FREE BOOKS

Author's List




PREV.   NEXT  
|<   27   28   29   30   31   32   33   34   35   36   37   38   39   40   41   42   43   44   45   46   47   48   49   50   51  
52   53   54   55   56   57   58   59   60   61   62   63   64   65   66   67   68   69   70   71   72   73   74   75   76   >>   >|  
a great number of species. Of all this we can know nothing: but of one thing we may feel assured, which is that the plantigrade foot is the only one that could have developed into a grasping organ; such a development being impossible to the digitigrade or the hoofed animals. One can readily see how the habit of walking on the sole might tend to a spreading of the toes, in order to obtain a wider and firmer footing. And it is equally easy to see how a free and wide motion in the great toe would aid in this result. The animal may have been at first light in weight and able to support itself on its unchanged foot, but as it increased in size and weight it would need a firmer grasp, and the final result of spreading its toes for this purpose may well have been the opposable great toe. It must be borne in mind, in this consideration, that the apes differ from the other tree-dwellers in being destitute of claws. The squirrels, the opossums, and other arboreal animals have sharp claws, by whose aid they can easily cling to the surface of the bark-covered boughs. The nails of the apes are incapable of affording them this service, and it is not easy to perceive how a foot like theirs could become adapted to locomotion in the trees otherwise than by the gaining of mobile action and grasping power in the toes. The existing habits of the ape tribe lead us to the conclusion that the ancestral animal may have soon begun to seek support from upper limbs. The plantigrade foot is one capable of readily curving into an organ of support, and in the case of the forefoot the toes would tend to spread and gain flexibility of motion, and the first toe to become opposable to the others and yield a more complete grasping power. It does not seem difficult to comprehend, from this point of view, how the feet of a five-toed plantigrade animal may in time have developed into grasping organs, since there would be required only an increased flexibility of the joints, and a wider and fuller movement of the great toes. That such a change took place in this instance the facts appear to indicate, the most simple and probable explanation of the development of the grasping power in the hands and feet of the ape being seemingly that given above. The relation of the lemurs to the apes is not clearly defined. It may be an ancestral one, or the two animals may represent distinct lines of descent. In the latter case we would have two lines of animal evol
PREV.   NEXT  
|<   27   28   29   30   31   32   33   34   35   36   37   38   39   40   41   42   43   44   45   46   47   48   49   50   51  
52   53   54   55   56   57   58   59   60   61   62   63   64   65   66   67   68   69   70   71   72   73   74   75   76   >>   >|  



Top keywords:

grasping

 

animal

 

animals

 

support

 

plantigrade

 
flexibility
 

motion

 

ancestral

 

firmer

 

increased


weight
 

result

 

opposable

 

readily

 

developed

 

development

 

spreading

 
descent
 

complete

 

habits


action

 

existing

 

conclusion

 

curving

 

forefoot

 

capable

 
difficult
 
spread
 

joints

 
defined

instance

 

simple

 

probable

 
relation
 

lemurs

 

seemingly

 

explanation

 

mobile

 
organs
 

required


change

 

represent

 

distinct

 

fuller

 

movement

 

comprehend

 
dwellers
 
equally
 

obtain

 

footing