Derby, so sorry you are having to have this discussion - I have been caught in a few of these and often I just end up thinking "what's the point?" The whole nature vs. nurture thing, as if it being in our DNA somehow makes it more "right". Then you get those that start going back and looking at what the cavemen did, as if THAT was somehow more justification for our nature.
How does the mono-to-poly scale help show whether or not it is biologically innate in us or not?
I saw similar discussions around the whole gay/bi/straight thing, and I just don't see how it can ever really get resolved by talking about it, or what use it is. The only way to prove it would be in a highly controlled way - identical twins, brought up separately, one in a mono environment, another in a poly environment. You would need control experiments and enough examples so that the results could be considered statistically significant.
Anything else, to me, is just psuedo-intellectual wank.
"Listen, or your tongue will make you deaf." - Native American Proverb