Sexual Dimorphism
Reproductive behaviors such as
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Reproductive behaviors such as courting, mating, and parental behavior ensure a species' survival. Although in animals these activities tend to be either distinctively male or female, humans are generally much more flexible; their high intelligence results in a much more complicated social interaction. Human sexual behavior may, however, be characterized according to the preferred partner's gender. Recent research indicates that sexual orientation may be associated with certain neuroanatomic features. The sexual dimorphic nucleus (SDN) has been found to be larger in heterosexual males and smaller among both females and homosexual men. Moreover, this observation correlates well with certain data obtained from animal studies. Sexual dimorphism may be defined as characteristic differences between males and females. In animals, some of the most sexually dimorphic behaviors include those associated with reproduction. For example, male sexual behavior involves intromission, pelvic thrusting, and ejaculation. Intromission may be defined as "entry of the penis into the female's vagina" (2:299). This act is typically followed by a rhythmic movement of the male's hips. Eventually, the process results in the discharge of semen. In contrast--at least among animals--female sexual behavior is much more passive. In many species, female reproductive behavior may merely consist of genital exposure, or lordosis. Some female animals, however, may also
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n of human brain autopsies subsequently revealed that the SDN is approximately 2.5 times larger in men than in women (3:52).
Researchers eventually focused on SDN development. It was found that the nucleus' growth depended on testosterone levels. In rats, this "androgenization" (i.e., masculinization) occurred from 4 days before birth to five days after birth. Moreover, the researchers discovered that male rat pups castrated at birth developed smaller SDNs and displayed fewer male sexual behaviors (i.e., mounting). Conversely, it was also observed that the administration of testosterone injections to female pups enlarged their SDN and caused them to exhibit masculine sexual behaviors (1:51). Besides male sex hormone, yet another factor which proved to influence SDN size was prenatal stress. Anderson et al. (1986) notes that such stress reduced the nucleus' size in male rats. Various additional articles associating the SDN with sexual behavior include the following: Anderson et al. (1986) also relates SDN size to the individual animal's level of sexual activity and De Jonge et al. (1989) observed that SDN lesions decrease male sexual behaviors (2:318). Obviously, the exact role of the SDN in male sexual behavior remains
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Some common words found in the essay are:
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Approximate Word count = 1487
Approximate Pages = 6 (250 words per page)
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Reproductive behaviors such as
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