RECAPITULATION 



87 



Vertebrates before him, he could not tell one from the 

 other. Progress in development, he said, was from a 

 general to a special type. In its earliest stage every 

 organism has a great number of characters in common 

 with other organisms in their earliest stages ; at each 

 successive stage the series of embryos which it resembles 

 is narrowed. The rabbit begins like a Protozoon as a 

 single cell ; after a while it may be compared to the 

 young stage of a simple vertebrate ; then to the young 

 stage of a higher vertebrate ; afterwards, to the young 

 stage of almost any mammal ; afterwards, to the young 

 stage of almost any rodent ; eventually it becomes un- 

 mistakably a young rabbit. 



Herbert Spencer expressed the same idea, by saying that 

 the progress of development is from homogeneous to 

 heterogeneous, through steps in which the individual 

 history is parallel to that of the race. But Haeckel has 

 illustrated the idea more vividly, and summed it up more 

 tersely, than any other naturalist. His " fundamental 

 biogenetic law " reads : " Ontogeny, or the development 

 of the individual, is a shortened recapitulation of phylogeny, 

 or the evolution of the race." 



It is hardly necessary to say that the young mammal is 

 never like a worm, or a fish, or a reptile. It is at most 

 like the embryonic stages of these, and it may also be 

 noticed that, as our knowledge is becoming more intimate, 

 the individual peculiarities of different embryos are be- 

 coming more evident. But this need not lead us to deny 

 the general resemblance. 



Moreover, the individual life-historv is much shortened 

 compared with that of the race. Not merely does the one 

 take place in days, while the other has progressed through 

 ages, but stages are often skipped, and short cuts are dis- 

 covered. And again, many young animals, especially those 

 " larvae " which are very unlike their parents, often exhibit 

 characters which are secondary adaptations to modes of 

 life of which their ancestors had probably no experience. 

 In short, the individual's recapitulation of racial history is 

 general, but not precise. It is seen rather in the stages 

 in the development of organs (organogenesis) than in the 

 development of the organism as a whole. 



