God’s good design [is] that gender identity is determined by biological sex and not by one’s self-perception..."The way this issue is framed by the SBC is representative of the way I've heard many people discuss it. (And by the way, the only reason I am picking on the SBC is because my own church, the UMC, strangely enough, doesn't even have one line in the Book of Discipline about transgender persons. Which may actually be a good thing.) On this account, being a transgender person is about letting your own psychological self-perception take precedent over biological sex, and that is dishonoring to God who created you to clearly be a male or a female person.
Biology vs. Psychology?
This way of framing the issue, though, is problematic. While it is popular to say that "gender" (masculine and feminine) is a fluid psychological concept largely determined by culture, and "sex" (male or female) is a purely biological concept that is fixed by nature, this overlooks the fact while "sex" is a biological category, how we go about determining a person's sex is far from a biological given. Just ask Olympic's officials, who have engaged in several controversial decisions based on differences of opinion on what makes for a male or a female person. Is it chromosomes that matter? (But some intersex persons do not have the "normal" XX or XY patterns.) Is it internal reproductive anatomy that matters the most? External reproductive anatomy? Neurological structures? Hormone levels?
"Sex" is a biological category, yes, in that it depends on biological factors, but how the decisions are made as to what really counts to determine this category is a philosophical process, not a mere biological given. Biology alone cannot tell you what biological factors count the most for what "sex" a person really is.
Why do many people assume, without argument, that chromosomal make-up and/or reproductive anatomy is more indicative of a person's "true sex" than their neurological and hormonal features? While the origins of transgender identity are not clearly understood, it seems that most would agree that it is largely shaped (if not completely determined) by mostly neurological and hormonal factors. This means it is dangerously misleading to contrast, as the SBC resolution does, one's "biological sex" with "psychological self-perception," precisely because one's psychological self-perception is largely rooted in biological factors such as hormone levels and brain structure. Transgender identity, then, isn't simply about psychology versus biology. It's about a tension or discord between different biological factors that go into sexual identity (hormones and brain structures may not match up with chromosomes and/or reproductive anatomy).
"Male and Female"
Now to the issue of how to read Genesis 1:27. Contrary to modern myths about the inevitable and ongoing conflict of science and religion (propagated by both religious and atheist fundamentalists), there is a long tradition in the church of trying to integrate scientific understanding and biblical interpretation. This means most Christian bodies have found ways to interpret the significance of Genesis for us that do not deny what science has clearly revealed, such as the fact that the earth, contrary to the assumptions of Genesis, is not a flat disc in a geocentric universe covered by a solid dome holding back waters from the heavens (Gen 1:6-8; Psalm 148:4).
I would suggest that the new scientific information we have about transgender and intersex persons be treated in the same way as the new scientific information we have about the cosmos. How we interpret "God created them male and female" needs to accord with the best scientific understanding we have available to us. Just as the author of Genesis assumed limited and mistaken views of the cosmos (and yet God accommodated to that mistaken world view to reveal important truths), he also mistakenly assumed that biological sex determined both a heterosexual orientation and a certain gender expression. There are solid scientific reasons to now question these assumptions, and as Christians we should feel no more threatened by this than we do by Copernican cosmology. It turns out that understanding what is within us is just as difficult, if not more so, than understanding what is above us and beyond us.
The Traditional View?
We should also be aware of how historically contingent and recent our own "traditional" views probably are on what "male and female" mean. We often take that to mean an absolute polarity, an ontological distinction, a total difference in kind. Historian Thomas Laqueur, though, in his book Making Sex: Body and Gender from the Greeks to Freud, shows that much of Western intellectual history assumed a "one-sex model" of humanity, meaning that there is basically one sex with different bodily expressions. Basically, the male is the perfect form of the human sex, and the female is an imperfect form (surprise surprise!), and her anatomy and physiology were construed accordingly: the vagina is seen as an interior penis, the womb as a scrotum, the ovaries as testicles. Women were basically understood as having inverted male anatomy.
Sex, then, was not seen as an absolute dichotomy as many of us tend to see it, but as a spectrum of variation. This, at a minimum, should cause us to think about how on the "traditional" reading we might be importing modern cultural understandings of sex and gender into the Genesis text without even realizing it.
Why This Is More Important Than the Universe
While I compared changes to our understanding of sex and gender to our changing understanding of the cosmos, there is one big difference. You can believe that the earth is flat, 6000 years old, the center of the universe, and all that, and you probably will not do anyone any harm (unless you have kids and make them believe that too). But if you believe that transgender or intersex people are inherently deficient because of what you think Genesis teaches, you will do a good number of people harm, either directly or, more likely, indirectly.
You may not bully or beat up a transgender person, but you will help contribute to a culture that stigmatizes such persons, making them more susceptible to violence of various kinds. While violence against transgender people can't be blamed solely on Christian teaching, it also can't be denied that our teachings on this matter have often functioned as the soil in which seeds of hatred and violence have grown.
In short, we have a long history of adapting biblical understanding to scientific discovery. There is no reason to stop it now, and 226 reasons from this past year to keep it moving forward.