Core Concepts in the Science of Early Childhood Development
Brains Are Built from the Bottom Up:
Skills Beget Skills

Neural connections in different areas of the brain associated with specific functions proliferate rapidly and then begin pruning in the earliest years of life.
Brains are built in a hierarchical fashion, starting with the simplest circuits and then moving up to more complex circuits. Sensory pathways like those for basic vision and hearing are the first to develop, followed by early language skills and higher cognitive functions. Connections proliferate and prune in a prescribed order: the timing is determined genetically but experiences affect whether the circuits are strong or weak. The brain is never a blank slate – every new competency is built upon competencies that came before. Graph Source: C.A. Nelson (2000)