In real life the Librarian is based on Halsey, she is a copy of the Halsey character and the character is, in a sense, parasitic on the Halsey character. She is not an absolute copy but you can see that the L character is based on or derives from the H character. They share the mad scientist vibe, the eugenic masterplan, and the kidnap and abuse of children (H: Spartan candidates, L: bornstellar - both stolen from the safety of their families, both used to further the character's goals)

In the haloverse she predates Halsey, Halsey appears to a lesser copy of the Librarian. Halsey's work could be seen as parasitic on the Librarians work. Halsey's genetic markers, used to select her Spartan candidates may be artifacts or signs of of the Librarian's work. H is almost an L wannabe.

I've been thinking about the practicalities of L's genetic manipulations of humans.

What she is supposed to have done seems implausible but I couldn't say that it was completely impossible. If we lived in the haloverse and if L had modified human genetics... would we be able to detect her handiwork? After all, the genetic code is there for anyone to read.

I suspect that we would have noticed something by now and I think that in the five hundred years or so that would follow, by the time of Halsey's work... I think that someone would have noticed.

Given that Halsey is an oober genius and interested in genetics and the genetic potential of her Spartan supermen... I think that if anyone was to spot L's work it would be Halsey.

We saw that H knew of L (in SpOps). How much does H know about L? Does she know that L is a Lifeshaper? (probably) Has she spotted signs of L's tampering in the human genome and noticed it's presence in Spartans in particular?

What would H's opinion be of L's handiwork?

Does she know of the Mantle? Does she want it? Does she approve of the concept? Agree with it?

H seems to have had an epiphany. In Nylund's work she seems to have distanced herself from the idea that the means justify the ends. She has lost some of her mad scientist edge. But where does this put her with respect to the Librarian?

L doesn't seem to have kidnapped anybody recently. Her genetic tinkering seems to be a done deal. It happened 100,000 years ago. And H does seem to favor humanity (she is, at least, a big fan ). Does she favor humanity above all? If so, to what degree? Would H just adopt L's point of view? Do L's plans threaten H's Spartans? (Yes the Chief is in danger when he fights the Didact but it's not as if he would be safe sitting on a beach somewhere.)

Where do you think the story is going to go WRT H and L?