"How do you know? Perhaps it is because the areas Grizzlies live are devoid of climbable trees so they just don't get the chance? I bet given a chance a polar bear could shinny up a tree it it wanted to but again they really have no practice given the maritime enviroment within which they live. You want to ensure against grizzly bear attacks? Spray yourself with boiled human urine-the bear can't stand the smell and will give you a wide berth. Trust me on this one-In all the years I've used it, I have NEVER and I mean NEVER come across a grizzly in the marsh. "
Caj: Probably make good birth control, also! Ever have a woman come on to you while wearing your concoction in a marsh?
Actually, there is a biological/evolutionary reason for black bears climbing trees and grizzlies not. Biologically, black bears are often lighter in weight (not always), and have curved claws. Grizzlies have straight claws (for digging=that's the reason for the big hump between the shoulders. Polar bear bears are curved but in a different way (Caveat: I've only examined one set of polar bear claws) in order to grip the ice.
Evolution-wise, black bears evolved in the forest where trees were/are abundant. Evolution would favor female bears that sent the cubs up trees to safety over aggressive moms, whose cubs would get caught and eaten. Grizzlies evolved on the plains, without trees (They later fled mankind and retreated to the wilderness areas). Evolution favored the mothers who FEROCIOUSLY stood their ground! In each case, the mothers who survived would be most likely to pass their genes down.