Hybridogenesis, Resistance to Disease, Blood Types, Xenotransplantation . . .

[Varyon]

Originally Posted by Flyndaran

How can a species breed with another producing hybrids and not quickly disappear?

In hybridogenesis, the hybrid basically produces gametes that segregate the chromosomes based on parent. So, if mules weren't infertile and had hybridogenesis, they would essentially produce gametes that are horse gametes and donkey gametes. If mating with a horse, depending on which gamete was involved, they could produce a full-blooded horse or another mule.

If the S's do something like this (presumably with a screen that prevents the H0 gametes from going anywhere), then their "species" is a hybrid.

Originally Posted by Flyndaran

Antigens aren't junk.

As some examples for the most well known, the Rh factor structurally appears to be an ion channel of some sort, although obviously not a critical one as those without it don't suddenly up and die. Some more recent studies have indicated that the Rh factor helps against toxoplasmosis (with heterozygotes being the best off). Rh has a nasty side effect in that it can cause an Rh negative mother to kill off an Rh positive fetus. As it turns out, however, an ABO incompatibility actually blocks the mother's immune system from attacking the Rh positive fetus - while ABO incompatibility is an issue, it's nowhere near as fatal as Rh incompatibility. There are likely other functions, of course.

Originally Posted by Fred Brackin

This actually suggests randomness to me rather than unknown causal relationships i.e. Type O blood spreads in spit of making its' carrier vulnerable to malaria rather than because of it.

Oh, miscommunication rears its ugly head again. Reread that post - type O blood renders one less susceptible to malaria, not more.

[Flyndaran]

Originally Posted by vicky_molokh

Well, sorta like waterfrogs and other hybridogenetic (hybridogenic?) species. (Somehow I recalled that you were around when the original species idea was discussed, but perhaps I'm misremembering.)


Hmm. I didn't know this is atypical and that these phenomena are interlinked. Thanks for the idea.

That link does seem slightly familiar. I know that the rare fertile mules only pass on their horse chromosomes... with that one notable exception that lead to an offspring that 3/4 donkey, 1/4 horse.
I kind of re-created something similar way back with my hidden human eating cannibals. But I was only thinking in gross chromosome levels not something this complex.

Side note, we could see this as the norm for mitochondrial D.N.A. as it nearly always comes only from the mother. (Sometimes sperm mitochondria survive to add to egg's, so as usual, real world biology screws with our nice neat expectations.)

[Flyndaran]

Originally Posted by Varyon

...Rh has a nasty side effect in that it can cause an Rh negative mother to kill off an Rh positive fetus. As it turns out, however, an ABO incompatibility actually blocks the mother's immune system from attacking the Rh positive fetus - while ABO incompatibility is an issue, it's nowhere near as fatal as Rh incompatibility. There are likely other functions, of course...

My grandmother was negative, but all four of her healthy kids were positive. So it's not quite the death sentence some sites seem to suggest.

[vicky_molokh]

Originally Posted by Flyndaran

The immune system isn't just blood. I believe their are just as important tissue types that matter for transplantation. Though things aren't quite as fussy/lethal now with much more effective anti-rejection drugs.

I'm asking because I vaguely recall hearing about somebody deliberately losing native bone marrow and relying on implanting a donor's marrow later in order to produce transplant compatibility for the rest of the body. I know not to trust stuff heard on TV, so I figured it's better to ask.

Originally Posted by Flyndaran

This is all very setting technologically dependent with a near infinite number of perfectly realistic possibilities other than our present form just for humans let alone aliens.
Xenotransplant technology exists in a rather short time frame all things considered. From experimental surgeries in the 1960s to not that long in the future when possible tech makes growing organs feasible isn't that long really.

Well, surgery available to the more well-supplied biotechy characters is TL10ish. (It's mostly just the DNA-level stuff that is unavailable.) So the question is more about what is feasible in general, not by TL, and what are the plausible reasons/explanations for possibilities and impossibilities.

Originally Posted by Flyndaran

Also why would surgeons in setting even try unless one species grossly outnumbers the other(s)? Does one have strong anti-donation religions? I believe Jehovah's Witnesses with their refusal of donated blood fund artificial blood research.

Oh, this is rather complicated. It goes something like this:
The world knows the basics about S1, but that's not a very big deal biomedics-wise.
A small group knows about the existence of S2 (but not all the truth about them).
Note that the S group of species is not a product of normal evolution as we know it, but nobody in the setting knows that; so yeah, the weird stuff and the compatibility with the H0 group (and likely also with the K0 and T0 species, but that's another story) are not a coincidence and cannot be explained through quite natural means.

S2 are generally much more robust and adaptive phenotypically than both the H0 group and the S1 species. This isn't without downsides: large variation and inclination to express 'experimental' features comes with an increased number of structural defects (e.g. missing limbs or organs, misfunctioning brain sections). Yes, some of those are non-viable either directly or indirectly; the species is not as K-strategic as H0 in the early stages of their life, though they do shift back to K-strategic once a child is past the age when it's clear whether it'll be able to contribute to the society.
Anyway, I digress. The two big traits that are displayed in an overwhelming majority of S2 are their robust metabolisms (albeit not as efficient as that of one of the H0 subspecies) and their regenerative ability (albeit largely subordinate to restoring the individual's body plan, which may in fact be defective); another, much rarer trait, is a form of regeneration that essentially negates risk of dying to old age. Why yes, S2 are trivially misdiagnosed as being cancer-positive; why do you ask?

