Heredity is what sets the parents of a teenager wondering about each other.

Laurence J. Peter (1919–1990), best known for formulating the “Peter Principle,” also wrote a large body of aphorisms and satirical observations about everyday institutions—workplaces, schools, and family life. This quip belongs to that vein of domestic humor, playing on the common parental experience of confronting a teenager’s baffling or exasperating behavior and then half-jokingly attributing it to “bad heredity.” The line’s comic twist is that heredity becomes not a scientific explanation but a catalyst for marital suspicion: each parent implicitly blames the other’s genes. The remark circulated widely in quotation collections under Peter’s name in the late 20th century.

The joke hinges on reversing the usual comfort people take in heredity as an impersonal cause. When a teenager behaves unpredictably, parents may look for explanations that reduce their own responsibility—“it must be genetic.” Peter’s punchline exposes how quickly that impulse turns into interpersonal blame: heredity doesn’t just explain the child; it makes the parents “wonder about each other,” i.e., suspect the other parent’s family line is at fault. Beneath the humor is a sharper point about scapegoating and the fragility of self-image in parenting: when outcomes are messy, people prefer causal stories that protect themselves, even if those stories strain relationships.