ONE of the best attended lectures - "Sex and the Brain" - revealed the humble vole could help settle the "nature or nurture" debate. Dr Ian Mitchell, from Birmingham University, told a packed theatre that brain differences could explain differences in gender behaviour better than social factors. He cited the prairie vole which is monogamous and has "all the attributes of a good husband". But in the non-monogamous montane vole, the hippocampus, part of the brain, is larger. This is vital in memory, so allows it to seek out females.