122 PROBLEMS OF EVOLUTION 



pools to dry up. At this crisis some individuals are saved by 

 their lungs. They have so far developed their makeshift 

 pouches by exercise that they are able, though not without 

 strain and discomfort, to become exclusively air-breathers, till at 

 length rain comes or they have made their way to another pool 

 from which the water has not evaporated. If there is a succes- 

 sion of such droughts, there will be a further selection of those 

 who have serviceable lungs. Thus individuals tide over a crisis 

 by improving their natural gifts by exercise ; without such 

 Lamarckian methods, they would not be equal to the emergency. 

 At the same time there is a selection of those who can thus 

 improve themselves. When the next drought comes probably 

 further variations in the same direction have arisen, and there 

 would have been no opportunity for this, but for those modifica- 

 tions due to exercise which secured a respite for the species. 

 And thus modifications though not transmitted to the next 

 generation are the prelude to variations similar in tendency to 

 themselves. Before going further, I must say something to 

 justify the above illustration. It is probable that the lung was 

 in origin a fully-developed swim-bladder. But a fully-developed 

 swim-bladder may be only rudimentary when regarded as a lung. 

 There was need of exercise to make it serviceable and give it 

 selection-value in this capacity. I have felt justified, therefore, 

 in speaking of it for the sake of simplicity as a rudimentary lung. 

 One more instance. Imagine the Wapiti deer, or rather one of 

 his progenitors -this is the old puzzle set to Neo-Darwinians by 

 Mr Herbert Spencer developing great antlers through the 

 accumulation of congenital variations by Natural Selection. 

 What if the muscles and ligaments of the neck and of all the 

 co-operative machinery did not grow strong through favourable 

 variations during the same period ? The answer is plain 

 enough ; even without the help of Natural Selection the organ- 

 ism will be able to make shift for a time. Muscles can be 

 strengthened by use during the lifetime of the individual. How 

 much can be done in this way if we begin, say in our teens, and 

 exercise certain muscles regularly for half an hour a day ! How 

 great would be the result if we exercised them each day during 



