SEXUAL SELECTION IN MAN. 205

feeling displays itself chiefly as a horror of intercourse between
near kin/' Westermarck points out very truly that the prohibi-
tion of incest could not be founded on experience even if (as he
is himself inclined to believe) consanguineous marriages are
injurious to the offspring; incest is prevented "neither by laws,
nor by customs, nor by education, but by an instinct which under
normal circumstances makes sexual love between the nearest
kin a psychic impossibility/* There is, however, a very radical
objection to this theory. It assumes the existence of a kind of
instinct which can with diflSculty be accepted. An instinct is
fundamentally a more or less complicated series of reflexes set
in action by a definite stimulus. An innate tendency at once so
specific and so merely negative, involving at the same time de-
liberate intellectual processes, can only with a certain force be
introduced into the accepted class of instincts. It is as awkward
and artificial an instinct as would be, let us say, an instinct to
avoid eating the apples that grew in one's own orchard.^

The explanation of the abhorrence to incest is really, how-
ever, exceedingly simple. Any reader who has followed the dis-
cussion of Sexual selection in the present volume and is also
familiar with the "Analysis of the Sexual Impulse'* set forth in
the previous volume of these Studies will quickly perceive that
the normal failure of the pairing instinct to manifest itself in
the case of brothers and sisters, or of boys and girls brought up
together from infancy, is a merely negative phenomenon due to
the inevitable absence under those circumstances of the condi-
tions which evoke the pairing impulse. Courtship is the process
by which powerful sensory stimuli proceeding from a person of
the opposite sex gradually produce the physiological state of
tumescence, with its psychic concomitant of love and desire,
more or less necessary for mating to be effected. But between
those who have been brought up together from childhood all the
sensory stimuli of vision, hearing, and touch have been dulled by



* Crawley {The Mystic Rose, p. 446) has pointed out that It is not
legitimate to assume the possibility of an "instinct" of this character;
instinct has "nothing in its character but a response of function to en-
vironment.**



206 P8TCH0L0GT OF SEX.
