> "This illusive 20 year old ... didn’t come up with that idea of marriage on her own - it was sold to her via parents, society"

The ideas and motivations the Dr. is talking about, come primarily from evolutionary instincts.

They are innate and unconscious: people almost never have sex thinking "Hey, let's make a baby!", but their drive to have sex is a biological mechanism based on reproduction. An interesting explanation is in the book "The selfish gene" by Richard Dawkins.

Of course ideas about marriage also come from society and culture... but they are first and foremost instinctual and innate: as a matter of fact, the same drives exist among animal as well (the numbered list in the article applies to most mammals too).