Several themes connect Steinbeck's interest in the drama of daily life with this database.  The literary tradition of Naturalism with its penchant for the pessimistic and the grotesque may explain why intellectual disability, epilepsy, and childhood schizophrenia are so prominent, and why characters are struck with obsessions as they battle against the fates and nature: this is where the body meets tragedy, where the fates are inherited in family history.  But Steinbeck is too sympathetic and too sharp to reduce his characters to symbols of the struggle against nature or Man's fall; he brings them to life in their courage but also their frailties, their blithe acceptance of suffering and their fight against it.

His writing likewise moves smoothly between rich, sentimental descriptions and pinched, piquant conclusions, between comic resilience and pathos; he creates dreamers and their dreams and then breaks them with a sharp snap as he slams each story shut without sentimentality.  And so, for example, Tularecito is the "little frog" who grows into a young man thinking he is a troll and searching for his home in holes in the earth ends up in "the asylum for the criminal insane at Napa" (Chapter IV).  

Physicians appear several times, including a bitter family doctor who attends the births of the Whiteside clan (Chapter XI) and the incisive, cruel doctor to Helen Van Deventer (Chapter V): they are insightful, but their compassion is frustrated by the task of fighting both nature and their patients' perseverance; they are relegated to spectators at a battle of the wills that will only leave everybody punished and dead, with them left there to pick up the pieces.