Mr. Spencer infers that, because insanity is usually hereditary, and
insanity can be artificially produced by various excesses, therefore
this artificially-produced insanity must also be hereditary (p. 28).
Direct evidence of this conclusion would be better than a mere inference
which may beg the very question at issue. That the liability to insanity
commonly runs in families is no proof that strictly non-inherited
insanity will subsequently become hereditary. I think that theories
should be based on facts rather than facts on theories, especially when
those facts are to be the basis or proof of a further theory.
Mr. Spencer also points out that he finds among physicians "the belief
that nervous disorders of a less severe kind are inheritable"--a general
belief which does not necessarily include the transmission of purely
artificially-produced disorders, and so misses the point which is really
at issue. He proceeds, however, to state more definitely that "men who
have prostrated their nervous systems by prolonged overwork or in some
other way, have children more or less prone to nervousness." The
following observations will, I think, warrant at least a suspension of
judgment concerning this particular form of use-inheritance.
(1) The nervousness is seen in the _children_ at an early age, although
the nervous prostration from which it is supposed to be derived
obviously occurs in the parent at a much later period of life. This
change in time is contrary to the rule of inheritance at corresponding
periods; and, together with the unusual promptness and comparative
completeness of the inheritance, it may indicate a special injury or
deterioration of the reproductive elements rather than true inheritance.
The healthy brain of early life has failed to transmit its robust
condition. Is use-inheritance, then, only effective for evil? Does it
only transfer the newly-acquired weakness, and not the previous
long-continued vigour?
(2) Members of nervous families would be liable to suffer from nervous
prostration, and by the ordinary law of heredity alone would transmit
nervousness to their children.
(3) The shattered nerves or insanity resulting from alcoholic and other
excesses, or from overwork or trouble, are evidently signs of a grave
constitutional injury which may react upon the reproductive elements
nourished and developed in that ruined constitution. The deterioration
in parent and child may often display itself in the same organs--those
probably which are hereditarily weakest. Acquired diseases or disorders
thus appear to be transmitted, when all that was conveyed to the
offspring was the exciting cause of a lowered vitality or disordered
action, together with the ancestral liability to such diseases under
such conditions.
(4) Francis Galton says that "it is hard to find evidence of the power
of the personal structure to react upon the sexual elements, that is not
open to serious objection." Some of the cases of apparent inheritance he
regards as coincidence of effect. Thus "the fact that a drunkard will
often have imbecile children, although his offspring previous to his
taking to drink were healthy," is an "instance of simultaneous action,"
and not of true inheritance. "The alcohol pervades his tissues, and, of
course, affects the germinal matter in the sexual elements as much as it
does that in his own structural cells, which have led to an alteration
in the quality of his own nerves. Exactly the same must occur in the
case of many constitutional diseases that have been acquired by
long-continued irregular habits."[13]
INDIVIDUAL AND TRANSMISSIBLE TYPE NOT MODIFIED ALIKE BY THE DIRECT
EFFECT OF CHANGED HABITS OR CONDITIONS.
Mr. Spencer finds it hard to believe that the modifications conveyed to
offspring are not identical in tendency with the changes effected in the
parent by altered use or habit (pp. 23-25, 34). But it is perfectly
certain that the two sets of effects do not necessarily correspond. The
effect of changed habits or conditions on the individual is often very
far from coinciding with the effects on the reproductive elements or
the transmissible type. The reproductive system is "extremely
sensitive" to very slight changes, and is often powerfully affected by
circumstances which otherwise have little effect on the individual
(_Origin of Species_, p. 7). Various animals and plants become sterile
when domesticated or supplied with too much nourishment. The native
Tasmanians have already become extinct from sterility caused by greatly
changed diet and habits. If, as Mr. Spencer teaches, continued culture
and brain-work will in time produce lessened fertility or comparative
sterility, we may yet have to be careful that intellectual development
does not become a species of suicide, and that the culture of the race
does not mean its extinction--or at least the extinction of those most
susceptible of culture.
The reproductive elements are also disturbed and modified in innumerable
minor ways. Changed conditions or habits tend to produce a general
"plasticity" of type, the "indefinite variability" thus caused being
apparently irrelevant to the change, if any, in the individual.[14] A
vast number of variations of structure have certainly arisen
independently of similar parental modification as the preliminary.
Whatever first caused these "spontaneous" congenital variations affected
the reproductive elements quite differently from the individual. "When a
new peculiarity first appears we can never predict whether it will be
inherited." Many varieties of plants only keep true from shoots, and not
from seed, which is by no means acted on in the same way as the
individual plant. Seeing that such plants have _two_ reproductive
types, both constant, it is evident that these cannot both be modified
in the same way as the parent is modified. Many parental modifications
of structure and habit are certainly not conveyed to neuter ants and
bees; other modifications, which are not seen in the parents, being
conveyed instead. Many other circumstances tend to show that the
individual and the transmissible type are independent of each other so
far as modifications of parts are concerned.
It may seem natural to expect the transmission of an enlarged muscle or
a cultivated brain, but, on the other hand, why should it be
unreasonable to expect that a modification which was non-congenital in
origin should still remain non-congenital? Why should the
non-transmission of that which was not transmitted be surprising?
Mr. Spencer thinks that the non-transmission of acquired modifications
is incongruous with the great fact of atavism. But the great law of the
inheritance of that which is a development of the transmissible type
does not necessarily imply the inheritance of modifications acquired by
the individual. Because English children may inherit blue eyes and
flaxen hair from their Anglo-Saxon ancestors, it by no means follows
that an Englishman must inherit his father's sunburnt complexion or
smooth-shaven face. Of course atavism ultimately adopts many instances
of revolt against its sway. But to assume that these changes of type
_follow_ the personal change rather than cause it, is to assume the
whole question at issue. That like begets like is true as a broad
principle, but it has many exceptions, and the non-heredity of acquired
characters may be one of them.