Bats with Baby Faces: an Introduction to the Core Issues of Chimeric Hybridization and Related Interventions
Here's a brief introduction to surgical chimerization and affiliated biosculpting techniques from The House of Forbidden Knowledge's Professor of Undead Biology and University Chair of Radical Praxis.
The principal mechanism that causes problems when you graft a lump of tissue from a toad into a human being—to choose an example at random—is immunological at the core. When people speak of “tissue rejection” after a graft is stitched into place, they’re talking about the recipient’s body’s trained immune system not recognizing the proteins of the donated material and treating the attempted graft as it would any other infection.
This defense isn’t universally successful. Many, many foreign entities invade a human body with impunity. Some of them we count on for enabling and aiding various kinds of digestion. Some of them are parasites, long used to shrugging off attacks from leukocytes and other attempts of a human body to make the environment unlivable. Some have merely evolved to be made from a suite of proteins similar enough to our own most popular versions that they don’t trigger much of a response in the first place.
There are a couple of approaches to get around this barrier to functional chimerism. One is to start very young—i.e., to try to splice in foreign material at the genetic level, starting with the fertilized egg, so that every cell of the developing blastocyst is chimerical. This hardly ever develops into any viable organism, but at least in this case your problems are rarely immunological.
If the recipient of the graft is more developed but still fetal, the immune system is in a much earlier stage of learning friend from foe. However, the graft is still at a point of distinct disadvantage until the proteins that are distinct to the grafted tissue are caused to be represented in the protein library contained by the thymus gland. This ensures that T-cells, when they are trained, are trained to think of the grafted material’s proteins as native.
The younger the recipient is when the new proteins are introduced to the thymus, the better, of course. After puberty the thymus is largely useless and all of the T-cells in the body are trained. But success with grafted foreign tissue is already hit or miss even after the infant is a year or two old. The immune system has already learned too much.
If you want a chimeric graft to have the best chance of success, you must wipe the immune system’s slate clean and start over.
Fortunately the process for this is the same for individuals of any age.
A brand new thymus gland is in order. You will need to culture one from your recipient’s relevant pluripotent stem cells and wait for it to grow. In the meanwhile you may wish to infect your recipient with measles—or a tailored subvariant if they’ve been vaccinated—in order to clear out a large portion of antibody-producing cells that may incidentally limit the viability of your intended graft.
All of this implies a lengthy stay in a sterile environment. Your replacement thymus gland may need up to a year’s head start with the protein library already augmented if possible. Trained T-cell production won’t start until there’s a steady influx of stem cells to convert to T-cells after final implantation. Your recipient, depending on age, may also need infusions of cultured stem cells to assist in T-cell production. Oh, and a suite of childhood vaccinations to replace the knowledge of antibody manufacture lost to the measles infection.
If these interventions are successful, your recipient has a good chance of not having any untoward immunological responses to grafted material from just about any creature at all.
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Your next problems to overcome will be nutrition and maintenance. Many creatures require dietary elements that are typically missing in another creature’s diet, or at least need them in differing concentrations, so there will almost always need to be some adjustment in the diet of your chimera to meet the needs of all the tissues in play.
Using humans as a reference, we can keep in mind that many of the items humans routinely consume are poisonous to most other creatures. Human tolerance for the allium family is extraordinarily high compared to that of a cat or a dog or indeed most other mammals, though some ruminants can develop a portion of a human’s tolerance with slowly increased exposure. Hemolytic anemia and subsequent kidney damage is no joke, so it’s best to avoid garlic and onions until you’re sure they’re safe for your chimera.
Additionally the human tolerance for caffeine and other stimulants and intoxicants is also legendary in the animal kingdom. Even capsaicin can be problematic.
Many of these substances can be rendered harmless with a human digestive system, a human liver, and human excretory organs—but not all. It’s best to use caution until you’ve tested the limits of dietary tolerances. Humans are true omnivores. Procedurally it’s best to strip the diet down to that of the most limited organism and add supplements until the health of the human portion can also be maintained.
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Organic self-repair can also be an issue. Tissue repair in any creature requires a steady supply of stem cells to be put into play for healing and replacing damaged cells as well as for enabling growth or regeneration wherever it’s expected. If the grafted tissue is of significant age, it may already be somewhat depleted of stem cells and need a rejuvenating supply to be specially cultured for the tissue in question.
A long-term concern is that stem cells from both the host organism and the grafted tissue may migrate throughout the body and lodge according to unpredictable biological whim in one another. This can lead to the development of strange tissues or micro-organs or tumors with unpredictable effects. Once a stem cell is traveling in the bloodstream, anyplace where blood flows can be affected, including reproductive organs and tissues.
Ordinarily one might assume that xenografted tissue would have no effect at all on germline cells, but with migrating stem cells in mind, this is a legitimate risk. One need not worry about chimeric or hybrid offspring from affected testes as horizontal gene transfers are unlikely, but sperm samples may contain oddities and hormones produced may be atypical of either species and interfere with fertility in a general way. Ovaries may also be similarly affected up to and including the production of alternate eggs, which may become further problematic if species are involved that are capable of parthenogenesis.
One further consideration is that the presence of alien hormones and proteins can have unpredictable and undesired epigenetic effects in the host organism as well as the host organism having a similar effect on the guest tissues.
In a chimeric organism of sufficient lifespan a significant amount of unplanned hybridization—if not outright systemic corruption—can occur, all from a simple graft. This is one of the reasons that immune systems work vigorously to destroy foreign tissues in the first place.
