Genetic Synonyms

"They were a silly dying breed,some of them consumed with stopping the other half from destroying their planet,while all along they themselves were dying. We watched from a distance as they destroyed and killed,all the while wonder if they knew of their horrible condition that had consumed their race. Yet we sat watching in fear that by coming into contact with them, we too would become 'Death Breathers' and slowly kill off our race in ignorance while our own planet is infested with pollution and violence. "
What if the one thing humans need to live was toxic to them? oxygen, of course it takes 75-95 years to work but slowly the one thing that everyone needed was poisoning our otherwise long lifespan. And we lived in blissful ignorance. Never knowing how soon our destruction was.