The Editor: Heredity and the Mind 
and sisters for mental traits is the same 
as it is for physical traits, then we can- 
not help being struck by the remarkable 
coincidence. 
Or is it a coincidence? We have the 
measurement of a large number of 
traits; and as Pearson points out, any 
mathematician who calculates the 
chances that it 1s a mere coincidence, 
will find the odds so heavily against 
him that it is hardly conceivable that 
it is a mere coincidence. Prof. Pearson 
was obliged to conclude that it shows 
mental traits are inherited in the same 
way, and to the same degree as physical 
traits. This line of reasoning has not 
proved wholly acceptable to many 
psychologists; but none has yet been 
able to offer any other sensible explana- 
tion of the supposed coincidence. Prof. 
Pearson writes:!! 
“It has been suggested that this 
resemblance in the psychological char- 
acters is compounded of two factors, 
inheritance on the one hand and training 
and environment on the other. If so, 
you must admit that inheritance and 
environment make up the resemblance 
in the physical characters. Now these 
two sorts of resemblance being of the 
same intensity, either the environmental 
influence is the same in both.-cases or it 
is not. If it is the same, we are forced 
to the conclusion that it is insensible, 
for it cannot influence eye-color. If it 
is not the same, than it would be a most 
marvellous thing that with varying 
degrees of inheritance, some mysterious 
force always modifies the extent of 
home influence, until the resemblance 
of brothers and sisters is brought sensi- 
bly up to the same intensity! Occam’s 
razor!” will enable us at once to cut off 
such a theory. We are forced, I think 
literally forced, to the general conclusion 
that the physical and psychical charac- 
ters in man are inherited within broad 
lines in the same manner, and with the 
same intensity. The average home 
environment, the average parental in- 
fluence is in itself part of the heritage of 
the stock and not an extraneous and 
4 Biometrika, Vol. III, p. 156. 
461 
additional factor emphasizing the re- 
semblance between children from the 
same home.”’ 
A paragraph from Schuster! may” 
appropriately be added. ‘After con- 
sidering the published evidence a word 
must be said of facts which most people 
may collect for themselves. They are 
difficult to record, but are perhaps more 
convincing than any quantity of sta- 
tistics. If one knows well several mem- 
bers of a family, one is bound to see in 
them likenesses with regard to mental 
traits, both large and small, which may 
sometimes be accounted for by example 
on the one hand or unconscious imita- 
tion on the other, but are often quite 
inexplicable on any other theory than 
heredity. It is difficult to understand 
how the inheritance of mental capacity 
can be denied by those whose eyes are 
open and whose minds are open too.” 
Broadly speaking, it is of course true 
that man inherits nothing more than 
the capacity of making mental acquire- 
ments. But this general capacity is 
made up of many separate capacities, 
all of these capacities are variable, and 
the variations are inherited. Such is 
the unmistakable verdict of the evi- 
dence. 
It follows, then, that the only sure 
way to increase the amount of mental 
ability in the race is by encouraging 
parents who have ability to produce 
offspring, and by discouraging parents 
who lack ability from producing off- 
spring. In this way ‘the  level-- of 
ability—at least, potential ability— 
will inevitably rise with each generation. 
It follows, too, that attempts made by 
educators to create ability by education, 
where the inherited capacity does not 
exist, are doomed to failure. On the 
other hand, a scientific system of edu- 
cation which would ascertain what 
innate capacities the child has, and 
develop them as far as was desirable 
would probably produce a surprisingly 
effective result. 
Our conclusions as to the inheritance 
of all sorts of mental capacity are not 
2 “William of Occam’s Razor”’ is the canon of logic which declares that it is foolish to seek 
for several causes of an effect, if a single cause is adequate to account for it. 
13 Schuster, Edgar. 
Eugenics, pp. 159-160. London, 1913. 
