Why are long term dating couples more educated than other groups?

My friends friend and her boyfriend started dating in high school and she got a PhD in biochemistry while he got an engineering degree from MIT and later another degree in law. He was the first person from his family to graduate college. I know another couple that began dating when they were 18 and she got a doctor in psychology and works as a psychologist at the local prison and he got a degree in corporate and real estate law and they are married with kids now.

Why are long term dating couples more educated than other groups?
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