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    Influence of Heredity and Hormones of Human Behavior

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    Compare and contrast the influence of heredity and hormones of human behavior.

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    Briefly, heredity is our genetic make-up, it is the genes we inherited from our parents, including physical qualities e.g eye color, stature, hair color, etc., personality traits and even some behaviors e.g., how we posture ourselves, etc. that we inherited from our parents. It is like the foundation of a building with all the piping intact but none of the structure a yet been realized. Heredity is all the possibilities but nothing has been realized and actualized. Our hormones are part of that structure and are a large part of the building/realization/actualization of our lives. In other words, our genes which are inherited (heredity), dictate the possible range and levels of hormones (at least, in part) e.g aggressive tendencies like the father linked to testosterone, depression linked to serotonin levels, etc that impact who we are and how we feel and act. Hormones themselves are, at least in part, what dictates change, such as our moods, emotions, puberty, menopause, excitement, stress reaction, depression, and anxiety, which are often linked to hormones and varying levels of hormones. However, we do have some influence over our hormones, which we do not have over the genes through heredity. Is there a genetic marker for behavior traits?

    Whereas we do not have any influence over the genes that we inherited through heredity, we can, however, have some influence on our hormones because they are influencing and are being influenced by what is happening in our lives in the present, such as diet, exercise, medication, meditation, and even the mood we are in, which all effect and are affected by the different levels of hormones. That is, hormone levels change, but once heredity is set; it is set. However, some would argue that genetics is a study of trying to alter what has been set, and this is true to some extent, but we are still years away from being very effective with this.

    Now let's look at what research has to say in support of these ideas. Please see attached response, which is also presented below.

    Interestingly, hormones are often referred to as biological or inherited traits. For example, testosterone is a hormone that has been found to influence various human behaviors and moods, but is also referred to as a biological factor influencing behavior.

    Let's look at the evidence that hormones influences behaviors first:


    a. Testosterone influences aggressive behavior (see http://www.medicine.mcgill.ca/mjm/v06n01/v06p032/v06p032.pdf).

    This paper reviews the evidence supporting the role of testosterone as a biological factor affecting aggressive behaviour. Human studies have so far demonstrated a relationship between measures of testosterone in adolescent males and aggression (4) with similar results found in women (5). However, results from human studies have also been subjective (6-9) since results are based on psychological questionnaires and observation. For example, girls with a condition called congenital adrenal hyperplasia, in which androgens are secreted in large amounts, have been shown to act in a more rough-and-tumble way during childhood which was thought to correlate with aggression (10) (see http://www.medicine.mcgill.ca/mjm/v06n01/v06p032/v06p032.pdf).

    b. Serotonin and Norepinephrine impact mood and behavior

    Changes in the concentration of hormones can have profound effects on mood and behaviour in humans.

    Variation in hormone levels has been implicated in some psychiatric disorders such as depression. For example, 50-75% of patients with major depression show hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis characterized by excess secretion of cortisol (1,2). (see http://www.medicine.mcgill.ca/mjm/v06n01/v06p032/v06p032.pdf).

    c. Hormones and Aggression

    Aggressive behaviour in society is a serious social problem. Between 1998-1999, the number of violent offences in England and Wales rose by 6.3%, the majority of which was violence against the person (83%) (3). Although aggression is affected by various influences, there is evidence to suggest that certain biological factors (e.g., hormone levels) may modulate aggressive behaviour (http://www.medicine.mcgill.ca/mjm/v06n01/v06p032/v06p032.pdf).

    d. Hormones influence sexual behavior (e.g., testosterone, estrogen, progesterone, etc.)

    Example 1: (excerpt)

    For both males and females, various hormones can have "effects" on their sexual behaviors and thought. The following write-up deals with the male hormones mostly.

