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.