The story takes place during the reproductive years of John and Jenny’s marriage. Jenny is eager for a baby but reads the death of their houseplant as an ominous sign of her parenting skills. Jenny killing the houseplant that John gives her as a gift foreshadows the reproductive health issues ahead for the Grogans: miscarriage, neutering, performance issues, another complicated pregnancy, and postpartum depression. Successfully caring for Marley confirms for Jenny that she’s ready to be a parent. Jenny’s parenting years begin just after Marley is neutered, signifying the end of his bloodline and the beginning of John’s, and foreshadowing the shift in Marley’s role from childlike puppy to quirky uncle in the Grogan family.

Marley’s death becomes the focus of John’s reflections as Marley’s age progresses and his health declines. John knows Marley will not be with the family forever, and he’s experienced the lifecycle of a family dog as a child with Saint Shaun. Marley’s age still creeps up on John, who has thrown himself into family life just as Marley reaches adolescence. By the time the Grogans move to Pennsylvania and John slows down enough to turn his attention to Marley more frequently, it’s impossible to miss the signs of aging.