FWIW, at the one interview I have attended so far, one of my two interviewers, who was an adcom member, commented very positively about my majors. I think having more than major can only help you if:
1. it doesn't lower your GPA by more than a negligible amount. I consider .01-.02 to be negligible in most cases.
2. you don't have to take an obscene number of hours every semester to do it. The hours themselves don't matter so much, but rather that is time which you could otherwise have devoted to developing EC's.
3. the majors are in completing different fields. The more different the better, bio/anthro is a good but not great combination for this. My majors were about in that same range of difference. Much better than two science majors but not as unique as a science/arts double major.
Of course you shouldn't get an extra major unless it is really something you want to do. There are a lot of easier ways to improve your application.