Mr. Spencer further contends that natural selection, by unduly
developing specially advantageous modifications without the necessary
but complex secondary modifications, would render the constitution of a
variety "unworkable" (p. 23). But this seems hardly feasible, seeing
that natural selection must continually favour the most workable
constitutions, and will only preserve organisms in proportion as they
combine general workableness with the special modification. On the other
hand, according to Mr. Spencer himself, use-inheritance must often
disturb the balance of the constitution. Thus it tends to make the jaws
and teeth unworkable through the overcrowding and decay of the
teeth--there being, as his illustrations show, no simultaneous or
concomitant or proportional variation in relation to altered degree of
use or disuse.