Secondary Sex Characteristics

characteristics that distinguish one sex from the other (except the sex glands, which are primary sex characteristics).

Examples of secondary sex characteristics in humans are whiskers, beard, and the Adam’s apple in the male and typical development of the breasts, shape of the pelvis, and greater development of fatty tissue in the female.

Secondary sex characteristics in male animals include characteristic bright plumage of birds and odor-producing glands and well-developed horns and tusks in mammals. Secondary sex characteristics have adaptive value in animals because they attract members of the opposite sex and play a role in combat.

Research on castration and transplantation of sex glands (from an individual of one sex to an individual of another) showed that the development of secondary sex characteristics in mammals, birds, amphibians, and fishes is related to the function of the sex glands. These experiments led the Soviet investigator M. M. Zavadovskii to divide secondary sex characteristics into dependent (eusexual), which develop as a result of the function of the sex glands, and independent (pseudosexual), which develop in total independence of the sex glands. Dependent secondary sex characteristics do not develop in a castrated animal. If they have developed by the time of castration, they gradually lose their functional role and sometimes disappear entirely. As a result of castration, males and females become largely alike. If, however, a sex gland is transplanted to such an “asexual” individual or the individual receives a sex hormone, the characteristic depen-dent secondary sex characteristics develop. For example, a spayed hen that received a male sex hormone developed the head features of a rooster (comb, beard, wattle), the ability to crow, and male behavior. Independent secondary sex characteristics (spurs or rooster plumage, for example) develop without the introduction of sex hormones. This was demonstrated in experiments involving removal of the sex glands: the characteristics were also found in castrated roosters.

In addition to dependent and independent characteristics there is also a group of somosexual or tissue-sexual secondary sex characteristics that are peculiar to one sex but are independent of the function of the sex glands. In case of castration, sexual differences according to these characteristics are completely preserved. This group of secondary sex characteristics is typical of insects.

M. S. MITSKEVICH