Why do different cultures develop different notions of personal space?

Americans sometimes have trouble going to Europe or Arab countries, because in those countries, the notion of personal space is different. They may not need as much of it as Americans do.

Why would there be a different notion of personal space across cultures? Is there anything you can think of that explains why these differences are what they are?

And, just for fun, what is your notion of your own personal space needs? My son is very lovey-dovey, and hugs and kisses all the time, while my daughter doesn’t like to be touched, and never hugs or kisses. I’m somewhere in the middle.