Ever wondered why couples look alike after years of marriage

Marriage is expected to be a life long journey that usually involve two people of different backgrounds. Commonly you find even people of different tribes or race getting married. Usually the couple look completely different (when it comes to their looks) at the onset. In most cases after many years of marriage we then discover that this totally differently looking people now look so similar. Have you ever wondered why it is so?

There are various theories, some say that it's because they have lived together for long, some say it's because they have had so many sex, or as d Yoruba adage says that "bi ewe ba pe lara ose... etc" (if a leaf stays long on a soap it becomes soap).
After so much thought and observations, I concluded on a reason why this is so. Amongst other theories, the strongest I picked was that the resemblance is due to d the appearance of the "seed" of the marriage
Usually when two totally different (in terms of looks) gets married and give birth to their child, d child creates a balance/point of similarity between both spouse. U start getting confused, does this child look like the father or the mother. The presence of this offspring that look both like the father and mother have created a similarity in both parents that was initially not present at the onset. And as the marriage grows it is this similarity that becomes obvious to the populace.

I checked this theory out with so many couples that have spent at least 15 years in marriage and discovered to a large extent, that the resemblance followed that theory.

This is obviously not a scientific study because the process isn't scientific, but it can serve as a baseline for future studies for any interested person.