So I think by now the implications are starting to present themselves:

• Since the S-group of species is chimerism-friendly and adaptive, the idea of xenotransplants in general is something that biologists might want to investigate either way.
• Regenerative capabilities may be a path towards developing cheaper, faster growth of organs on demand.
• The mere possibility of reconfiguring and transplanting at least part of the S2 immune system is tempting. The optimism of researches can also potentially be affected by the fact that symbiotice gamete-colonies of S1 (and implicitly S2, though nobody did research on that yet) can and do manage to 'get along' with (restricted areas of) H0 organisms and provide protection against bacterial threats. (Yeah, those colonies are quite multifunctional.)

There are of course both lighter and darker possibilities along these lines.
But if done correctly, the discovery of S2 can be used for bootstrapping medical research in certain areas and providing options that are so far either scarce or unavailable.

[Flyndaran]

Originally Posted by vicky_molokh

I'm asking because I vaguely recall hearing about somebody deliberately losing native bone marrow and relying on implanting a donor's marrow later in order to produce transplant compatibility for the rest of the body. I know not to trust stuff heard on TV, so I figured it's better to ask.
...

The only way I know of removing all bone marrow functionality is with a royal butt-load of radiation. It's hard to imagine anyone in need of a transplant organ surviving that let alone benefiting.
Sounds very House like with its propensity to kill or cure plots.

[johndallman]

Originally Posted by Flyndaran

The only way I know of removing all bone marrow functionality is with a royal butt-load of radiation. It's hard to imagine anyone in need of a transplant organ surviving that let alone benefiting.

It can be done somewhat more gently with the right chemicals. There is a treatment for multiple sclerosis that starts with destroying the patient's immune system.

[Bruno]

The state of the art, when my mother had it done 6 years ago for non-Hodgekins large B-Cell lymphoma, was monoclonal antibodies specific to B-Cells. Which is very GURPS Biotech. The one of the drugs is rituximab, it's used in combination with "CHOP" therapy (A combo of drugs).

For chemotherapy, this kind of thing is applied in "heroic doses", aka freeking titanic quantities, such that the bone marrow is destroyed faster than the body can do anything about it.

For treatment of autoimmune disorders like crippling rheumatic arthritis, it's applied in theraputic doses which are carefully balanced to merely keep the bonemarrow "wounded", rather than dead.

[Anthony]

I would somewhat question whether S1 is actually a species at all, since they seem to be all hybrids. Assuming you have fertile hybrids, under normal conditions you would expect the hybrid breeding with a pure strain to produce a hybrid 50% and a pure strain 50%.

You could in principle have something about S1 hybrids which meant that (a) they only produce S1 sperm/eggs, and (b) S1 x S1 is spontaneously aborted. That means S1 hybrids could only breed with H0, and all children would be S1. You could also have a sex-linked option; if the S1 mutation is linked to the Y chromosome than all S1 hybrids will be male, and all male children will be S1 hybrids.

[Fred Brackin]

Originally Posted by Flyndaran

Type O blood lacks the A and B antigens "greasing" the blood, so malaria can't easily grab onto it. Like how that gene for resistance to H.I.V. is really also a "broken" antigen gene.

Alas, I had forgotten that Type O was the lack of such an antigen until about 5 minutes after I had shut down my computer.

In my defense the singular "the antigen" had been used without clarifying if it was the A or B antigen or even both.

Some of the logic of my post stands though. A and B antigens remain in the gene pool and even have automatic dominance without any current vital function. So they're "leftovers exploited by disease organisms" instead of "junk" but they certainly aren't part of any intelligent design. that's pretty close to random.

To re-phrase for answer that part of the OP's question, blood types do not have known functions that decisively influence hereditability enough to do more than modestly tilt their appearance in known human populations. If species S1 and S2 are derived from H0 and important uses for blood type antigens not known to us do not appear then S1 and s2 probably have a roughly similar of blood types to H0.

[vicky_molokh]

Originally Posted by Anthony

I would somewhat question whether S1 is actually a species at all, since they seem to be all hybrids. Assuming you have fertile hybrids, under normal conditions you would expect the hybrid breeding with a pure strain to produce a hybrid 50% and a pure strain 50%.

You could in principle have something about S1 hybrids which meant that (a) they only produce S1 sperm/eggs, and (b) S1 x S1 is spontaneously aborted. That means S1 hybrids could only breed with H0, and all children would be S1. You could also have a sex-linked option; if the S1 mutation is linked to the Y chromosome than all S1 hybrids will be male, and all male children will be S1 hybrids.

What part of the definition of a species does it fail to satisfy? If it's not a species, then what do you call it?

After all, it is genetically* quite distinct from both H0 and the obscure S2. It has a method of reproduction that perpetuates its genotype. There are no natural pure S1 because despite superficial sexual dimorphism, S1 are incapable of gestation (now, Exowombs solve that problem in a way). They're sort of like the Corbicula androgenetic species of molluscs, except that instead of purging the H0 genepool soon after fertilisation, they combine the pools after fertilisation, but like waterfrogs, their gametes do not inherit the H0 part of the gene pool. Thus, the offspring has a combined genotype of H0 and a hemiclonal S1, but grand-offspring will lack the H0 bits and need to mate with another H0.

(Oh, there's also horizontal S1 and S2 gene transfer involved, but that's another matter that may or may not be relevant to whether they should be classified as a species or not and why.)

* == For whatever genetic mechanism that is applicable to the setting's biology - not necessarily DNA, but whatever is a close analogue.