Somewhat similarly to an “evolutionary tree” with shared ancestors, abused people were often abused themselves. “Breaking the chain” of trauma could also be considered a “mutation”, in that its another form of nature “rolling the dice” to see what pans out. Conversely, people with happy lives often create happy children, perpetuating the behavior.
I’ve heard that people with post traumatic stress can pass it on to their children, which certainly seems to be the case in my family.