vicious and criminal men and women. They will remind us that from a
class of children that had the same teachers for many years has
emerged a group of very distinct men and women; they will remind us
that brothers and sisters with the identical "environment" turn out
to be so different.

On the other hand, those who see nothing in "heredity" will point to
the same Lincoln and ask confidently why his ancestors and his
descendants do not show the same degree of power and achievement.
They will point to the same family of brothers and sisters who had
the same "heredity" and ask why they all turned out so differently.
The black sheep proves just as much--and just as little--for one
side of the argument as it does for the other.

There are, it is true, many people who say that they "do not
believe" in either heredity or environment. Such people see the
difficulties of the disputants and reject both alternatives. They
prefer to say frankly that they do not understand the situation;
that life is too complex to be solved by puny human intellects. Or
they resort to some equally unintelligible explanation, such as
"Fate" or "Nature"--which is but another way of saying that we never
_can_ understand. On the other side stands the scientist who
refuses to shut his eyes to _any_ established facts, and
insists upon trying to understand as much as possible, though he may
never hope to understand all.

But no one is prepared to say authoritatively that either heredity
or environment is the exclusive or even the predominant factor in
determining the character of the individual. Indeed, the voice of
the scientist, which is the only authoritative voice we have in such