575.1 396 
IV 
A Theory of Retrogression 
[? 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 asa 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 oecurred—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 
erand-daughter cells also remained adherent until reproduction ; and 
afterwards other variations of the lke 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 
