NATURAL SELECTION 121 



of the difficulty. Evolutionists have not always been so success- 

 ful in showing how a species is able to stave off an imminent 

 peril and obtain a respite during which a lucky variation may 

 appear to save it. But now Professor Mark Baldwin 1 and 

 Professor Lloyd Morgan 2 have independently arrived at a 

 theory that makes matters much easier. " Though there is 

 no transmission of modifications due to individual plasticity," 

 writes the latter, "yet these modifications afford the conditions 

 under which variations* of like nature are afforded an opportunity 

 of occurring and of making themselves felt in race progress." 



The significance of this principle is clearly seen when it is 

 studied in connection with the family system that prevails among 

 the higher classes of animals, which feed and tend their young 

 and to some extent educate them. Among social species it rises 

 to still greater importance. In the light of this new principle 

 the tending of the young by their parents is not merely a system 

 by which waste is prevented ; it is also a system which prevents 

 a species from deviating widely from the line of development 

 that it has begun to follow. 



I shall now try to make clear, mainly by examples, how the 

 principle works. And first I shall try to show its operation 

 when parental affection is not present to bring out its further 

 possibilities. It may be stated thus : a congenital variation, in itself 

 too minute to affect the question of survival, may gain selection-value 

 through exercise. The variation having thus been saved by exercise, 

 further variations in the same direction may occur. 



The ancestors of the amphibians lived throughout their lives 

 in water, breathing the oxygen dissolved in it by means of gills. 

 Now individuals in whom a rudimentary lung appeared, a pouch 

 opening from the oesophagus, might develop the breathing 

 capacity of this rudiment by coming frequently to the surface 

 and inhaling air, or by getting out on to the bank either to rest 

 or to escape from enemies. Then there might arise a terrible 

 emergency such as comes to many " water breathers," if they 

 live in fresh-water pools ; there might be a drought causing the 



1 American Naturalist, June and July 1896. 2 Habit and Instinct, p. 315. 



3 Italics mine. 



