BRAIN MECHANISMS AND LEARNING 



rather amusing. Upon fniding out wc did not catch our horses and cattle 

 in England with the lazo, they cried out, 'Ah, then, you use nothing but 

 the bolas.' The idea of an enclosed country was quite new to them. The 

 Captain at last said he had one question to ask me. I trembled to think how 

 deeply scientific it might be. It was 'whether the ladies of Buenos Ayres 

 were not the handsomest in the world'. I replied like a renegade, 'Charm- 

 ingly so.' He added, 'Do ladies in the other part of the world wear such 

 large combs?' I solemnly assured him that they did not. 



'They were absolutely delighted. The Captain exclaimed, 'Look there! 

 A man who has seen half the world says it is the case; we always thought so 

 but now we know it.' My excellent judgment in combs and beauty 

 procured me a most hospitable reception.' Darwin's remarks may have 

 expressed more than disinterested diplomacy, however, for at this time a 

 letter to his sister read: 'On shore, our chief amusement was riding about 

 and admiring the Spanish ladies. After watching one of these angels 

 gliding down the street, involimtarily we groaned, "How foolish English 

 women are. They can neither walk nor dress." And then, how ugly Miss 

 sounds after Signorita.' 



Leaving now the attractive ladies of Buenos Aires, the experiences of 

 Darwin's South American visit led gradually to his formulation of the 

 theory of evolution by natural selection, certainly one of the most out- 

 standing contributions to biology and one with many broad implications. 

 The ScaJa naturae, in which living beings were arranged in a spectrum of 

 increasing complexity, was familiar to earlier naturalists and to the bio- 

 logists of the eighteenth century, by whom its order was generally con- 

 ceived as the immutable product of divine creation. Darwin's revolu- 

 tionary conception, published a century ago, as the Origin of Species 

 (1859), proposed instead that natural selection, working on the range of 

 normal variations, led to survival of the fittest and so accounted, in a 

 materiahstic way, both for evolution and for the adaptation of existing 

 forms to their environments. 



Darwin's later writings, on the Descent of Man (1871) and the Expression 

 of Emotion in Man and A)iinials (1872), called more particular attention to 

 the phylogenetic development of the brain. In keeping with his contribu- 

 tions, and related to the interest in evolution created by them, views were 

 subsequently developed by Hughlings Jackson in neurology, by Pavlov in 

 physiology and by Freud in psychiatry, each of whom accounted for the 

 phylogenetic elaboration of the central nervous system in terms of a series 

 of superimposed levels, added successively as the evolutionary scale was 

 ascended. 



