"The Birthmark" uses the example of a newly-married couple to ask questions about the nature of love and the dynamic of marriage. Scientist Aylmer seems to love his wife in so far as he can perfect her into something entirely outside the realm of human imperfection. His wife Georgiana is so committed to her husband that she defines herself utterly through his vision of her. We find ourselves wondering what it means to love, to trust, and to commit to another person, and what consequences the extreme of any one of these might bring.
"The Birthmark" is as much about the institution of marriage as it is about science.
In "The Birthmark," Aylmer and Georgiana's marriage is merely allegorical.