466 ON THE ZOOLOGICAL POSITION 



able to survive and maintain the plasticity of a generalised 

 sti'ucture and the functional adaj^tability that goes with it, in 

 virtue of the fact that they were cultivating their intellectual 

 powers rather than specialising for one particular kind of life. 

 Their nimbleness of mind and agility of action enabled them to 

 adapt themselves to a great variety of changing circumstances 

 without sacrificing the generalised structure of their limbs; so 

 that, when their opportunity came, they still had the mental and 

 bodily plasticity to take advantage of it, and acquire the dominant 

 position in the animal kingdom . The Lemurs and most Monkeys 

 sacrificed their chances of attaining such pre-eminence when they 

 adopted specialisations of structure and of habits to avert the 

 risk of extinction. Tarsms represents the phyluiii whose progress 

 Avas brought to a sudden stop in Eocene times by an over-develop- 

 ment of, and an exaggerated reliance upon, those specialisations 

 of vision and its cerebral insti'uments which were responsible for 

 the differentiation of the Tarsioidea from the Lemuroidea, and 

 gave impetus to those developments which produced the Anthro- 

 poidea from one of the Tarsioid families. But Tarsius was able 

 to escape extinction only by adopting the safe nocturnal habits 

 which also played a part in sparing the Lemuroidea. 



The evidence upon which my own views were based was 

 primarily a detailed examination of the bi'ain in the Primates, 

 the first results of which were submitted to the Linnean Society 

 on March 6, 1902*. 



In that memoir I explained how conclusively the structure of the 

 brain demonstrates (a) that the Lemuroidea differ from mannuals 

 of all other Orders in presenting cerebral features that are dis- 

 tinctive of the Primates; (b) that Tarsms has a brain A\hich, in 

 most respects, closely i-esembles, and is no better developed than, 

 that of such Lemuroids as the Galaginse ; but (c) that it reveals 

 a reduction of the olfactory areas and an exj)ansion and precocious 

 development of the visual cortex, which represent the commence- 

 ment of specialisations foreshadowing the emergence of distinc- 

 tively Simian features. 



This evidence is so precise and conclusive and its significance 

 so unmistakable that those who have attempted to exclude the 

 Lemuroidea from the Primates have perforce been driven to 

 repress all reference to the brain, the organ which above all 

 others has been i-esponsible for raising the Primates to the rank 

 expressed in their Ordinal name, and most plainly gives expression 

 to the distinctive features of the Order. For the outstanding 

 chai-acteristic of Man is the range of his intellectual abilities, and 

 of the Order to which he belongs the nature of the instrument — 

 the cerebral structure — which made possible the emergence of 

 such extensive powers of discrimination in one of its members. 



In each of the mammalian Orders there is a distinctive mode 

 of folding of the cerebral cortex that is due to the relative 



* "On the Morphology of the Brain in the Mauiuialia, with Special lleference to 

 that of the Lemurs, Recent and Extinct," Trans. Linn. Soc. of London, 2nd Series, 

 Zoology, vol. viii. p. 319. 



