Biological Foundations of Adult Sexual Development Christina Parker PSY/340 Biological Psychology Instructor: Rebecca Wilson June 12, 2010 Biological Foundations of Adult Sexual Development How humans develop prenatally Humans start out as a cell that is formed from the mother’s egg and the father’s sperm. The egg and sperm carry 23 single chromosomes each and when fertilization takes place the 23 chromosomes then become paired. “All genetically normal humans, regardless of their sex, share 22 pairs of chromosomes and only one pair is different” (Wickens, 2005, p. 204). The different pair is the sex chromosomes (X and Y). A female is (X, X) and a male is (X, Y). As the cell develops into a fetus there are several hormones involved. These hormones continue to work throughout the human body as we grow from an infant into an adult. The hormones effect our sexual development and sexuality. Affects of hormones on a fetus As the fetus grows it will physically appear gender neutral, but at about 6 week gestation the Y chromosome, if present, will release a chemical called testis-determining factor which causes the internal male sex organs to start forming. If the Y chromosome is not present then this chemical is not released and the internal female sex organs will start to form. The male hormones that cause the external organs to develop are called androgens, without these we would all have female external sex organs (Spencer A. Rathus, 2005). Some of the different androgens are: testosterone, dihydrotestosterone (DHT), and Mullerian inhibiting substance (MIS). If any of these hormones are missing or do not release the amount they are suppose to at the time they are suppose to the fetus will have genetic sexual disorders such as: Klinefelter syndrome, congenital adrenal hyperplasia, pseudo-hermaphrodite, and testicular feminisation syndrome (Wickens, 2005). The lack of these hormones not only affects the physical appearance of the fetus, but also the sexual behavior as the child grows into an adult. Affects of hormones on a growing child As a child grows and hit puberty hormones come into play again. At puberty the testes and ovaries come under the control of the hypothalamus and the pituitary gland (Wickens, 2005). “To be more precise, the release of sex hormones begins with the hypothalamus, which secretes gonadotropin-releasing hormone (GnRH), which diffuses through the hypophyseal portal blood vessels to the anterior part of the pituitary” (Wickens, 2005, p. 209). Next GnRH cause the anterior pituitary to release luteinising hormone (LH) and follicle-stimulating hormone (FSH) which are then transported to the gonads. Some other hormones that come onto play are testosterone and estrogen. There are genetic conditions that cause issues during puberty as well as into adulthood. Any of the conditions that were mentioned earlier will have issues during puberty ranging from a lack of menstruation for females and a development of breast in males. Behavior can also be affected by these conditions. Behavior and the adult sexual development As the adolescent moves into adulthood these conditions can also have affects on the behavior. An excess of testosterone can cause increased aggravation. An excess of estrogen can cause an increase in feminization. Not all men behave the way society believes that they should and not all women behave the way society believes that they should. The hormone imbalances during the prenatal stage and puberty as well as some environmental effect can be determined to lead to intersexuality, bisexuality, heterosexuality, and homosexuality. Biological changes in sexual development “The prediction that sex differences must exist in the human brain comes from at least three different types of observations: men and women (or boys and girls) differ predictably in (1) behavioral traits (e. . , aggression, juvenile play); (2) average cognitive abilities; and (3) the incidence of neurological and psychiatric disorders” (In Encyclopedia of the Human Brain, 2002). “Regardless of whether these differences are due to genes, hormones, socialization, or the confluence of all three, sex differences in behavior, neuropathology, and cognitive performance must be reflected by sex differences present someplace in the nervous system” (In Encyclopedia of the Human Brain, 2002). In the human preoptic area of the hypothalamus there are four nuclei known as the interstitial nuclei of the anterior hypothalamus (INAH 1–4) (Wickens, 2005). There are differences in two of these four nuclei that are associated with sexual differences. INAH 1 and 4 are the same in both males and females. The other two are larger in males, but some homosexual males have had smaller INAH 2 and 3. While it is still controversial the differences in the human brain can either be said to cause homosexuality and other sexual identities or a result of them. While there are many differences in the human brain such as overall size, “many sex differences are likely to exist in more subtle features of the brain, such as neural connectivity or neurochemistry” (In Encyclopedia of the Human Brain, 2002). References: In Encyclopedia of the Human Brain. (2002). Retrieved June 10, 2010, from https://www. credoreference. com/entry/esthumanbrain Spencer A. Rathus, J. S. -R. (2005). Human Sexuality in a World of Diversity, sixth edition. Allyn and Bacon, Pearson Education, Inc. Wickens, A. (2005). Foundations of Biopsychology, Second Edition. Prentice-Hall.
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