242 A STUDY IN HEREDITY 



APPENDIX E 



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 and indistinct fashion, repre- 

 sents, 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 pre- 

 sent. 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 for- 

 tunate, 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 peculiarities and repeat the 

 life-histories of its grandparent cells by dividing 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 granddaughter cells 

 also remained adherent until reproduction, and afterwards other 

 variations of the like nature, till an organism was at length evolved 



