I downloaded this free from Tor some years back. I was under the strong impression that it was SFF. I dipped in, didn't care for it, and set it aside. This time, I persevered, but I can't say I cared for the book much more.
I like some romance in my SFF, but this more an SFF sheen on bodice-ripping erotica. Learner is quite a good writer, if one with a very casual attitude toward punctuation. However, I couldn't generate much interest in her subject matter. There's far too much sexual detail for my taste; it's just one of those things that's more interesting to do than read about. I quickly grew tired of heavy-handed references to men's masculinity and women's beauty, and of the idea that a woman groping a man in public is seductive rather than crude. Even in the present day segments, there's some uncomfortable sexism in the views of gender roles and needs.
Learner leans too heavily on pop culture references; I was particularly irritated by coy references to Arnold Schwarzenegger, identified only as 'the Candidate' for governor. She does better in the past, though she's a little too eager to immerse us in the careful research she's clearly done.
The two marital relationships at the core of the story are too overwrought to be really credible, and just not very interesting. It's only Learner's skill as a writer that carried me to the end, but her rejection of standard comma use and the occasional clumsy prose made even that a tenuous journey.
Mostly, though, I was disappointed in the plot. Not only is there no real speculative element, the title Soul has virtually nothing to do with the plot. The element that's meant to be the thematic linchpin - a genetic predisposition to tolerate violence - is essentially just color for the romantic elements. There's a slight mystery element - why 19th century Lavinia killed her husband, but it turns out to be even more trivial than the science. The book never really comes to any conclusions about any of it.
All in all, both not to my taste, and a wasted opportunity to tell an interesting story in any genre.