But is poetry itself not evidence for a human soul?
What other creature could produce or appreciate such abstract entities?
We cannot summon into existence an entire domain of previously undiscovered reality on the back of 'we like poetry'. That wouldn't count for evidence in any other context. A good understanding has to encompass all of life and all attempts to categorise humans as fundamentally different are bound to fail at some point as the entirety of our understanding from biology and genetics points to a continuum of related life forms built from the same organic principles through shared ancestry. Humans might appreciate poetry sure enough but that doesn't categorise us as somehow separate from the great tree of life, and if we care to look at the rest of nature we don't have to go far to find some development of aesthetic sense in other creatures. Flowers are beautiful aren't they, but flowers were beautiful long before humans evolved to wonder at them; natural selection wrought their beauty not for us but to appeal to bees and pollinating insects so we can infer that in the tiny brain of a bee, perhaps just a few million neurons, lies a primitive nascent ancestor of what has developed in us as a rich sense of aesthetics. I see hints of our relatedness to the rest of the animal kingdom everywhere, in our physiology, in our behaviours, in our experience, and all that richness of insight and wonder is lost in a view that holds humans as separate, cut off, unrelated, made of some undiagnosed supernatural stuff.