Shaler.] 190 [June 5, 
much as sexual habits are among the most fixed of all habits, it re- 
quires some such explanation of the departure from the early 
mammalian usages in the exercise of this function. 
The comparatively smaller size of the pelvis of Europeans leads us 
to believe that natural selection may still be at work in determining 
the adjustments of the pelvis to its new relations., All the evidence 
goes to show that the extreme point of reduction of the diameters 
has been attained. When we look for other possible changes we are 
naturally led to the inquiry as to the possibility of developing a eapac- 
ity in the pubic symphysis for becoming separated in parturition. 
There seems to be a strong tendency to introduce this feature in 
the female of our species. The known mobility of this part of the 
pelvis in guinea pigs and seals, makes it seem not improbable that 
this occasional separation of the pubic bones may become a constant 
feature in the race. Though the aid it can give in parturition is 
small, the capacity for effecting this separation in the pelvic girdle 
would unquestionably make it possible to get a larger head through a 
smaller pelvic opening than we could otherwise do; unless, however, 
this weak articulation could be formed just before parturition, and 
strengthened afterwards, the disadvantage to the motor functions 
would quite counterbalance the advantage. It seems possible that 
this temporary relaxation of the symphysis pubis may, in turn, 
afford a line of partial relief from some of the serious inconveniences 
which menace the females of our race. 
The relations of the whole question of pressures in the upright 
position of man to the hygiene of the body, and to the future of the 
race, are of the utmost importance. The rapid and almost excessive. 
contraction of the pelvis shows that one sex at least has found the 
vertical attitude one of considerable danger. It seems not unlikely 
that this may furnish a potent argument against any change in our 
social system which tends to put a larger amount of labor upon 
woman. 
An attentive consideration of this whole matter will show us that 
it affords an admirable exemplification of the real limits of selection 
in the work of differentiation. As long as the body was horizontally 
disposed, selection could have but slight influence upon the pelvis; 
with the new needs of the upright position it became immediately 
the seat of intense selective action, leading to very important 
changes. ‘This alteration of attitude, it is true, may have been 
brought about with the codperation of selective action; but the 
