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Biological factors in human sexuality


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Biological factors in human sexuality

  1. 1. • Biological Factors in Human Sexuality• Journal article by John Bancroft; The Journal of Sex Research, Vol. 39, 2002 Biological factors in human sexuality. by John Bancroft In most species sexual behavior principally serves the purposes of reproduction. In humans, and in some other primates, other purposes for sexual behavior in addition to reproduction have evolved. In the human such purposes have been shaped and influenced by cultural factors, so that human sexuality has been expressed in many different ways, varying across cultures and over history. In spite of these powerful cultural influences, biological factors involved in sexual arousal and response remain fundamental to human sexual experience and need to be taken into account in our attempts to understand and explain the complexities and problems as well as the positive aspects of the human sexual condition. The relevant literature is vast and this paper makes no attempt to provide a comprehensive review; rather, it should be considered an overview of a number of key concepts relevant to understanding the role of biology and its interaction with culture in shaping human sexuality. SEXUAL DIFFERENTIATION Biological differentiation into male and female makes sexual reproduction possible. Males have two sex chromosomes, an X and a Y; females have two X chromosomes. Sexual differentiation is determined by the presence or absence of the Y chromosome. If there is no Y chromosome, development is along female lines. A specific part of the Y chromosome, the SRY (sex-determining gene region of the Y chromosome) is responsible for male differentiation (Haqq & Donahoe, 1998). This results in the differentiation of the primitive gonad into a testis rather than an ovary during early fetal development. The resulting testis produces not only testosterone but also Mullerian Inhibiting Factor (MIF) which actively suppresses any further development of those parts of the embryo which would otherwise develop into internal female reproductive organs. The testosterone stimulates development of male genitalia and reproductive organs: It also has organizing effects on the central nervous system which are not well understood but which increase the likelihood of male patterns of behavior after birth (Collaer & Hines, 1995). The SRY, or possibly other parts of the Y chromosome, may have other gender differentiating effects on the central nervous system which are not dependent on testosterone, but these have not as yet been identified. The bisexual potential of the embryo allows for selection of development along either male or female lines (Beach, 1976). In some instances, as with the gonad becoming either a testis or an ovary, or the female reproductive tract being actively suppressed during male development, there is clear differentiation. In other cases, such as the nipples of the male or the clitoris of the female, there is no biological need to suppress their development, even though they play no direct role in sexual reproduction. This undifferentiated overlap between male and female may apply to other structures or functions, such as orgasm in the female. Whereas orgasm is essential for the males contribution to reproduction, orgasm in the female has no obvious reproductive purpose. It has been argued that female orgasm has positive benefits which would justify its existence on evolutionary grounds, but it seems more likely that its benefits to women are a "biological bonus" resulting from the absence of active suppression of its development (Lloyd, 1993; Symons, 1979). The role that female orgasm plays in