402 NATURAL SCIENCE [December 
since the retracement on which Reversed Selection works is 
apparently always small in amount, it never seems to occur in 
species that have been so rapidly evolved as these garden plants. 
Their reversion, therefore, seems to be invariably due to true 
atavism, there being apparently no room for Reversed Selection. 
Here, then, is a strong proof, convincing proof as it seems to me, 
that true atavism means a lapsing for good and all of the last steps 
made in the phylogeny. ; 
Two things are evident from the foregoing. First, that there is 
on the average a greater tendency towards reversion than towards 
evolution, that is, there is a greater tendency to revert towards the 
ancestry than away from it, in other words, there is a greater 
tendency to let lapse in the ontogeny the last steps made in the phylo- 
geny than to add other steps to them. Secondly, the strength of 
the tendency towards reversion is proportionate to the swiftness of 
the antecedent evolution, and, therefore, species which have been 
quickly evolved, tend to retrogress swiftly, whereas species, which 
have been slowly evolved, tend to retrogress slowly. For this 
reason it is that characters long established in the species are much 
more stable than more recent characters, for, in the former case, 
reversion, to be appreciable, must be to an extremely remote ancestor, 
whereas in the latter, reversion to a much less remote ancestor 
results in appreciable retrogression. 
Suppose now a certain character in a line of individuals has 
undergone evolution. Denote by the symbols A B C D E F, the 
evolution of the character in successive individuals of the line, A 
being the rudimentary character as it appeared in the first of the 
line who had it, F the character when it reached its highest per- 
fection. Suppose that cessation of selection occurs as regards this 
character. Then F tends to be lapsed, and, when it is lapsed, E 
reappears at the end of the ontogeny. But thereafter E also tends 
to be lapsed, and D to reappear, and so on, till, in the continued 
absence of selection, at length A reappears. But under the same 
law A tends likewise to disappear, and then the character vanishes 
utterly, and the race reverts to that ancestral condition when the 
character did not exist. In this manner I take it do useless parts 
disappear absolutely. Thus have disappeared, for instance, the 
limbs of the snake. Thus have disappeared the eyes of some cave- 
dwelling animals, and the many useless parts of parasites. Thus 
have vanished innumerable useless parts in every plant and animal. 
We are now in a position to consider the part played by 
reversion in nature. Every complex individual, as we know, varies 
in a thousand ways, great and small from its parent; but only here 
and there is a variation useful. The useful variations, in proportion 
to their usefulness, are preserved and, in succeeding generations, are 
