575.1 396 



IV 



A Theory of Retrogression 



IT is widely believed that the development of the individual is a 

 recapitulation of the life-history of the race. In other words, 

 it is believed that every individual begins life as a unicellular animal, 

 the germ, and then, in a very rapid indistinct fashion, represents, in 

 orderly succession, all its long line of ancestors, till in the end it 

 represents its parent. This recapitulation is not more wonderful and 

 mysterious than any other fact of biology. Imagine the primitive 

 world, in which only unicellular organisms were present. Suppose 

 that variations occurred amongst these, just as we know they occur 

 higher in the scale. Then we may well believe that such variations 

 as the following occurred — that, when one cell divided into two, the 

 resulting cells did not separate, as normally happened, but remained 

 adherent. This variation, which, like other variations, would tend 

 to be transmitted, and which, if fortunate, would tend to cause the 

 ultimate survival of the organisms which possessed it, would be the 

 first step in the evolution of the multicellular from the unicellular 

 organism. The dual animal which resulted would reproduce by each 

 of its cells dividing into two, so that there would be four single 

 cells which would separate, so as again to form unicellular organisms. 

 But each unicellular organism would, in general, inherit the peculi- 

 arities and repeat the life-histories of its grandparent cells by divid- 

 ing into two adherent cells. A race of two-celled organisms would 

 thus be established. We may fairly believe that in time a second 

 variation, which also proved fortunate, occurred, whereby the four 

 grand-daughter cells also remained adherent until reproduction ; and 

 afterwards other variations of the like nature, till an organism was 

 at length evolved which consisted of a multitude of cells adherent 

 for the common benefit. When this organism reproduced it would 

 be by one or more of its cells separating and dividing into two 

 adherent cells, these into four, and so on, till the parent organism 

 was represented. Ontogeny would thus necessarily recapitulate 

 phylogeny. This rule would still obtain when evolution proceeded 

 farther, and cells had become differentiated and specialised for the 

 performance of different functions. Every individual would still 

 begin as a single cell, the germ, and then, step by step, would repre- 

 sent ancestor after ancestor till, at last, he represented the last of 

 the race, the parent. The above view of heredity is necessary to 

 my argument, and apparently is opposed to other and more modern 



