Thanks Giles, I think you had a very good approach to stick to things which the WT has no sensible comment on, namely the evidence for evolution in atavistic organs etc.
If as schoolchildren we had all studied the geological 'column', i.e. the sequence of deposits in the earth's crust which records amongst other things the development and divergence of living things from common ancestors, it would be difficult to avoid the facts of evolution.
However humans are not fact processing robots, we have feelings which are easily swayed by the behaviour of our community. With emotionally focussed religious salvation at Armageddon in mind, JWs happily suppress and dismiss factual evidence for real things such as Darwin's big idea.