Two identical seeds, cultivated under opposing conditions, would yield two different plants: one tall, robust, and fertile; the other stunted, wilted, and unproductive. The second plant is not diseased: it only lacked the conditions required to reach its full potential. Moreover, if it does develop some sort of plant ailment in the course of its life, it would be easy to see how a deprived environment contributed to its weakness and susceptibility. The same principles apply to the human brain.
