let-7-C+tSa homozygotes, containing a total of 4X let-7-C dosage, display accelerated α'/β' to p.α/β and p.α/β to α/β transitions in mushroom body neuron identities during neurogenesis, compared to wild type. Consistent with this, adults show a decreased number of earlier born α'/&bgr' neurons, and an increased number of later born p.α/β neurons.