"Instincts probably owe their origin and development to one or other
of two principles.
"I. The first mode of origin consists in natural selection or
survival of the fittest, continuously preserving actions, &c. &c. . .
.
"II. The second mode of origin is as follows:--By the effects of
habit in successive generations, actions which were originally
intelligent become as it were stereotyped into permanent instincts.
Just as in the lifetime of the individual adjustive actions which were
originally intelligent may by frequent repetition become automatic, so
in the lifetime of species actions originally intelligent may by
frequent repetition and heredity so write their effects on the nervous
system that the latter is prepared, even before individual experience,
to perform adjustive actions mechanically which in previous
generations were performed intelligently. This mode of origin of
instincts has been appropriately called (by Lewes--see Problems of
Life and Mind {233b}) the 'lapsing of intelligence.'" {233c}