Lev Vygotsky believed that development :

Concept: Vygotsky's sociocultural theory holds that cognitive development is driven primarily by social interaction with more knowledgeable others (parents, teachers, peers), mediated by language and other cultural tools. Higher mental functions appear first on the social plane, between people, and only later become internalized within the individual. This same emphasis on guided social interaction underlies his concept of the "zone of proximal development" — the gap between what a learner can do alone and what they can do with assistance.

Application: The question asks what Vygotsky believed to be the primary source of development. Since his central claim is that interaction with others in a social and cultural context is what drives cognitive growth, the option stating that development "results directly from social interaction" matches his theory.

Cross-check — contrasting the other statements by value:

• "is discontinuous in nature" describes an account of development built around fixed, universal stages — the position associated with Piaget's stage theory, whose sequence differs from Vygotsky's socially embedded, tool-mediated account of change.

• "is an unfolding of genetic programming" describes a nativist/maturationist position in which change follows an innate genetic blueprint, which is not the mechanism Vygotsky proposed.

• "results directly from maturation" again attributes change mainly to biological growth rather than to social mediation, which is the reverse of Vygotsky's emphasis.

Result: Vygotsky's sociocultural theory therefore matches "results directly from social interaction."