We may have poisoned the world first, but good old Earth got the last laugh. The human species is diseased, genetically decomposing from birth – each generation’s lifespan is a little less than the one before.

We’ve adapted. Of course we have, scientists and survivors all, this motley collective of mothers and soldiers and sick little children. When we’ve reached the point past which our bodies and minds begin to unravel like so much loose thread, we choose our fate and our future: an animal.

We get spliced. It’s a harrowing, intensive procedure that no one in their right mind or hale body would ever voluntarily undergo, but when it’s transformative surgery or death, well, the choice is a little easier. We pick an animal, and scientists and doctors mix their genes with ours.

We keep some necessary human attributes: opposable thumbs, vocal chords, diurnal vision, bipedal stance. We stay within a reasonable size range. Only mammals for us – reptiles, amphibians, and birds are left for the truly desperate, and insects and arthropods just don’t work.

If a person gets spliced early, they keep a little more of their humanity. Maybe all they have to deal with is a coat of fur, some claws, different ears, a tail. The sickest of us, well, we have less that’s worth keeping, so more animal gets spliced in. Some people can’t walk with their backs vertical anymore. Some people have completely animal faces, molded around a human braincase. Some people look like damn Hollywood werewolves, hunched and gnarled and desperate.

The more animal gets spliced in, the riskier the surgery, the higher the mortality rates. As it is, you only get a one in three chance of surviving and not rejecting the new hybrid genome. That’s purely physical, of course – everyone tries to ignore the odds of going insane after you heal. Or feral. We’ve got monsters roaming the tortured world that used to walk strollers down the street and shop at Walmart. And we all pretend that the ones who don’t go nuts are okay, but we’ve got new and burning instincts inside our half-human bodies, and our societies are fraying quickly with the pressure of being civilized.

Some humans – some rare, rare few – are immune to this genetic plague. They can stay human for what used to be a normal lifespan – seventy, eighty years – without dissolving into some hellish combination of leprosy and cancer. Scientists are working like mad to figure out what makes them different from the rest of us, the ones who have to get spliced to survive. They still have no idea.

They say it’s only a matter of generations before our lifespans are so short that… well, we won’t be able to pick an animal ourselves anymore. Parents will be picking species for their five-year-olds, and who knows if a kid can survive transformative surgery. The few that’ve needed it haven’t.

We’re sterile, of course, us spliced ones. Every human who hits puberty contributes sperm and eggs to the banks, hoping they’re donated before the disease really spreads, hoping those cells might turn into one of the unaffected. Extremists think it’s time to start turning our medical and scientific resources to making us hybrids fertile, rather than clinging to the last vestiges of real humanity.

Maybe they’re right, but then we run into a new, awful problem: can someone who is half-dog breed with someone who is half-goat? What do those kids look like? How do you mix bastardized genomes of entirely different species?

Some say we’ve doomed ourselves by allowing diversity, by allowing choice. We should have all been dogs, they say – dogs are the best choice, mentally compatible with humans, socially similar, physically familiar. But dogs are carnivores, and the world doesn’t have as many real animals to eat as it once did. A lot of us became omnivores or herbivores to keep the balance, to not bleed the earth dry of its children.

Maybe the human species is dead, and splicing is just a death throe. Those of us left are just a fraction of the billions that were here when the condition first began.

Or maybe this is the phoenix’s ash, and all we’ve got to do is hang on before we can fly again.