Gender is not always clear cut. One out of 100 babies has questionable genitalia, and one out of 1,000 result in surgery to the baby. Some people are XXY, or XYY, and there are other variations that don't always stand out. We don't yet test everyone genetically, nor would we fully understand what those tests would mean if we did. Perhaps some day we will. But we should make sure now, that genetic testing cannot be used to deny equal rights to all persons.<quoted text>
Proof would be something measurable- i.e. some physical finding.
Without that, there is simply no way of knowing whether it's not simply a delusional state?
To me that's the only relevant question.
But surely you have noticed a wide range in what we think of as "gender" among all men and among women? People don't look or act the same even if they are clearly men or women, and with many, it isn't that clear.(Especially as we age) That should be enough to realize we should let people see and express themselves as they wish as long as it doesn't harm others. Gender identity doesn't harm others.