At first I was like "The nature of Posting is that every so often somebody accidentally reinvents Mind Flayers"
but I was like "wait a fucking minute" because I remembered the FUCKING FORCEFEMMING CRAB CORDYCEPS BARNACLE
Goddamnit I think it's actually fucking biologically possible for a sapient species to evolve from something like this without knowing it I am so fucking mad.
Ancestral species with extremely basic nervous system exists
Vaguely related species evolves with free-swimming larva that metamorphoses into sessile ectoparasite
Ectoparasite evolves into mostly-endo-parasite that embeds parts of itself into host to siphon nutrients
Becomes Sacculina-esque endoparasite that infiltrates host's entire body.
Parasite takes over host's nervous system. Eventually replaces its functionality entirely.
One species of these parasites has a life cycle that happens to make it a selective advantage to keep the host alive and reproducing more or less normally. As a result it evolves to be better at being a nervous system that makes the host do normal things.
Being infected with the parasite actually gives the host a selective advantage despite its nutrient siphoning. The host evolves to more or less disintegrate its original nervous system after infection because the parasitic nervous system does its job better.
The parasite is now for all intents and purposes an endosymbiote, and both it and the host are dependent on one another. The parasites are specialized to specific host species.
The symbiote starts hiding its reproductive organs inside the host as well instead of having a massive blob of Externa. It starts having less need to spam massive amounts of eggs because it's so effective at meat-puppeting the host around that it can just attach its own eggs to the host's eggs whenever the host spawns. Male larvae attach to and fertilize female ones while they're waiting for host eggs to hatch.
The symbiote is still getting better at being a nervous system and continues to evolve in parallel with morphological and lifestyle changes to the host.
Life on land is a still a challenge. Externally fertilized amphibian / land crab analogues are fine, but the larvae are still technically free-swimming. Until one makes the evolutionary leap of burrowing into the egg and infecting a developing embryo.
At some point a lineage of internally fertilized hosts develops with a parasite species that hides its externa inside the host's reproductive tract. Symbiote larvae now hatch inside the host as well and continue to feed off their parents' externae until the host copulates / ovulates, at which point the ones from a male host hitch a ride with the sperm (both male and female larvae present) and the ones from a female host hang out inside the uterus. These meet and spawn, the male larvae die, and the female larvae wait around until they can implant themselves into fertilized eggs.
It is now possible for amniote-analogs to develop, as embyros are pre-infected with a symbiotic nervous system before the waterproof eggshell forms.
Vivipary can also emerge in the hosts: the symbiote larvae just hang out in the uterus until they're needed.
Hundreds of millions of years of evolution go by. Adaptive radiation etc. The symbiotes are by now specialized to differentiate most of their cells into basically neurons, and develop centralized masses of tissue + hijack the host's body to feed them with blood vessels the same way cancerous tumors can force the body to give them a blood supply. The centralized nerve clusters are so vital to the host that the host has long since evolved to protect them.
The symbiotes are by now conscious in their adult form and have no memories or conscious awareness of the larval stage.
Much much later, one species of symbiotes develops a technological civilization. They are fundamentally unaware that their "real" body isn't the host organism.
Nobody notices anything until microscopes are invented. Dissection of cadavers obviously reveals the internal symbiote "externa" (technically on the outside of the host's body because the uterus / vas deferens are on the outside), but they just look like some relatively normal looking glands. The symbiote larvae are much larger than actual sperm and multicellular, but still too small to easily detect. Even then, what biologists first think is that there are two types of unusual gametes that both sexes produce, and that are only present in the same phylum as People.
It's not until genomes are sequenced, and biologists identify less derived forms of the symbiotes with more obviously independent reproductive cycles, that anyone really starts putting the pieces together. Somebody sequences the genomes of nerve and brain tissue, the mysterious glands in the reproductive tract, and ejaculate, and finds that they are completely different than somatic and gamete cells. Not even close. Not even the right chromosome count, but oddly similar considering that. Also identical twins are only genetically identical in the somatic parts of their genomes, their brains are as related as siblings should be about half the time (both nervous systems developed from female offspring of same host-parent's nervous system) and totally unrelated half the time (one twin's nervous system is the mother's offspring, the other is the father's).
Entire world is in an uproar. Certain unsuccessful birth control pill attempts that "work" if taken very quickly after sex but result in a short failed pregnancy and spontaneous miscarriage of a fucked up fetus with no brain or spinal cord suddenly make sense: they fucking kill the larval symbiotes in the patient's uterus!
Discourse shitstorm of epic proportions ensues when some smartass points out that technically everyone is female because a person is actually a symbiotic organism meat-puppeting a body, and only the female symbiote larva implants into a host embryo. Several major religions undergo schisms.
I know you were shitposting OP but I feel like a fucking Lovecraft protagonist knowing that it could, in theory, be possible that on some planet somewhere the equivalent of this ridiculous biological atrocity of a barnacle could become a species of beings smart enough to have an existential crisis when their technology advances enough to discover their own chimeric nature.
blakekathryn
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