"Nor will this Earth serve him; he sinkes the deepe
where harmless fish monastique silence keepe,
who (were death dead) by roes of living sand
might spunge that element and make it land."
—John Donne, "Elegie on Mistris Bulstrode"
John Donne reminds us of a natural fact that most of us would rather forget: the necessity-of death. On this earth, life without death would be poetry without rhythm: limitless and therefore pointless. Without sex and death, life might have evolved into one great super-organism, immortal as well as immoral, resembling the modern pantheists' conception of Gaia, the vast living eco-system and planetary consciousness of which each human individual is but an infinitesimal part.
Donne was no pantheist but a Christian whose respect for harmless fish would have been limited to their edibility and their symbolic utility as an anagram for Iesous Christos Theos Soter. The proliferation of fish qua fish (or condors qua condors) has little appeal for any Christian less tender-hearted than St. Francis, who preached sermons to birds and addressed the fire that burned his flesh as "brother."
"Mere existence" of any kind, for the Christian, is never the issue, though a fearful Samuel Johnson once declared...