MHC takes developmental psychology and reverses its normal etiology. Rather than positing stages that give rise to behaviors, MHC considers individual behaviors and then gives a system of classifying their complexity. The classification is hierarchical, so behaviors in higher complexity classes are necessarily constructed from combinations of less complex behaviors, and the classifications match the shape of developmental psychology as discovered by Piaget and Erikson, but the hierarchy is derived independently via a mathematical abstraction.
It’s short, but here’s the money quote/tl;dr