You can hypothesize what you want. Science is there to test hypotheses and science says there are two genders.
I think it would help to clarify what you mean by gender from what others are using it denote. I understand your usage of gender as describing the sexes whose anatomy and behavior (at least to some minimal level) is regulated by biology. Others such as Brian seem to using it to describe the different roles we can express ourselves socially using the spectrum of human sexuality.