In the meantime, I had an interesting discussion with some writer friends about explanations in novels. One writer recently finished a unique horror novel. Should she explain the whole monster mythology and origins and rules within said novel? Hhm... We thought: maybe not. It was scarier not knowing what was really going on. It was scarier thinking the monsters might come to our town!
I do think this is related to genre. At some point explaining your horror turns it into a science fiction. For example, if scientist John Smith's virus escapes ABC lab and sickens folks with the result that they get super hairy, their teeth grow, and they crave live food, the story seems like SF--especially if Dr. Smith is seeking a cure. If suddenly people howl at the moon, on the other hand, it seems like horror.
Fantasy can also be turned into SF with too much explanation. For example, if folks in your story can float by waving a magic wand it seems like fantasy. If folks levitate by manipulating dark energy it seems like SF.
Please note when I say explain I'm not talking about info-dumping. The age of the info-dump is over. Don't do that in any genre. Info-dumping involves the author directly explaining things to the reader. Often this is done via narrative without characters. A rule of thumb I use is: no more than 250 words of exposition at a time. Info-dumping can also be attempted via characters using the dreaded "As you know, Bob..." Don't do this. Characters should not discuss things they already know.
Bottom line: each author has to decide for him/herself. To explain or not to explain?