NATURAL SELECTION 123 



the whole time that we were on our legs ! All day the stag was 

 carrying his antlers and his muscles were acquiring the strength 

 that was needed. But when the antlers in the course of many 

 generations had grown big, males that were born without specially 

 adapted muscles to carry them, would not be likely to be lords 

 of the herd. So that here too congenital variations would follow 

 in the wake of accommodations, due to exercise, in the 

 individual. 



The other examples which I take will show how parental The factor 

 affection gave a new importance to this principle. of parental 



T- T .11 -i i 1-11-11 1-1 affection 



first I will consider the process by which birds became bipeds, and train- 

 using their hind-limbs only for walking, and devoting their fore- in 

 limbs to flight. Let us assume that they first learnt to fly, by 

 flapping along the surface of water, flying with their wings and 

 paddling with their feet. When they took to living on land, not 

 only would flight, being unaided by the feet, be more difficult, 

 but they must become bipeds else their wing feathers will suffer. 

 Now walking on the hind legs is by no means an easy feat for a 

 bird till he has been specially adapted for it. What a clumsy 

 creature a penguin is on land ! How often he trips and tumbles ! 

 But power of running is often indispensable to a bird ; many 

 birds in the present day rise from the ground with difficulty, and 

 without ample space cannot rise at all, so that unless they were 

 good on their legs, they would be as helpless as a Boer without 

 his horse. Much less could the primitive bird when he emerged 

 onto the land do without speed of foot, unless like the penguins 

 he was lucky enough to have no land enemies to pursue him. 

 He must, therefore, practise and improve at running, and the 

 result might well be that a small peculiarity of structure would 

 be raised to importance ; having a slight gift for running he 

 would become through much practice an adept according to the 

 primitive avian standard. And now comes in the factor of parental 

 training, for we must imagine that having advanced so far in 

 strength, skill, and vitality as to be able to fly, he will not leave 

 his young to fend entirely for themselves. They will have the 

 path of life marked out for them by their parents. They must 

 not return to an aquatic existence, only occasionally landing for 



