How does sumner differentiate between the "natural" roles of men and women in society?

I hate when people use the term "natural" in conjunction with roles for people. If it exists within nature, it's natural. There is no unnatural role for us. Unnatural would be growing wings and shooting fire balls from our eye sockets. It won't happen, because it's unnatural. However, men can be nurturers, while women can be protectors because it happens and it's natural. That's the difference.