matters, is telling us very plainly that the whole question of
"heredity _or_ environment" is not a real question at all: we
are confronted in every child with a case of heredity _and_
environment, and the practical question is how to control the latter
so as to get the most from the former.

To begin, then, in a modest way to understand what is understandable,
in the faith that understanding will grow with thought and
observation, is the first duty of those who are not content to fold
their hands in resignation or despair. We know that we can control
wherever we have real knowledge. The cook knows that she cannot make
roast duck out of pork chops; but she knows also that she can make
palatable and digestible pork chops by proceeding in one way, and that
she can make tough and sickening pork chops out of the same materials
by changing her procedure. In the same way the scientific approach to
the problem of child training teaches us that, while we cannot make a
"swan out of a goose," we can make the gosling into a better goose or
a poorer goose by the treatment we apply to it.

A frequent source of doubt and misunderstanding is the universal
occurrence of such distinct types among brothers and sisters. The
query at once arises, "Have not these children the same heredity?"
Brothers and sisters have the same ancestors, but not the same
heredity. Recent biological discoveries teach us that the individual
develops from a bundle of units derived from the two parents, but the
units supplied by a parent never represent the totality of the
parents' composition, nor do all the units that are passed on come to
manifest themselves as parts of the character. The parent passes on
sample units from her or his own inheritance, so that no two
combinations are ever exactly alike. It is a commonplace observation