    Among these hormones, androgenic hormones - such as testosterone (T) and dihydrotestosterone (DHT) - are especially noted for their ability to "increase the predisposition to engage in sexual behavior." (Udry, 1988, p. 710). This increased predisposition towards sexual behavior is believed to be linked with hormonally effected changes in the patterning (frequency, intensity, and duration) of sexual thoughts (e.g., sexual interests, motivations, attitudes, and fantasies). The first section below deals with males, with its main focus on androgenic hormones' effects on sexual behaviors and thoughts (along with some mention of other hormones' effects). The second section deals with hormonal effects on females' sexual behavior and thoughts. http://members.shaw.ca/bodybuilding/Muscles/HormonalEffects.html

    Hormonal effects on male sexual behaviors and thoughts

    The view that there is a hormonal basis for sexual behaviors and thoughts is supported by "ample evidence" (Frayser, 1985, p. 12; see also Robbins, 1996), including evidence obtained from male adolescents (Udry, Billy, Morris, Groff, and Raj, 1985). Testosterone, which is an androgenic hormone, generally appears to be a dominant factor in male sexual libido and ejaculation, while erectile mechanisms can function despite abnormally low levels of T (Bancroft, 1984; Buvat, Lemaire, and Ratajczyk, 1996). http://members.shaw.ca/bodybuilding/Muscles/HormonalEffects.html

    Although it is not certain what levels of the various androgens produce maximum effects on the various aspects of sexuality, studies which provide T to hypogonadal men suggest that above a certain threshold, increased T levels have no further effects (Sherwin, 1988). Since normal adult males' androgen levels are above the threshold, adult males are poor subjects for investigating the effects of androgens on sexuality (Udry, 1988, p. 711). In this regard, adolescent males are good subjects, as early adolescents can be considered to be analogous to hypogonadal adult males, except that normal pubertal development of the adolescents will remedy their androgen deficit (p. 711). http://members.shaw.ca/bodybuilding/Muscles/HormonalEffects.html

    According to Udry, T is the "most behaviorally potent" androgen (Udry, 1990, p. 2; see also Udry, 1988, p. 713); although it is generally accepted that T's androgenic potency results from its conversion (by the 5a-reductase enzyme) to dihydrotestosterone (DHT) (Gower, 1995, p. 269; see also Norman and Litwack, 1987, p. 492; Demers, 1995, p. 28). Males with higher levels of T will generally also have higher levels of DHT. http://members.shaw.ca/bodybuilding/Muscles/HormonalEffects.html

    [There are "intracellular receptors that bind testosterone and DHT with high affinity" (Winters, 1995, p. 1053), but "it has not been possible to unequivocally determine in which tissues which steroid [T or DHT] is the primary or sole initiator" (Norman and Litwack, 1987, p. 495). Hence, there is continued debate over whether T or DHT is the effectually most potent androgen, with support for either position dependent on the biological location in question (Mitchell, 1996, personal communication).] http://members.shaw.ca/bodybuilding/Muscles/HormonalEffects.html

    Many of T's other actions depend on its metabolism, by an aromatase enzyme, to estradiol (Collaer and Hines, 1995, p. 57). Of the total circulating T (Total-T) in normal men, "less than 4% is free (not protein bound), 1% to 2% is bound to cortisol binding globulin, about 40% is loosely bound to albumin, and the remainder is bound with high affinity to the b-globulin, SHBG" (Winters, 1995, p. 1050; this report conflicts with Udry's assertion that "Nine-tenths or more of T is so bound [to SHBG]", 1990, p. 3). Although "the function of SHBG remains controversial" (Winters, 1995, p. 1050), T effects should be interpreted in conjunction with SHBG effects, and should be the opposite of SHBG effects (Udry, 1988). [Winters reports that "the finding of membrane binding sites for ABP (androgen binding protein) in the epididymis and for SHBG in testis ... suggests that these binding proteins" might be directly involved in androgen action (1995, p. 1050).] http://members.shaw.ca/bodybuilding/Muscles/HormonalEffects.html

