Subject: Physics and Natural Sciences
Language: English (U.S.)
Pages: 2
Part I Explain the difference between the primary sex characteristics and secondary sex characteristics and explain the biological foundation of sex-how people become female and male Part II Click on the link below and review the 60 min Special on Biological Bases of Homosexuality pt.1 & 2 and using the text, film and your respectful opinion address if homosexuality is nurture, nature or both and what could be the positive and/or negative in our society today

Sex Characteristics

Part I:

Difference between Primary and Secondary Sexual Characteristics

Primary sexual characteristics constitute the reproduction organs. The organs are body structures directly responsible for reproduction. Females have a uterus and a vagina while males have testicles and a penis. In summary, every part of an individual’s anatomy that is involved with the reproductive system is a primary sexual characteristic. Therefore, the female and male primary characteristics will also encompass the following structures: fallopian tubes, vulva, scrotum, cervix, clitoris, testicles, epididymis, and prostate glands.

Secondary sexual characteristics are caused by sexual hormones, which lead to physical differences between males and females. The features have the capacity to distinguish males from females in any living organism. The characteristics often appear when an individual reaches puberty (Henslin, 2012). Secondary characteristics include growth of pubic hair, facial hair in males, and development of breasts in women. Testosterone in males and estrogen in females are the hormones responsible for the development of secondary sexual characteristics in organisms. Other than the physical changes, there are also bound to be mental changes that result from the secretion of these hormones in the body of individuals.

Biological Foundation of Sex

           The biological foundation of sex is chromosomes. The primary sex characteristics develop in individuals when they are still in the womb, during the gestation period. During reproduction, the female egg has two X chromosomes while the male sperm has both the X and Y chromosome. The absence or presence of the Y chromosome during combination will determine the sex of a child. If the combination is XY, then the ovaries of the child will drop and become testes. The resultant sex of the child will be male. If the combination is XX, then the ovaries will remain in place and the child will be born a female.  

Part II:

           Prior to the 1970s, homosexuality was considered a mental disorder. However, psychological tests conclusively determined that there was sexuality was not determined by environmental factors. Based on the results of the test, the APA removed homosexuality from the Diagnostic and Statistical Manual of Psychological Disorders. Further research into the matter has led scientists to believe that biological factors (nature) rather than environmental factors (nurture) are the real causes of homosexuality in individuals. The following theories and experiments have provided evidence that genes and biological factors shape the sexual orientation of the individual.

           Experiments conducted in the 1990s on the brains of dead homosexual men revealed that their hypothalamus was structurally different from that of straight men. The suprachiasmatic nucleus, a structure found in the hypothalamus, was twice as large in a homosexual man as it was in a heterosexual male. Other studies found that the anterior commissure of the hypothalamus was larger in homosexual men than in heterosexual men. The findings are usually the basis for the argument that nature trumps nurture when it comes to homosexuality.

           Scientists have also found that the more genetically linked individuals are, the more likely they will exhibit straight or gay tendencies. Michael Bailey and Richard Pillard conducted tests on twins and non-related adopted brothers. They found that 52% of monozygotic twins were homosexuals, while 22% of dizygotic twins were homosexuals. Only 5% of non-related adopted brothers were found to be gay. The experiments are similar when the subjects are female (Cornuelle, 2010).

           There have also been studies that comprehensively show that having older brothers increases the chances of one being homosexual. Research indicates that every older brother raises the odds of homosexuality by nearly a third. The explanation for this phenomenon is that a woman’s body develops more antibodies for every consecutive male child she has. The changes increase the likelihood that she will give birth to a gay son (Sieczkowski, 2016).


Cornuelle, K. (2010, Nov 16). Nature vs. Nurture: The Biology of Sexuality. BU Today. Retrieved on 30/3/2016 from  

Henslin, J. (2014). Sociology: A down to earth approach. (12th Ed). Upper Saddle River, NJ: Pearson Higher Education.      

Sieczkowski, C. (2016, Feb 2). Men with older brothers more likely to be gay? Study expanding to biological origin. Huffington Post. Retrieved on 30/3/2016 from