Radio 4 this morning was discussing the case of a nudibranch (sea slug) which is hermaphrodite. That is to say it is both male and female. They both have both male and female organs. They both produce both sperm and eggs. When they meet and mate, they both inseminate the other.
On Genesis, we read that God made them ‘male and female’. This is the basis for the doctrine that in marriage it is required for a man and a woman to be united to become ‘one flesh’.
One must be careful drawing lessons on sexual morality from nature because animals exhibit every variation imaginable. But what I believe the nudibrachs teach us is that it is not necessary for all of the ‘male’ to be confined to one individual and for all of the ‘female’ to be confined to the other. The ‘male’ and the ‘female’ can be distributed across both individuals. In fact, my understanding is that all of us are on the same spectrum of gender, mostly concentrated at the ends in predominantly male and predominantly female individuals, but all of us have characteristics of the opposite (eg we all use both testosterone and oestrogen). Gay and transgender people are those at other positions on the same spectrum.
So in any marriage between any two individuals, both male and female will be represented across the two, and so the one-flesh image of God will be complete and complementarity will be satisfied.
And finally, if it says ‘God made them male and female, presumable I am one of the ‘them’, and so one could say that God made me male and female. And so I am no different to the gay person who is also male and female.