378 



The Journal of Heredity 



presenting very definite evidence of 

 kinship to their humble African cousins, 

 also display in the structure of their 

 bodies positive evidence of relationship 

 to the stem of the aristocratic primate 

 ])h\-lum. 



Quite apart from the striking similari- 

 ties produced by identical habits and 

 habitats, there are many structural 

 identities in the tree shrews and 

 lemuroids, not directly associated with 

 such habits, which can be inter] )retcd 



only as evidences of affinity. 

 ****** 



The stock from which man eventualh' 

 emerged played a very humble role for 

 long ages after many other mammalian 

 orders had waxed great and strong. 

 But the race is not always to the swift, 

 and the lowly group of mammals which 

 took advantage of its insignificance to 

 develop its powers evenly and very 

 gradually without sacrificing in narrow 

 specialization any of its possibiHties of 

 future achievement, eventually gave 

 birth to the dominant and most intelli- 

 gent of all living creatures. 



The tree shrews arc small, squirrel- 

 like animals which feed on "insects and 

 fruit, which they usually seek in trees, 

 but also occasionally on the ground. 

 When feeding, they often sit on their 

 haunches, holding the food, after the 

 manner of squirrels, in their fore paws."' 

 They are of "lively dis]josition and 

 great agility."^ These vivacious, large- 

 brained little inscctivores, linked by 

 manifold bonds of relationship to some 

 of the lowliest and most primitive 

 mammals, present in the structure of 

 their skull, teeth, and limbs undoubted 

 evidence of kinship, remote though 

 none the less sure, with their com- 

 patriots the Malaysian lemurs, and it 

 is singularly fortunate for us in this 

 inquiry that side by side there should 

 have been preser\X'd from the remote 

 Eocene times, and jjossibly earlier still, 

 these inscctivores, which had almost 

 Ijccome primates, and a little primitive 

 lemuroid, the spectral tarsier, which had 

 only just assumed the characters of the 

 l^rimate stock, when nature fixed their 



t\'pes and ]jrescrved them throughout 

 the ages, with relativ^ely slight change, 

 for us to study at the present day. 



Thus we are able to investigate the 

 influence of an arboreal mode of life in 

 stimulating the progressive develop- 

 ment of a primitive mammal and to 

 appreciate precisely what changes were 

 necessary to convert the lively, agile, 

 Ptilocercus-likc ancestor of the primates 

 into a real jjrimatc. 



In the forerunners of the mammalia 

 the cerebral hemisphere was predomi- 

 nantly olfactory in function, and even 

 when the true mammal emerged and all 

 the other senses received due representa- 

 tion in the neoi)allium the animal's 

 behavior was still influenced to a much 

 greater extent by smell impressions than 

 by those of the other senses. 



VALUE OF SENSE OF SMELL. 



This was due not only to the fact that 

 the sense of smell had already installed 

 its instruments in and taken firm pos- 

 session of the cerebral hemisphere long 

 before the advent in this dominant part 

 of the brain of an\- adequate representa- 

 tion of the other senses, but also, and 

 chiefly, because to a small land-grubbing 

 animal the guidance of smell impression, 

 whether in the search for food or as a 

 means of recognition of friends or 

 enemies, was much more ser\'iccable 

 than all the other senses. Thus the 

 small creature's mental life was lived 

 essentially in an atmosphere of odors, 

 and every object in the outside world 

 was judged primarily and predomi- 

 nantly by its smell. The senses of 

 touch, vision, and hearing were merely 

 auxiliary to the comi)elling influence of 

 smell. 



Once such a creature left the solid 

 earth and took to an arboreal life all 

 this was changed, for away from the 

 ground the guidance of the olfactory 

 sense lost much of its usefulness. Life 

 amidst the branches of trees limits the 

 usefulness of olfactory organs, but it is 

 favorable to the high development of 

 vision, touch, and hearing. Moreover, 

 it demands an agility and Cjuickness of 



■^ Flower and Lydt-kkc-r, "Mammals, Living and Extinct," 1X91. p. 618. 

 * W. K. Gregory, op. cit., p. 2M, and pj). 279, 280. 



