Mark learns about his family background when he overhears a furious argument between his mother and his father.  Mark, who is a young child at the time, is hiding "under the porch", and can "hear them real plain".  In the argument Mark overhears, his father accuses his mother of infidelity, pointing out that Mark's eyes, which have a golden tinge, are like no one else's in his family, nor in hers.  This would indicate that Mark's father is someone else, a fact that Mark's mother emphatically affirms, shouting, "that's right...he ain't yours".  The fight between Mark's parents escalates out of control, and ends with them killing each other in their young son's presence.

Mark has grown up in an atmosphere of drunkenness and violence, and has grown "sick of (his parents) yelling and fighting all the time".  He "got whipped a lot, too", and it appears he most likely took shelter under the porch when his parents began their final brawl.  His vantage place protected him from physical involvement in the altercation, but did not shield him from the knowledge that he is both illegitimate, and the cause of his parents' argument.  Chillingly, his reaction to the experience evidences that he has developed the defense of asocial indifference to protect himself from emotional trauma as well (Chapter 7).