Well, a lot of people like physical activity in a partner -- it says something about physical attractiveness, and also a sort of energetic outlook.
As for the predominance of outdoorsy activities -- honestly some of it is a class/culture thing, but so what. I've also noticed that there's overlap between math and mountaineering -- sort of the same kind of "coincidence" as math people liking Bach. Geeks tend to be drawn to physically demanding individual pursuits: running, climbing, cycling, and to a lesser extent weights. (Swimming ought to qualify but I've never met a lot of geeky swimmers.)
I see, that's interesting. (I run and swim - but swimming is very popular in my area.)
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