This is how I think the ecosystem of infection, connection and evolution works.
It's a list of facts and insights based on these facts. I compiled this a bit on the fly
so I may have forgotten something.
1) Some monsters and superhumans have the ability to see the genetic traits of an individual and determine the combatibility and the geneology. Some may be able to do both, others can do either.
2) Valravn is able to discern if MC is the son of Body or Memory just by looking at him the first time they meet, while MC is being hunted by the police.
3) Ella can see the combatibility of an individual and lure the correct monster to infect them.
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About chosens and traits:
4) The numbered are powerful beings, so finding an individual that is combatible enough to be their "heir" is a rare occurance. Chosen doesn't mean anything more than that in my opinion. They are not chosen by the numbered, they just happen to be unique most of the time.
5) I believe Ella is wrong. She thinks that it's possible for a chosen to develop traits from the other half of the pair through evolution, but it doesn't work like that. The range of abilities is determined during infection and it's up to the Superhuman, either consciously or unconsciously, to guide the powers towards something useful. If she could see what the MC sees, she would probably know it, but she lacks the experience.
6) If the individual is capable of hosting only one numbered power, they see the numbered during their evolutions.
7) If the individual is capable of hosting both powers, they see the arbiters during their evolution.
8) No matter what monster infects you, if you have combatibility with it's progenitor, you are connected to the progenitor instead. MC got infected by either Body or Memory, but speaks to the Eye. Alice got infected by Fairy but speaks to Ether.
9) If the individual is not capable of hosting a numbered power, they can still get something better than what their monster parent can do, but never reach the top. However some abilities of lower descend can be expressed in a way that are more useful than a poorly expressed numbered's power. For example, the memory reading HERO chick's power is expressed in a much better way than MC's memory reading power. MC could be better at it and he even manages to make it touchless in his third evolution, but she still has developed the better medium while MC prefers to use touch to deliver the memory power, as shown during the Mia scene.
10) However if your combatilibity is low, you need to be affected by the progenitor directly in order to get connected to it's power. This is Michael's case and it's probably a very rare occurence, but Michael managed to prove himself worthy.
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But how does infection work?
11) We've seen that depending on the monster, getting infected can be very easy to happen. Michael was infected by a radioactive ray that missed, the Leigong infected the Aldain by just zapping him, Alice got infected by just being in the proximity (not confirmed).
12) It seems to me that any attack that originates from a monster, no matter if it's physical, energy based or mental, has the potential to infect. From there on, it depends on the human's combatibility. If he isn't combatible he just ignores the infection. However the only small indication we have is Michael not getting infected by the Fairy, assuming that the infection happened touchless.
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But what is this connection during evolution?
13) Evolution is a human thing. We don't know exactly what the connection between monster parent and superhuman is, but it seems that not everyone connects to his monster parent while evolving.
14) Alexis and Clark used Xanthe's formula to evolve, and neither one of them had the usual drama of the post evolution trance. Some teeth clenching was involved and they were done. This is unlike MC, Alice and Ella's evolution. MC's evolution trances in particular are extreme. He completely loses himself for an extended period of time.
15) I think the catalyst is corruption. Xanthe's formula is sterile and HERO members use the helmet to completely nullify corruption. Non HERO superhumans don't have that choice. Klaus was extremely concerned when MC evolved because he didn't recognize the post evolution trance. Considering that he had some connection to Xanthe, it's possible that he himself never experienced it because he used Xanthe's products.
16) Ella's kids on the other are fairly familiar with the post evolution trance since they don't grow in a corruption free environemnt.
17) There is also a possibility that the connection only applies to individuals connected to very powerful monsters, like the numbered and their direct descendants.
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What if the monster parent is dead?
18) I think that the powerful monsters can't die because they operate exclusively through avatars. Any monster that can facilitate a connection during the superhuman's evolution is effectively immortal. The library says that HERO agents have claimed in the past, that the uncategorized monster, which is a corpse, has shown itself to them during their evolutions.
19) For lower level monsters who may die, I think it makes no difference, because their superhuman children can't experience the post evolution trance, nor gain the insights that higher level monsters can instill.