Why is every measurable Human quality run along a bell curve?

[Andy]

When you think about Human qualities, it runs along a bell curve, so to speak, where some people are greater at particular qualities then others.

 

[glenn123]

Because it's not about the human quality, but the nature of collecting data. A normal distribution like that will have an average quality to it, depending on what you are taking statistics on...and also have outliers. Bell curves are fairly normal IMHO.