The ability of the human nervous system to process information, perform complicated simultaneous mental and physical tasks, and express feelings and emotions is peerless. Because of its complexity, the human brain is the seminal achievement of biological evolution on our planet. This paper focuses on one aspect of brain complexity, neural plasticity, the ability of the nervous system to alter its output in response to changing stimuli. Several examples of neuroplasticity at the molecular, cellular, systems and cognitive levels are presented, all of which have physiological and behavioral consequences. The examples presented provide a basis for the premise that neural complexity arose from the need to perform complex functions. These examples also lend support for the notion that complex adaptive functions are subdivided into separate neural pathways which are oftentimes anatomically distinct.