602 
characters in hybridization. We can not 
but admit that the evidence of these known 
cases counts against the origin of charac- 
ters by gradual cumulative selection. 
In summarizing this part of our discus- 
sion, we can only state that at present it 
appears that far the greatest weight of 
evidence is opposed to the origin of a new 
unit character through the cumulative ac- 
tion of selection. 
Are we, then, to conclude that the prac- 
tise of breeders in continually selecting 
from the best for propagation is useless, 
and must we advise practical breeders to 
discontinue their selection? How can we do 
this in the light of the success of the sugar 
beet breeders? Have not Sea Island cot- 
ton growers increased and maintained the 
length and fineness of their staple by con- 
tinuous selection? Have not corn growers 
maintained high productiveness of different 
strains by selection? Are not the Jersey 
and the Holstein maintained at a high 
degree of efficiency by selection? Has not 
the speed of our trotting and pacing horses 
been increased and maintained at a high 
rate by the most careful selection? To one 
familiar with the history of agriculture and 
breeding these questions arise fast and are 
likely to be insistent. There can be no 
doubt that the practical breeders have 
made advances by selecting from the best 
individuals. No genetist or scientific 
breeder will deny this. It is simply the 
question of the interpretation of how the 
results were obtained that is in doubt and 
whether these results can be considered as 
permanent, new unit characters. Before 
we can thoroughly understand this subject 
it is probable that each individual case will 
require to be carefully analyzed; to deter- 
mine the nature of the advance made and 
the interpretation of the process or proc- 
esses concerned. At present we can only 
SCIENCE 
[N.S. Vou. XXXV. No. 903 
partially understand the phenomena pre- 
sented. 
It appears to me that we are dealing 
in breeding with two markedly distinct 
types of selection, based on different prin- 
ciples and arriving at different results, 
both right in principle and productive of 
equally valuable practical results, but of 
very different value, when considered from 
a strictly evolutionary standpoint. 
It would seem that such cases of im- 
provement as are illustrated by the sugar 
beet indicate that the continuous selection, 
generation after generation, of maximum 
fluctuations shown by a character, will re- 
sult in maintaining a strain at nearly the 
maximum of efficiency; and that within a 
pure race the progeny of a maximum 
variate which would probably be classed as 
a fluctuation, does not regress entirely to 
the mean of the race in the first genera- 
tion succeeding the selection, but that we 
only have a certain percentage of regres- 
sion similar to the regression determined 
by Galton. It would further seem to be 
indicated by the evidence now avail- 
able that in some cases we may even expect 
the continuously selected strain to exceed 
the ordinary maximum of the unselected 
population. In the Illinois corn experi- 
ments the maximum oil and protein con- 
tent seems clearly to have exceeded the 
ordinary maximum, and is certainly main- 
tained at a very high degree with a new 
mode and range of variation. If a new 
mutant of high protein content has been 
secured in the course of the experiments 
with a change of type it is probable that 
this high protein content will behave as a 
unit character in inheritance. Upon the 
other hand, if the results are interpreted as 
simply the maintenance by isolation of a 
strain produced by selecting fluctuations, 
there would probably be a rapid return to 
