Existential fallacy

Biological Parallel

'All unicorns have horns. Therefore, some unicorns exist.' The existential fallacy infers existence from categorical statements. In biology: 'All organisms in ecological niche X must have trait Y' doesn't mean niche X is occupied. Empty niches are pervasive—Australia had no placental predators before dingoes, despite the 'niche' existing. Evolutionary theory predicts traits for unfilled niches, but prediction doesn't guarantee actuality. Evolution is contingent, not logically necessary.