236
WILLIAM C. YOUNG
into adult males castrated at birth undergo cyclic changes, he postulated "that some neural structure in the male animal becomes differentiated and fixed in its function under the influence of androgens in early
life." The suggestion was developed further following an investigation
of the pattern of gonadotropin release in adult female and male rats
injected at 5 days of age with testosterone propionate and estradiol
benzoate, respectively (392e). Everett et al. (418), writing out of a
background of experience with the neurogenic stimulation of gonadotropin secretion, were more definite. They agreed with Pfeiffer that the
steadily secreting male-type hypophysis is determined by the action of
androgen during infancy, but expressed the belief that the sex difference
resides in the hypothalamus. Continuing, they wrote: "It appears that
in rats during infancy the action of androgen conditions differentiation of
the hypothalamic 'center as an intrinsically acyclic mechanism. However, in an intact genetic female . . . , the 'center' differentiates as an
intrinsically cyclic mechanism." As far as the control of gonadotropin
secretion is concerned, the hypothalamus undoubtedly is the structure
on which testicular hormones act during the formative period, but knowing as we do now that behavior as well as the type of gonadotropin
secretion is involved, it may be well to avoid more than the generalization given by Harris (392c,d, 416) and Harris and Levine
(392e).
X. Concluding Remarks
The presentation of comparative data leads almost inevitably from
the subject of phyletic similarities and differences to evolution. In a
survey of the relationships between the hormones and behavior the
limitations of the data are such that we are pretty much restricted to
reproductive behavior. Within this sphere the similarities outnumber
the differences. The hormones are the same—testosterone in the males,
estradiol-17/?, estrone, and progesterone in the females. Testosterone
seems essential for mating and courtship behavior and is important for
the level of aggressiveness. A peculiarity of the action of this hormone
which is encountered from fishes to man is the long persistence of its
effects following castration. Estrogens are essential for mating behavior
in all species and for nest building in the females in which this behavior
is displayed. Progesterone appears to be important for incubation and
parental behavior in birds and for mating behavior and nest building
in a number of mammals. The possibility of pituitary involvement has
been suggested for the courtship and nest-building behavior of at least
one fish (58), for the land to water migration of certain salamanders, for
the migratory and parental behavior of birds, for aggressive behavior of
one bird (232), and for parental behavior of mammals. There is evidence
WILLIAM C. YOUNG
into adult males castrated at birth undergo cyclic changes, he postulated "that some neural structure in the male animal becomes differentiated and fixed in its function under the influence of androgens in early
life." The suggestion was developed further following an investigation
of the pattern of gonadotropin release in adult female and male rats
injected at 5 days of age with testosterone propionate and estradiol
benzoate, respectively (392e). Everett et al. (418), writing out of a
background of experience with the neurogenic stimulation of gonadotropin secretion, were more definite. They agreed with Pfeiffer that the
steadily secreting male-type hypophysis is determined by the action of
androgen during infancy, but expressed the belief that the sex difference
resides in the hypothalamus. Continuing, they wrote: "It appears that
in rats during infancy the action of androgen conditions differentiation of
the hypothalamic 'center as an intrinsically acyclic mechanism. However, in an intact genetic female . . . , the 'center' differentiates as an
intrinsically cyclic mechanism." As far as the control of gonadotropin
secretion is concerned, the hypothalamus undoubtedly is the structure
on which testicular hormones act during the formative period, but knowing as we do now that behavior as well as the type of gonadotropin
secretion is involved, it may be well to avoid more than the generalization given by Harris (392c,d, 416) and Harris and Levine
(392e).
X. Concluding Remarks
The presentation of comparative data leads almost inevitably from
the subject of phyletic similarities and differences to evolution. In a
survey of the relationships between the hormones and behavior the
limitations of the data are such that we are pretty much restricted to
reproductive behavior. Within this sphere the similarities outnumber
the differences. The hormones are the same—testosterone in the males,
estradiol-17/?, estrone, and progesterone in the females. Testosterone
seems essential for mating and courtship behavior and is important for
the level of aggressiveness. A peculiarity of the action of this hormone
which is encountered from fishes to man is the long persistence of its
effects following castration. Estrogens are essential for mating behavior
in all species and for nest building in the females in which this behavior
is displayed. Progesterone appears to be important for incubation and
parental behavior in birds and for mating behavior and nest building
in a number of mammals. The possibility of pituitary involvement has
been suggested for the courtship and nest-building behavior of at least
one fish (58), for the land to water migration of certain salamanders, for
the migratory and parental behavior of birds, for aggressive behavior of
one bird (232), and for parental behavior of mammals. There is evidence