Why do good qualities tend to attract and combine together, is it genetics or lifestyle or something else?

Like when I went to school, most of the men and women I talked to were very good looking. They were also 90% or higher very intelligent.

I was watching a video of another school that has a lower ranking, and it seemed over 75% of the students were very overweight. Many had wrinkles on their face in their teens or twenties.

I went to a very good high school and when I google these people I went to school with, less than 8% are fat.

People who went to poorer high schools seem to have much higher obesity rates and health problem ratios.

Why do good qualities tend to attract and combine together, is it genetics or lifestyle or something else?
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