When I had a class in which I really didn't like the teacher, but really liked the material, I knew I had to do anthropology. Psych didn't do it for me. Bio didn't turn me on at all. I think that psychologists have the best experimental methods on the planet when it comes to lab stuff, but they often don't know zip about the natural history of the animals they study. Too much universal learning paradigm for me.
Anthropologists know it all - from the anatomy of the earliest primates, to that of living primates.
We ask questions about what monkeys eat, who is eating with whom, where they sleep, and who is sleeping around. Two reasons - one personal and one professional. In terms of the former, I had to go to the San Diego zoo as part of an assignment. I heard ruffed lemurs making this outrageous call and was fascinated. That's exactly how I got started.