vary together? (_b_) What is the relation to the
social state, as more or less complex? that is to say--Do not mental
complexity and social complexity act and react on each other?

3. _Rate of mental development._--In conformity with the biological law
that the higher the organisms the longer they take to evolve, members of
the inferior human races may be expected to complete their mental
evolution sooner than members of the superior races; and we have
evidence that they do this. Travellers from many regions comment, now on
the great precocity of children among savage and semi-civilized peoples,
and now on the early arrest of their mental progress. Though we scarcely
need more proofs that this general contrast exists, there remains to be
asked the question, whether it is consistently maintained throughout all
groups of races, from the lowest to the highest--whether, say, the
Australian differs in this respect from the Hindu, as much as the Hindu
does from the European. Of secondary inquiries coming under this
sub-head may be named several. (_a_) Is this more rapid evolution and
earlier arrest always unequally shown by the two sexes; or, in other
words, are there in lower types proportional differences in rate and
degree of development, such as higher types show us? (_b_) Is there in
many cases, as there appears to be in some cases, a traceable relation
between the period of arrest and the period of puberty? (_c_) Is mental
decay early in proportion as mental evolution is rapid? (_d_) Can we in
other respects assert that where the type is low, the entire cycle of
mental changes between birth and death--ascending, uniform,
descending--comes within a shorter interval?

4. _Relative plasticity._--Is there any relation between the degree of
mental modifiability which remains in adult life, and the character of
the mental evolution in respect of mass, complexity, and rapidity? The
animal kingdom at large yields reasons for associating an inferior and
more rapidly-completed mental structure, with a relatively automatic
nature. Lowly organized creatures, guided almost entirely by reflex
actions, are in but small degrees changeable by individual experiences.
As the nervous structure complicates, its actions become less rigorously
confined within pre-established limits; and as we approach the highest
creatures, individual experiences take larger and larger shares in
moulding the conduct: there is an increasing ability to take in