"In earlier societies where marriage did not exist..."
I could stop reading right there. There are essentially no known human societies, past or present, in which marriage does not exist. (Possible exceptions for a few very small societies in highly unusual situations.) Marriage is considered a human universal by anthropologists.
But a bit further on:
"This study looked at research being done on 33 nonindustrial populations (nonindustrial = pre-marriage, pre-contraception)"
You're seriously equating nonindustrial with a lack of marriage? You understand that the industrial revolution was less than 200 years ago, right? And that people have been getting married for all of recorded history?