19.6 HERBERT SPENCER

compounded, there is produced a geometric progres-
sion of changes increasing with immense rapidity.
All through the ages living creatures have as it were
been passing over a series of anvils on which the
hammers of external forces play, with tunes of ever-
increasing complexity.

(2) Internal Factors.—Passing to internal factors,
Spencer started from the fact that organic matter is
built up of very unstable complex molecules. " But a
substance which is beyond all others changeable by
the actions and reactions of the forces liberated from
instant to instant within its own mass, must be a
substance which is beyond all others changeable by
the forces acting on it from without." In any aggregate
" the relations of outside and inside, and of comparative
nearness to neighbouring sources of influences, imply
the reception of influences that are unlike in quantity,
or quality, or both; and it follows that unlike
changes will be produced in the parts thus dissimilarly
acted on/' Thus arise differentiations of structure, a
transition from a uniform to a multiform state, a
passage from homogeneity to heterogeneity, and this
must go on cumulatively. For " the more strongly
contrasted the parts of an aggregate become, the
more different must be their reactions on incident
forces, and the more unlike must be the secondary
effects which these initiate. This multiplication of
effects conspires, with the instability of the homo-
geneous, to work an increasing multiformity of
structure in an organism." Thus, if the head of a
bison becomes much heavier, what a multiplication
of effects—mechanical and physiological—must ensue
on muscles and bones and blood-vessels. Onelexity in the incidence of