Thanks for your review. Although this book does contain literary analysis (and quite happily so, in my opinion), this does not preclude it being a natural history; many "natural histories" are not exhaustive and offer only a survey of the major types of a form, genre, or object. The romance novel is fairly old as the (English) full-length novel form itself goes, and this long period of time, coupled with the huge 20th cent. explosion in r. novels, makes it fairly implausible for any author to in one book include all major examples of the genre. I find the author's definition of the genre to be reasonable and convincing, expecially in light of the Classical ideas of comedy and tragedy. I think most literary analysis of Du Maurier's Rebecca, for e.g., focuses rightly on the gothic and mystery elements of that novel (and from what I have read of Du Maurier's non-fiction, she would probably would not have agreed with Rebecca's being called a romance novel, anyway).
If one is of the mind that any novel with a central love story (irrespective of ending) is a romance novel, then that would broaden the genre to include much of literary, mainstream and "women's fiction." Some might say this would provide a much-needed incentive for the public to view with more respect the romance genre. But others might consider it a dilution of a genre that deserves careful analysis in its most popular and--for most loyal readers--most emotionally liberating form.