    The T that is unbound to SHBG is commonly termed Free-Testosterone (Free-T), and is believed to be the portion of the total amount of T able to act on receptor cites (directly or via T's metabolites, such as DHT and estradiol), thereby influencing behaviors and thoughts (Nieschlag, 1979; Udry, 1988). The Free-T level has been reported to be between about 1 and 2.5 or 3 percent of Total-T's level (Winters, 1995, p. 1051; see also Schurmeyer and Nieschlag, 1984); although higher percentages have been reported (e.g., Hammond, Nisker, Jones, and Siiteri, 1980, estimated that Free-T comprises 2 to 8 percent of Total-T). There is a mixed use of the "Free-T" terminology in the literature. Some researchers make a clear distinction between "Free-T" and "bioavailable (non-SHBG bound) T" (e.g., Buvat, Lemaire, and Ratajczyk, 1996), while others do not (e.g., Udry, 1990; Christiansen and Winkler, 1992); and the term "Apparent Free Testosterone Concentration (AFTC)" also appears (e.g., Hjalmarsen, Aasebo, Aakvaag, and Jorde, 1996). The Free-T plus the albumin-bound T have been referred to as the non-SHBG-bound T (e.g., Gower, 1995, p. 337; Winters, 1995, p. 1051). http://members.shaw.ca/bodybuilding/Muscles/HormonalEffects.html

    The albumin-bound T, because of the low-affinity binding constant, is thought to be as readily available to target tissues as is Free-T, hence "bioavailable testosterone is calculated by subtracting the SHBG bound testosterone from the total testosterone level" (Winters, 1995, p. 1051). The Free-T index, which is calculated either as the Total-T / SHBG ratio, or as (Total-T)(SHBG) / (mean normal SHBG level), are ways "to correct the total testosterone value for variations in SHBG concentrations in plasma" (Winters, 1995, p. 1051). The Free-T index is believed to be a good indicator of measured Free-T; and is considered to be a better indicator of androgenicity than Total-T (Halpern, Udry, Campbell, Suchindran, and Mason, 1994, p. 221) (excerpted from http://members.shaw.ca/bodybuilding/Muscles/HormonalEffects.html, which lists the references)

    e. Hormones implication in gender identity issues

    Gender Identity Disorder: A Brief Description of the Problem (1997)

    Abstract: This essay briefly discusses the psychological consequences to individuals who, through differential gender development, do not fit the usual male - female model of gender identity. Several possible theories for the early onset and persistent nature of the disorder are also discussed (see http://webhome.idirect.com/~beech1/GENDERID.HTM).


    Heredity involves passing on genes through reproduction. Twin studies supports this idea, as twins reared apart often display the same types of behaviors (thus thought to be genetic or heredity). For example, traditional research strategies in behavioral genetics include studies of twins and adoptees, techniques designed to sort biological from environmental influences. More recently, investigators have added the search for pieces of DNA associated with particular behaviors, an approach that has been most productive to date in identifying potential locations for genes associated with major mental illnesses such as schizophrenia and bipolar disorder. Yet even here there have been no major breakthroughs, no clearly identified genes that geneticists can tie to disease. The search for genes associated with characteristics such as sexual preference and basic personality traits has been even more frustrating (http://www.cs.queensu.ca/~chen/Essays/PSYC1.html).

    Criminality and aggression have also been argued to be passed through the genes, as some people have an aggressive tendency and criminal seem to run in families (heredity or environmental - learned behavior?). This lends some support for the heredity side of the controversy, but as the next examples shows, there is also ample evidence to suggest that the causes of aggression and aggressive behavior are multifaceted. However, most would agree the aggressive tendency greatly impacts behavior (e.g, crime, violence, domestic and child abuse, assaults, etc.).

    a. Aggression as heredity (but multifaceted) (excerpt)

    The following essay gives a full coverage of how aggression impacts behavior form an multi-factor standpoint. Like most behavior, THOUGH, aggression can be explained in terms of a combination of hormones, heredity, social, cultural factors, to name a few impact behavior.

    Example 2: Viewing the Influences of Human Aggression from a Multi-Factor Standpoint
    July 21,2004 (Excerpt)

    Popular assumptions sprouting from ...

    Solution Summary

    This solution compares and contrasts the influence of heredity and hormones on human behavior. It provides an excellent overview of the research evidence that supports these differences with references included.