John Jay Ray points me to this abstract titled Physical Aggression and Expressive Vocabulary in 19-Month-Old Twins. Interesting excerpt:

...A modest but significant correlation (r = -.20) was found between physical aggression and expressive vocabulary. Substantial heritability was found for physical aggression....

The heritability part for physical aggression is not surprising-generations of pussies beget pussies-but the correlation with expressive vocabulary is interesting, though it tends to be loud-mouths that pound the crap out of other kids from what I recall.