Metcalf: Evolution and Man 
determiners results in various lighter 
shades. In the complete albino all 
pigment determiners are absent or at 
least inactive. It is altogether possible 
that specific activators must ultimately 
be brought into our conceptions of 
inheritance. 
INHERITANCE IS PARTICULAR 
The thing desirable to emphasize 
here is the particularity of inheritance. 
Every individual is a complex of minute 
discrete qualities which in inheritance 
act more or less as independent units 
and so are commonly called unit 
characters. As the independent inher- 
itance of discrete qualities was first 
discovered by Gregor Mendel, these 
unit qualities are often called Mendelian 
units, and their inheritance as inde- 
pendent characters is called Mendelian 
inheritance. It seems to many students 
to become more and more evident that 
all physical inheritance is Mendelian, 
though the phenomena are often so 
complex that their complete Mendelian 
analysis, their analysis into units of in- 
heritance, is extremely difficult or even 
completely baffling. All this is dis- 
tinctly new. 
The science of genetics is but a half 
generation old and it is still in its 
infancy. Great progress is being made, 
American biologists marching in the 
van, but the fields still unexplored are 
vast and many decades are needed for 
their conquering. 
For our present consideration the 
thing of interest is the fact that we have 
learned to some extent how to get results 
from directed breeding. We know how 
to breed out and throw away particular 
unit qualities and we know how, on the 
other hand, to collect and increase ~ 
them. Having certain unit qualities in 
a given lot of animals of any species, 
and having so analyzed them that 
we know them as units and understand 
their reaction in combination, we can 
shuffle them as we will and produce all 
sorts of combinations within the limits 
that the life processes place upon our 
experimentation. One point of much 
importance must be emphasized. While 
breeding can combine qualities already 
539 
present in the selected individuals, and 
nurture can often bring such qualities 
to fuller development, neither breeding 
nor training can put in what is not 
already present. We can make new* 
combinations, but we cannot create 
new qualities. For these we are de- 
pendent upon Nature’s gift. We must 
make the best of what she provides. 
How does this advance in our knowl- 
edge of heredity affect the future of 
man? How about eugenics? Can we 
control human development and evolu- 
tion? There are a number of subsidiary 
questions that need answering before 
we can speak confidently of the larger 
matter of human eugenics. If we 
should control marriage to this end, 
we could, of course, produce great 
physical change in man. With suffi- 
cient study probably we may come to 
understand the unit qualities in most 
if not all of his physical constitution 
and we may hope to know how these 
behave in inheritance. May we hope 
to analyze psychic qualities into units 
of inheritance? Are there such psychic 
unit qualities, and if so are they within 
reach of our analysis? Are there such 
things at all as heritable psychic quali- 
ties? At least one American psycholo- 
gist is very skeptical of the inheritance 
of psychic qualities and regards as 
especially improbable the whole idea 
of units of inheritance in psychic 
qualities. 
I know that in the field of psychology 
I “speak as a fool,” yet as a fool, I am 
convinced by the evidence that psychic 
inheritance is a fact. We don’t know 
what that which we call disposition is, 
but it seems to be a complex of psychic 
qualities, and among men and domestic 
animals it seems to be heritable. A 
Jersey bull or a Spitz dog is of uncertain 
temper. A Hereford bull or a New- 
foundland dog is more dependable. 
These qualities are heritable. Individ- 
ual dogs of the same breed differ in 
intelligence and in disposition and, 
though the evidence is as yet not care- 
fully scrutinized, we are all convinced 
that such individual differences are 
heritable. Is the savagery of the 
Apache or the mildness of the California 
