How can a eugenics program be the most preferable method to creating a demonhost?

[Erebus]

The warp is a realm that is separated from reality by a barrier, keeping denizens from interacting with each other Daemonic possession allows for a daemon from the warp to take possession of a human body as a host. It involves a ritual in which a human is sacrificed to the daemon, with ancient symbols carved into the flesh to bind the daemon to that particular host. These binds enslave a daemon to a master and force it to obey commands, allowing the mage to retain limited control over its actions.

The problem is that even though a daemon is bound to a host, it is still susceptible to the same daemon weaknesses, such as holy weapons, holy symbols, etc, etc, which allow it to be sent back to the warp. In addition, the daemonic essence eventually corrupts the body of the host, ultimately destroying it. Over time, the form becomes more daemonic, adopting features attributed to the daemons true form and making it obvious that the body is possessed. The daemon is forced to expend more energy to retain the body and prevent it from breaking down completely, cutting down on its effectiveness.

To get around this, the Esoteric order of Dagon has devised a millennia-long eugenics program. Over thousands of years, they would practice selective breeding among their members, recruiting outsiders when necessary or obtaining genetic samples through other means. The end goal would be to breed a perfect vessel with the correct genetic makeup for their God to posses. This host would have all the benefits of daemon hosts with none of the weaknesses, and be able to maintain Dagon long-term with no issues. After this child is conceived, a ritual would be performed in which Dagon would take possession of the embryo and be born in the human body into the world.

With recent advances in technology, the cult believes it can speed up the process for future possessions. The creation of the artificial womb has allowed children to be grown in batches, drastically cutting down on time and effort. Genes can be taken from a variety of parents and be mixed and matched to create a person with the correct genetic makeup. The cult has the financial means and influence to create facilities where embryos can be created all at once, with those successes being brought to term and failures being exterminated. This would allow them to create an army of daemon hosts quickly and cheaply.

I need a reason for why a millennia-long eugenics program would be a more preferable option of creating a perfect daemonhost, despite advances in reproductive technology. Why would this lead to the most successful outcome?

 

[Chasejxyz]

So I was nodding along and everything was going good until you said "Despite advances in reproductive technology" and now I am VERY confused. What is the time period/setting of this? If this is a regular pre-electricity/gunpowder-type fantasy, the height of reproductive technology will be a turkey baster. "Eugenics" or selective breeding is the only option (as we have done for tens of millions of years, starting with wolves > dogs and eventually plants). But if this is an urban fantasy (and has current tech), then there are options such as CRISPR and the like. But this tech is still relatively new. This order of evil guys screwing around with magic is probably much, much older than that, so they've been doing selective breeding this entire time because they had no other options.

Because of that, they probably have some Hot Opinions as to how their way is superior/better. Is part of the reason why they're trying to make a perfect host for their god is because they want said god to "fix"/rule the world? How do they feel about technology/modern humans in general? Using IVF or CRISPR might get them results faster, yes, but they could have sincerely held religious beliefs as to why they don't want to do that.

Also keep in mind that there's two parts to breeding: genotypes and phenotypes. One is what is literally your DNA (AGTC etc) and the other is how things are actually expressed. For example, you could have an X and a Y chromosome, but your DNA has an error somewhere else (or there were issues with your development) that makes your body unable to respond to testosterone. You would be a person with the genotype of a typical male but the phenotype (i.e. body/development) of a typical female. DNA can also be altered after a person is born, which is then passed on to children. If parent A has XY and parent B has XX, then the resultant offspring can be XY, but a nice blast of ionizing radiation can turn it into XZ, so now their offspring can have something that their grandparents could never possibly create.

Ionizing radiation can be a lot of things: it's the sun, it's uranium ore, it's even another person lying in bed with you or your granite countertops. Maybe there's some sort of magic that is actually ionizing radiation that tends to cause certain alterations of DNA that are very beneficial for daemons taking over a body. Maybe there is a parasite or virus that changes DNA so that it gives immunity (or at least resistance) to some of the deletrious effects of daemonic possession. Even diseases like cancer can alter the expression of DNA or DNA itself (AND you can transplant cancer from one person into another, so if there's some sort of magic tumor/growth that gives these effects, that's another avenue.) A lot of the stuff I just mentioned sounds a lot like how space marines are made in WH40K lmao. But what I'm talking about is just ideas I'm throwing out based on how DNA actually works in the real world.

And of course, it's entirely possible that modern genetic engineering/reproductive technology can do the stuff I've just mentioned, and do it in a way that has a better chance of success/less harm to the subject, but again, your evil cult of guys could have moral/theological problems with using these things. A lot of religious doctrine (especially extreme ones, like the kinds who would engage in a millennia-long breeding program to bring their demon god to the real world) say that mundane or even good things are actually extremely harmful (5G corona!!!!) or that bad things are actually good (drink this bleach to cure your autism).