BRAIN MECHANISMS AND LEARNING 



At the racial dimension, or successive generations in time, there are the 

 typical character changes which come to identify a taxa — morphological, 

 physiological, chemical and, progressively, behavioural attributes that 

 have accumulatively changed, in a more or less directional manner, over 

 many generations. More important, and less universally recognized, has 

 been the evolution, not of adaptations, but of adaptability. Selection 

 pressures from an environment will prociuce evolutionary changes only 

 when the stock is malleable and can respond to the pressures. Systems must 

 be able to respond to experience and to tix it in some way if they arc to be 

 changed by it; and since heredity must supply the initial plasticity which 

 enables the system to respond adaptively to selection pressures — and there 

 is much current evidence that natural selection does not operate quite so 

 blindly as was at one time believed (e.g. Waddington, 1950, i960; 

 Gerard, 1960b) — the sharp line between Darwin and Lamarck is begin- 

 ning to blur. One can inherit not only mutated genes, but genes that are 

 more mutable, even genes that induce mutations in others. Adaptive 

 enzymes come into being only when both the genetic potentiality and 

 also the environmental substate are present. An organism not only can 

 learn, it can learn to learn. Learning set, attention level, motivation 

 intensity, past experience, present physiological state, type of stimulus 

 presentation and many other factors can influence the speed and effective- 

 ness of learning. And the contributions of heredity, of individual experi- 

 ence, and of current situation to many, if not all, of these factors have not 

 remotely been disentangled. 



It remains true, none the less, that learning to learn, accelerating adapta- 

 tion, speeding auto- and hetero- catalysis is the great invention of life 

 stuff". This is the epigcnetic mode. It allows living organisms to respond 

 ever more rapidly and adaptively to the environmental challenge; it 

 similarly enables mindful organisms to meet their environmental problems 

 with greater skill and speed; and it has brought about that accelerating 

 cultural change in civilizations which seems almost to have reached an 

 explosive point. Epigenesis was enhanced by increased gene mutability, by 

 the development of chromosomes and sex assortment, by adaptive changes 

 in individual characteristics (in themselves or as a richer array for the 

 action of simple natural selection), by the invention of a nervous system 

 and of highly differentiated or coded responses. 



Environment operates upon a system at all levels, differentially selecting 

 for survival particular genes or gene arrays, cells and cell aggregates, 

 organs and organ systems, and individuals and groups of various sizes. 

 The environment operates not so much on the finished product as on the 



