4. You think before you speak
  5. You don't care what others think 

Note how four of those five factors simply don't apply to gammas who like to consider themselves highly intelligent. If you are a gamma male who refuses to admit mistakes, only argues from your current point-of-view, reacts emotionally and incontinently to criticism, and observably care deeply about what others think of you, what are you telling others about your intelligence?

And before anyone tries to get pedantic, note that if you refuse to admit your mistakes, you are most certainly not learning from them.

The fifth factor may explain why Sigmas tend to be more intelligent, on average, than Gammas.