"I think the whole "is it natural" question is a dead end.
It harks back to old school thinking about "the natural order" and that you can divide human behaviour into natural and unnatural and use that distinction to condemn or discourage so called unnatural behaviour - "it is unnatural for women to lead" "lesbianism is unnatural" etc..."
I agree. It's very tempting to argue that X - lesbianism, bisexuality, extended breastfeeding... - is natural (in the 'occuring in nature' sense), because 'unnatural' feels like a hurtful insult, and indeed because many of those things arguably are natural, it's just that our perspective has been skewed by society. But, there's so many examples where natural things are clearly terrible, that it's a logical fallacy to condemn something because it's unnatural. Obviously we don't want to construct a society where everyone behaves like wild animals; I think focusing too much on natural vs unnatural, while scientifically interesting, tends to reinforce the flawed 'natural = good' idea.
On the other hand, it seems that many religious people have a whole different-again meaning for 'natural' which I don't fully understand... it would be great if someone religious could explain what they mean by 'natural'.