Relation of Higher Animals to Man 557 



We thus consider that the increasingly high speciahzation 

 of the anterior Hmbs for one particular and circumscribed func- 

 tion may become associated with a correspondingly high de- 

 gree of specialization in the tissues, and may also reflexly con- 

 fer alert and energetic movement for most parts of the body, 

 as well as safety in connection with the organism's ability to 

 secure food quickly and widely. But the size, complexity, 

 and weight of the brain may not advance in corresponding 

 ratio, owing to modification of the forelimbs into organs that 

 have one limited function, and which thus cause a limited and 

 uniform set of stimuli to pass to the brain, and so a limited 

 degree of reaction to be exhibited by the organism as a whole. 



The decidedly gregarious or social habits of the crow, the 

 penguin, and not a few other birds doubtless have exerted a 

 stimulating action on the brain. But until a minute compara- 

 tive study has been made of the weight of the different centers 

 of the brain in solitary as compared with gregarious species it 

 will be impossible to reach any exact conclusion. 



We have already accepted that the marsupials represent the 

 most primitive group of viviparous manunals, and that strong 

 evidence exists, alike palseontological, anatomical, and taxo- 

 nomic, for considering that several families have evolved from 

 them, of which the Carnivora, the Insectivora, the Rodentia, 

 the Lemurida, and the Anthropomorpha are directly derived 

 descendants from them. In the cretaceous and early tertiary 

 beds all of these groups are well represented, and have assumed 

 anatomic features by which they are classified. One group of 

 mammals, however, that will receive attention in this chajiter 

 is that of the Proboscidea or elephant and manmioth series. 



The evolutionary origin of the group is still very imperfectly 

 known, though several palaeontologists have furnished evidence 

 of remarkable semi-primitive forms, mainly from the eocene 

 of Egypt. Since that time to the present day the proboscis 

 has doubtless been slowly evolving, and, as we shall trj^ to 

 indicate below, on the principle of action and reaction. 



When comparison is made between the brains of the early 

 mammalian groups cited above, and their existing tribes or 



