As far as I know, there is no scientific evidence for what I’m about to claim. This is just what I’ve been thinking.
I don’t know how long it’s been since you’ve been in a biology class, but do you remember how there are 23 pairs of chromosomes that make up our genetic information? The 23rd pair are the X and the Y that determine our sex, male and female.
I strongly believe, in fact I am firmly convinced, that somewhere in those 23 chromosomes lies the common sense gene. Everybody has one. However, for some people, the common sense gene just stopped growing. It never bloomed.
You know what I mean. You’ve seen them. Those certain people that do things so incredibly ridiculous that you end up shaking your head in disbelief.
That’s it. People that display a lack of common sense – it’s not really their fault. The gene didn’t bloom.
The Physics of Common Sense 