Grizzlies are much more aggressive than black bears, due to evolution. Because of their long claws and shoulder hump, grizzlies can't easily climb trees to escape a threat (black bears can and do climb trees). Instead, grizzlies stand their ground. Mother grizzlies are particularly aggressive. Experts believe this aggression is linked to the fact that grizzlies tend to produce only six to eight cubs in a lifetime, compared to black bears that rear 12 or 13 cubs. Additionally, black bear cubs only remain with their mother for about a year, while a grizzly's cubs won't cut the apron strings for up to three years.
Tags: Bears, Black, Grizzlies