Men and women are different.
This self-evident and cliched claim is no longer as uncontroversial as, historically, it once was. According to a 2011 report from the American Psychological Association,
Gender identity refers to a person's internal sense of being male, female, or something else; gender expression refers to the way a person communicates gender identity to others through behavior, clothing, hairstyles, voice, or body characteristics ... Transgender people experience their transgender identity in a variety of ways and may become aware of their transgender identity at any age.[i]
This statement includes a reference to an undefined but apparently defining "internal sense" and the concurrent argument that one can recognize his or her transgenderism "at any age." Such an assumption has stunning implications for the way law, society, and family all function.
But before we examine that assumption, let's start here: what's the deal with exclusively male-female unions?
[i] "Answers to Your Questions about Transgender People, Gender Identity, and Gender Expression," American Psychiatric Association, accessed October 7, 2013, http://www.apa.org/topics/sexuality/transgender.pdf.