Vexing and Sarah-
You're both right- to a point. I will say that many of our society's expectations for people of each sex are purely constructed and artificial and that socialization explains how most stereotypical behaviors become what people are expected to abide by. However, I think there are sexually differentiated behaviors that generally align with biological sex. Obviously this isn't always the case as it ignores intersexuality and the many children whose biological "gender role performances", as it were (though it seems criminal to use that word, and I don't think it's really an appropriate label), do not match the socially acceptable performance. But it's impossible to ignore the fact that animals have behaviors that differ between the sexes, and humans are no different.
For example, chimpanzee boys will often tangle with each other and fight with sticks, while the girls frequently carry sticks and treat them like dolls or babies. These aren't products of social construction, obviously. In the same way, humans have some behaviors which are innate and differ between boys and girls. This isn't to say that the behaviors are absolutely differentiated, perfectly, all the time, but to say that zero human behaviors are innately male or female seems misleading, at least.