John Richardson left a comment on an earlier post which I've been meaning to respond to - and now Bishop Alan has written on a related topic. It's unusual to disagree with John and +Alan on the same grounds, but there you go!
John writes: "I would have thought it was biology, rather than theology, that keep sex and procreation together, but this should affect our thinking about 'sexual relationships', especially where, in effect, they are not." +Alan writes: "Concepts of “natural” and “un-natural” are very fundamental to where people position themselves about homosexuality. There seem to be two basic perceptions from which everything else flows. As clearly and charitably as I can put it Either Homosexuality is a phenomenon against nature, and defies Creation and/or evolution Or Homosexuality is a phenomenon within nature, and thus part of Creation and/or evolution".
It seems to me that a properly Christian pattern of thinking needs to be careful about importing secular assumptions unnoticed when discussing certain scientific conclusions. That is, from a theological point of view, there is no neutral 'biology' from which we then draw theological conclusions; nor is there any mileage in the word 'natural'. Put differently, a properly theological perspective has the capacity (not the necessity) of construing the biological or the natural in a way that runs against any particular scientific consensus about 'facts' and, sometimes, it is obliged to do so. (This is essentially Milbank's point in Theology and Social Theory, although I think Wittgenstein got there first.)
I'll talk about the 'natural' first. The major problem with use of the word 'natural' in any discussion like this is that it cannot be given any substantive content. That is, human beings are themselves part of any 'natural' order - and so anything which human beings do is therefore 'natural' and the word loses any distinctive purchase. Alternatively, the distinction is drawn between the 'natural' and the 'human', in which case nothing 'human' is 'natural', and again the word loses its distinctive purchase. What use of the word 'natural' tends to be employed for is some sense of 'this pattern of activity aligns with this purpose' - that is, the substantive content of the word 'natural' when used in an argument derives entirely from the underlying aim envisioned for the human being, and it is at that level that the debate needs to engage. So, in matters of sexuality, one position envisions human sexuality as being entirely about procreation - this is what gets privileged as 'natural' - and therefore anything which is not procreative is proscribed as 'unnatural'. Alternatively, human sexuality is envisioned as being about pair-bonding and mutual affection etc, and therefore a much larger variety of sexual expression is 'natural'.
One way of progressing the debate might therefore be to enquire as to what is the actual 'biological' truth - is it the case that human sexuality is entirely about procreation, or not? Is it the case that, as John infers, it is 'biology' that keeps sex and procreation together? Where this aspect starts to break down, for me, is that it ignores the cosmic dimension of the Fall. That is, in Christian thinking, there is a distinction between the world that God originally made, and the world that we now inhabit. The latter is a broken or impaired form of the former, one that is slowly being redeemed and healed as we head towards the Kingdom. To say that it is biology that keeps sex and procreation together - if it is to do anything more than simply point out that (so far) conception is a biological process - does not advance our understanding very far. To return to the question of gay relationships, it is perfectly possible to say that homosexual attraction is a part of the evolved order in which we find ourselves, but to describe that as being part of the cosmic Fall. In other words, it doesn't actually advance the case in favour of gay relationships to point out all the ways in which there are gay relationships elsewhere in the existing order. It is perfectly possible for someone to say 'yes, that's true, but that's just evidence of our brokenness - it is not part of God's original intention and one day it will pass away'. (This relates to the ethical question about how to proceed if there was a 'cure' for homosexuality.)
There seems to be a distinction, therefore, between how something might be 'as God intends' and how things presently are - and from those to how we are to behave within our present context. I don't believe that appeals to 'biology' or what is 'natural' actually progress the discussion in a more Christian direction. What would do so, I believe, is if Christians began by pondering the rest of +Alan's post, most especially the shocking vitriol hurled at him for putting his head above the parapet on one side. If it is by their fruits that we will know them, then that is probably a much more certain place to start our considerations than any questions of biology or naturalness.