-and-error reactions that are actually preparatory to the
end-result become firmly attached to the main tendency, so that what
was by native constitution a loosely {113} organized instinct may
become, through the individual's experience, a closely organized
habit. If a man has occasion to build himself many homes, he comes,
after a while, to build almost as uniformly and surely as an insect.

Instincts Are Not Ancestral Habits

The theory of inheritance of acquired traits has gone by the board;
biologists no longer accept it. Such traits as an individual's tanned
skin acquired by living in the tropics, horny hands acquired by hard
labor, immunity to measles acquired by having measles, big muscular
development acquired by gymnastics, are not transmitted by heredity to
the children of the individual who acquired these traits.

Nor are acquired behavior traits transmitted by heredity. Learned
reactions are not so transmitted, knowledge is not, acquired skill is
not. Learn to cook, to typewrite, or pilot an airplane as perfectly as
possible, and your child will still have to learn all over again. You
may make your experience valuable to him by _teaching_ him, but not in
the way of heredity.

Language affords a good test of this matter. A child's parents, and
all his ancestors for many generations, may have spoken the same
language, but that does not relieve the child of the necessity of
_learning_ that language. He does not inherit the language habits of
his ancestors. He has no native tendency to say "dog", or "chien", or
"hund", on sight of this animal. Here in America we have children born
of stocks that have spoken foreign languages for many generations; but
English becomes their "native tongue" after a generation or two here,
that is to say, as soon as the child hears English from infancy.

In short, there is no likelihood whatever that any instinct {114} ever
originated out of a habit or learned reaction. If we could believe it
had so originated, that would furnish an easy explanation of the
origin of an instinct; but it is contrary to all the known facts.

Instincts Not Necessarily Useful in the Struggle for Existence

Some of the best-known instincts, such as feeding or mating--or
hunting, or flight from danger, or the hibernation of frogs--are so
essential for the survival of the individual or the propagation of the
next generation that we tend to assume that all instinctive behavior
has "survival value"