Due to these factors, a chimeric individual will have risks of new diseases specific to the new hybrid metabolism in addition to being potentially vulnerable to illnesses and infections specific to each species involved in the hybridization.
Keep in mind that all of these concerns are strictly for biological chimerisms—at least so far. They do not apply if your intervention is strictly morphological, like creating avian-style wings from your host’s natural corporeal materials and modifying the structure to be capable of flight. They might still apply if your interventions epigenetically unlock DNA behavior from previous evolutionary adaptations that have been locked away for many millions of years, since if the proteins and hormones now being produced were not available for the thymus’s friend/foe T-cell training library since birth, many of those proteins may register as foreign.
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It’s worth noting that there is an entirely mental analog to this process that is for grafting pieces of foreign concepts and worldviews into a sapient host’s mind. The typical humanoid mind’s immune system is a good deal less complicated with respect to the physical immune system, which can be both an advantage and a drawback. The upshot is that any foreign concept will have to make it past immunological defenses before it can be accepted into the worldview of the host.
I feel like perhaps this isn’t the right place to go into that process in too much detail, but it brings us to yet another set of difficulties. The host must also mentally and behaviorally accept that the grafted material—especially if such material is visible on the surface of their body or is otherwise difficult to ignore as an addition or replacement—is a valid and accepted part of their own body. If a predator or scavenger repeatedly mistakes a limb as belonging to a food animal, for instance, they will likely injure themselves. Likewise there will be difficulty if the graft is identified as merely a foreign object—something that has grabbed on or is stuck on.
For both sapient and non-sapient creatures, this process of acclimation works better if the host is young. For an older sapient creature, the host must be capable of being convinced that the modification is part of their new physical identity.
If part of the host’s culturally indoctrinated mental immune system involves concepts of purity, now may be a good time to refer back to your notes on an earlier lecture titled “Worm at the Core.” It should be helpful to keep in mind that purity as a concept that can apply to an organism is ludicrous at the very foundation, since no organism can live without being infected by hosts of symbiotes or parasites in a running detente, and every organism must start their existence as an invasive organism in every family and every environment, seeking to establish a place of permanence, security, and acceptance.
Despite all that, if the host continues to see the graft as a defilement, there will be trouble with rejection and inevitable self-harm. And by rejection here I don’t mean any psychosomatic or immunological concern, but a conscious “I don’t want this as part of my body” rejection, complete with idle scratching and clawing and peeling and digging into their own flesh to try to remove what they feel doesn’t belong.
The psychology of consciously accepting a xenograft is akin to that of accepting a prosthesis of any kind, with the same end goal: seeing the additional material as an extension of one’s own form and including it unconsciously in one’s own self-image.
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Spiritual grafts and transplantations are far less problematic—from the perspective of the one performing the operation, that is. The substances of the sah, the intangible body, are more interchangeable, more universal, and there are fewer defensive reactions to encounters with foreign material. In fact, the term “foreign material” hardly seems to apply at all, but rather “a quantity of material with a different history” seems more accurate.
One of the implications—or proofs, depending on how you look at it—is that any nonphysical entity that consumes these substances can and will consume any of it, especially if it is poorly defended, whether by plant-like absorption or active predation.
That doesn’t mean that the history isn’t somehow retained. It has been postulated that the retained history is less of an encoded memory and more of a persistent non-local entanglement with the material with which it had previously been in contact. This “entanglement” is slow to decay under normal circumstances but can be flushed away or cut away with a number of known techniques. Until this “entanglement” is dealt with, there may be ongoing influences of an unpredictable nature in both directions.
Transplanting portions of the sah of another entity onto the sah of a human has minimal effect on the physical form of the human, especially in the short term, though the body in question may make every possible effort to grow the physical analog to the associated organ or limb or tissue to whatever limited extent it is capable.
Most human bodies are incapable of doing more than extending a few neural dendrites in the direction of where a new limb or organ would be unless they are very very young, perhaps in early stages of fetal development. Brains and portions of brains remain very malleable, however, and the analogous portions of the sah are frequently popular target sites for grafts and transplants that would affect memories and personality. It is, in fact, the chief mechanism for possession or reincarnation, as well as the mechanism by which you remember somewhat of the travels and experiences of your dreaming sah upon waking.
For an adult human, a sah-graft would mainly be noticeable as affecting the body they wear in dreams as well as being present in their conscious and unconscious self-image.
Sah-grafts are the principle mechanism by which practitioners of the occult arts direct the growth of physical protoplasmic beings, some of which have been designed for this express purpose. Some of these beings have famously learned how to perform their own grafting.
There may be a future course to cover the specifics of shapechangers, skinwalkers, and others of the protean sorts at a future date. We may even invite one of them to teach the course. But for now, let’s get back to manual interventions.
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For this lesson’s practical exercise you will be given an embryo in growth medium in the gastrula stage to which you will affix elements from a subsection of the sah-archives of the Library in an attempt to guide the growth of a minor servitor. Before you get started you will draw up a plan describing features you would like the eventual organism to exhibit and at least a sketch of the interventions and augmentations you would make to get to your goal.
The species of embryo assigned to you will be chosen at random, so please keep in mind that it may or may not have native tendencies and characteristics that could affect your designs.
My own servitor will now distribute embryos to your desks, after which you may begin.