with no one part able to present conclusive scientific evidence to prove their beliefs or disprove thier oponent's, the debate can only ever be hypothetical. This therefore allows a totally freeform debate where any party's evidence - being inconclusive - is not accepted by the other. In order to prevent the entire process from descending into farce, keep youself focussed on the topic i hand. See the topic, be the topic.
'I don't care what you believe; you have to admit that beliefs are odd' the late, great, Bill Hicks.