female genitalia = female identity = feminine behavior = desire male partner
male genitalia = male identity = masculine behavior = desire female partner

The other question is I guess is the topic of intersex and transgendered relevent to the same sex marriage debate?

Also if anybody has something interesting to add could you put in a couple of links, cheers.

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"Religion is excellent stuff for keeping common people quiet."
--Napoleon

If I grow a set of tits and remove my balls, can I marry a dude? Where's the cutoff?

It's all nonsensical, really. Just holding on to the last scraps of bigotry before realizing that it's the end to an era.

A useful link to start exploring ambiguous genders.

The premise that gender is not distinct is quite interesting if you consider gay marriage. What occurs if two people who are genetically 50/50 male/female wish to marry? Would one be required to consider them self a male while the other a female in order for them to marry? Would these individuals just not be permitted to marry unless they both had intrusive surgery to physically alter their genitalia?

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Here is a simple question in response then.

How do you know what prison to send a criminal to?

How do you know if they go to the men's prison or the women's prison?

How do you know what to sign up for with the olympics, men's gymnastics or women's?

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How do you know what prison to send a criminal to?

How do you know whether you should sign up for men's or women's gymnastics?

Amusing that you have the arrogance to think answers to such questions are so simple when opinions within the scientific community are and have been divided for centuries. It is hard to just find a consensus yet alone a definitive answer.