DIRECT EQUILIBRATION 197

modification brings another in its train; there are
secondary and tertiary effects. And as the increasing
assemblage of individuals arising from a common
stock is tlras liable to lose its original uniformity and
to grow more pronounced in its multiformity, indirect
effects follow from inter-crossing and from altered
competitive conditions. Moreover, as times and
seasons and ages pass, the environment goes on
changing, and on previous complications wrought by
incident forces, new complications are continually
superimposed by new incident forces. Thus there is
an almost continuous movement towards heterogeneity.
But how is that kind of heterogeneity insured which
is required to carry on life ? How is the evolution
directed ?

(3) Direct •Equilibration,—How is it that action and
reaction between the organism and its environment
bring about effective adaptations ? Spencer's answer is
that every change is towards a balance of forces, and
can never cease until a balance of forces is reached.
** Any uuequilibrated force to which an aggregate is
subject, if not of a kind to overthrow it altogether,
must continue modifying its state until an equilibrium
is brought about." Thus " there go on in all
organisms, certain changes of function and structure
that are directly consequent on changes in the incident
forces—inner changes by which the outer changes
are balanced, and the equilibrium restored." " That
a new external action may be met by a new internal
action, it is needful that it shall either continuously
or frequently be borne by the individuals of the
species, without killing or seriously injuring them;
and shall act in such a way as to affect their functions." in the incidence of