Why Do Old Couples look Alike?

Have you noticed that couples who live together for a long time tend to look alike? My grandparents really looked alike when i grew up to know them.My parents seem to be looking more alike with time.

Is it just a coincidence?     Is this true for a majority of couples?     Or you think i need to see an optician?

It's not coincidence, i guess it's the trueness of two flesh becoming one. Most old couples do look like, e.g. each time i look at the pics of Pastor Adeboye and his wife, it's like they're related cousins or a brother & sister relationship.  They so much look alike. It's lovely! It's the work of God, ma brother. ₁₊₁₌₁

though, it isn't true for all couples, but the ones that look alike are fascinating. 

It's natural. You know they've been married for so long, and the blood that moves in the system of the man is the same blood that moves in the woman due to constant sexual intercourse. So with time, you would begin to notice that they look alike.

it's because they've been copying each other's facial expressions for years and lines have formed as a result.
In psychology it's called 'mirroring.' They mirror each other's expressions subconsciously to create a sense of intimacy