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The Development of Sexual Orientation (page 2)

By — Pearson Allyn Bacon Prentice Hall
Updated on May 1, 2014

The developmental progression described in stage models such as this one seems to be more accurate for males than females in that fewer women report feeling different from same-sex peers during childhood, and more report first experiencing same-sex attraction after reaching adulthood rather than during adolescence (Diamond & Savin-Williams, 2000; Ruble et al., 2006). And while stage models imply that a homosexual identity remains stable once it is achieved, recent research indicates that there may be more changes over time than a stage model would predict, with shifts in sexual orientation both toward and away from same-sex attraction and behavior (Savin-Williams & Ream, 2007).

Descriptions of different childhood characteristics of heterosexual and homosexual individuals are interesting and indicate that orientations may begin to develop early in life—but they do not explain why children have these characteristics. There is increasing evidence that sexual orientation is influenced to some extent by biological factors. One source of evidence comes from case studies of children who are sexually reassigned during early infancy, with boys raised as girls, or vice versa. Though rare, this happens because of prenatal problems in the development of sex organs or accidents during circumcision. Despite early reports that these children grew up to be well-adjusted members of their assigned gender, follow-up studies found that many reverted to their biological sex in terms of sexual orientation, described themselves as bisexual, or experienced sexual dysfunction related to gender identity (Byne, 2006; Money & Ehrhardt, 1972; Mustanski, Chivers, & Bailey, 2002). In addition, twin studies have found a genetic influence. There is a higher concordance in homosexuality in identical than in fraternal twins, with heritability estimates ranging from .14 to .76 (Bailey & Pillard, 1991; Mustanski et al., 2002). Genetics studies identified a location on the X chromosome shared more often by brothers who were both homosexual than by heterosexual brothers (Hamer, 1999).

Prenatal hormone levels also play a role. For example, there is a relationship between abnormal prenatal hormone levels and later behavior, personality characteristics, and sexual orientation. Girls exposed to higher-than-normal prenatal levels of androgens (male hormones) tend to show traits and preferences more typical of males, and males exposed to lower-than-normal-levels of androgens show more female-typical patterns and choices (Berenbaum & Snyder, 1995; Dittman et al., 1990; Meyer-Bahlburg et al., 1995; Mustanski et al., 2002). And autopsy studies have found that some areas of the brains of homosexual men are more similar to those of heterosexual women than to the brains of heterosexual men. Remember, however, that differences in brain structure could result from biological factors or from differences in experience (LeVay, 1993; Mustanski et al., 2002).

But even a strong biological or genetic influence on a behavior does not mean that the environment is unimportant. The same twin studies that found moderate-to-strong heritability estimates also found estimates of the influence of nonshared environment that ranged from .14 to .73. There is also ample evidence that reinforcement, punishment, and observational learning influence gender-related behaviors and preferences.

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