"In the early sixties having begun to describe the physiology of cells in the adult (cat) visual cortex, David Hubel and I decided to investigate how the highly specific response properties of cortical cells emerged during postnatal development". This modest statement opens Torsten Wiesel's 1981 Nobel Lecture (nobelprize.org/nobelfoundation/publications/lectures). It belies the tidal wave of experiments on developmental brain plasticity that was initiated by their publications in 1963, continues to this day, and extends well beyond the occipital lobe to virtually all sensory areas, motor areas, and to "higher centers" involved in learning, memory, and decision making. To be sure many great experimentalists and philosophers dealt with the issue of nature versus nuture in brain development before them (see Lehrman, 1970), but Wiesel and Hubel were the first to recognize that the high resolution, single neuron analyses of visual response properties in cat cortex (Hubel and Wiesel, 1962; 1963a) provided a powerful in-road to deciphering how much of sensory feature extraction was fixed at birth and how much depended for its appearance on environment introduced visual activity.