Is an avoidance of incest/inbreeding learned or instinctive? Is the natural avoidance of incest something that is learned or is the human brain programmed by instinct to have a negative response to incest? This of course would have an evolutionary advantage and would hence make perfect sense.
This is not my field, but I gave it a quick search. This article seems to speak directly to this question, summarizing and comparing multiple theories to each other. In light of these theories, the article also seems to propose a synthesized theory of the avoidance. Formal citation below. Hope this helps!

APA Citation

Paul, R. A. (2011). Incest Avoidance: Oedipal and Preoedipal, Natural and Cultural. Journal of the American Psychoanalytic Association, 58(6), 1087–1112. https://doi.org/10.1177/0003065110395759