72 AN INTRODUCTION TO SCIENCE 



raised that the world had not existed long enough to allow of 

 the origin of all living forms by evolution. But although, 

 to put it briefly, the biologist wants as much time as he can 

 get, he has not the least idea as to how much would suffice. 

 An interesting side issue has recently been raised. An 

 eminent zoologist has expressed the opinion that evolution in 

 early times and among primitive forms proceeded more 

 rapidly than it has done since. Evidence bearing upon this 

 view is likely to be sought for eagerly during the next few 

 years. At first sight it appears more likely that the change 

 in the rapidity of evolution has been in the opposite direc- 

 tion ; that as competition has become keener the extent of 

 variation has increased. Among simple and comparatively 

 uniform organisms favourable variations of very small extent 

 would give great advantage to their possessors. As speciali- 

 zation increases, a variation is of little use unless it is pro- 

 nounced. Just as, to reason from analogy, a new sign-board 

 sufficed to bring business to a tradesman two centuries ago ; 

 whereas only the boldest advertisements attract attention at 

 the present time. Again, it cannot be supposed that all the 

 surface of the globe became life-supporting at the same 

 epoch. As the earth cooled, the regions in which living 

 things could exist must have increased in area, and although, 

 on account of the rapidity of their multiplication, this exten- 

 sion of the life-carrying area may have counted for very 

 little, it must, in some degree, have delayed the crisis of 

 the struggle for existence. Uniformity of reproduction 

 would seem to be the primitive law. It might be supposed 

 that when the pendulum of variation first began to swing 

 its excursions were almost imperceptible, and that their 

 departures from zero have been steadily increasing ever 

 since. Indeed, the very tendency to vary is a favourable 

 variation in itself, which would be steadily increased by 

 natural selection, since the race with the greatest poten- 

 tiality of variation is the most likely to hold its own under 

 changed conditions of existence. On the other hand, the 



