Introduction
Studies on human growth and development have identified a range of behaviors whose development is dependent on hormonal development. While human behaviour is influenced by numerous factors, hormones are specifically noted for the natural control of certain behaviors; most of which influence continuity such as the sexual behaviors. Past studies on the behavioural mechanisms of the mammalian body indicate that hormones influence behaviour both directly and indirectly (Nelson, 2005). However, the mechanisms through which the influence occurs are usually many and complicated ad as such there is still much to be studied. The hormonal control of the human behavior is usually studied under behavioural endocrinology; the study of the endocrine system. One of the major tasks of the endocrine system revolves around growth maintenance; thus has major impact in long-term human behaviour. Aggressiveness in males is a major concern regarding hormonal influences while in women, hormonal influences during the menstruation period are of particular importance to their sexual behaviors.
How Hormones are involved in Behavioural Control
First, it is imperative to do an overview of the various neurotransmitters and hormones that impact on behaviour. These substances are often categorized into neuropeptides; vasopressin and oxytocin and steroids; androgens, estrogens, glucocorticoids and progestin; proteins; and prolactins (Schlenker, et al. 1993). In influencing behavioural, these chemical substances act either as neurotransmitters, neuro-modulators and/or hormones. Hormones influence behavior by inducing certain changes within the human body, usually with the involvement of the brain. For instance, thyroid hormones do influence neural activity and hence affecting the release of hormones that impact on mood. Thus, it is as a result of modifications in certain parts of the brain that behaviour is altered through hormonal influence (Breedlove, et al. 2007). Experts argue that hormones themselves do not often cause variation in behaviour but rather act as modulators or permissive agents. According to Becker, et al. (1992) variation in behaviour among individuals is related to the variations in the level of hormones present in an individual’s endocrinal system such as the increased sexual receptiveness in women during menstruation. These bodily variations lead to a behavioural change such as cognitive task performance, mood swings, sexual activity or even sensory sensitivity.
Influence of Androgens on Male Behaviour
In men, androgens, specifically testosterone, have been shown to influence dominance-related behaviour such that men having a higher level of testosterone are usually more aggressive and competitive (Sheri A. B. (2002). Androgen is a steroid hormone that is responsible for the control or stimulation of the development and maintenance of characteristic features in males through binding to androgen receptors. Androgens are among a group of sex steroids in humans and the major androgen is the testosterone (DHEA) and they usually impact on a range of physiological behavioural manifestations as well as sexual and reproductive processes that impact on human behaviour. Androgens are produced in higher amounts in men than in women at puberty; same time when males exhibit higher levels of aggressiveness than women (Wilson, 1999). In men, testosterone level varies frequently since it is usually released into the bloodstream in spurts. It is imperative to note that brain’s sexual dedifferentiation is paramount for the differentiation into either a male or female.
Testosterone and male aggressiveness
In men, testosterone has been noted to be the key factor determining agonistic behaviour and which studies have shown to be at its peak during the pubertal stage. According to Carter (1997) recent research on free salivary testosterone levels has identified a high correlation with a range of aggressive behaviors in normal males. Similar correlation has been identified with the free cerebral spinal fluid levels of testosterone in criminals. This is supported by studies showing testosterone correlation among aggressive inmates and levels of steroids in circulation in their systems. Different studies indicate that the implications of testosterone are more pronounced when studied in group rather than individually. For instance, in fraternity, the unruly behaviour demonstrated by men has been found to be associated with the levels of saliva testosterone. In a study of groups, groups whose average testosterone levels are relatively lower were found to be friendlier than groups with high testosterone levels. DHEA, a weaker androgen as well as androgen therapy have been shown to reduce aggressiveness (Becker, et al. 1992). This effect has been the focus of the study of the use of anabolic androgenic steroids. Testosterone also has a mascularnizing impact which is important in male behaviour. Studies on human aggression faces the challenge associated with time lapse between when the moment when an aggressive act is performed and the time of testing the testosterone levels.
While increasing aggressiveness, testosterone also leads to an elevation of dominance behaviour. It has been scientifically proven that the level of testosterone is the major requisite for male’s aggressive behaviors, with the highest extent of aggressiveness been identified in males with the highest levels of testosterone hormone, mostly young men (Archer, 1991). Some studies indicate that behavioural changes in certain states do trigger hormonal changes. However, the subject of aggression is more complex than just the sole focus on one hormone as has been the case with testosterone studies. Testosterone studies have been the basis of the use of anti-androgenic drugs including medroxyprogesterone to reduce problematic sexual behaviour while lowering the levels of blood testosterone by about 50 % to 75 % although other behaviors are not affected. This is supported by the evidence observed in differences in sexual aggressiveness widely witnessed in young males just before puberty (Breedlove, et al. 2007). Among teenagers of the same age, sexual aggression cases are more prevalent in boys than girls.
Influence of Hormones on Female Sexual Behaviour
In humans, sexual behaviour has been found to be the function of steroid hormones. A review of literature on the impact of ovarian hormones shows that sexual drive is influenced by the events occurring during the menstrual cycle as well as endocrine events mainly involving the variation of progesterone or estrogen hormones (Schmitt, 1997). However, natural social systems also have been noted to influence female sexual behaviour especially within environments where females are free to follow their social and sexual choices. Changes in sexual behaviour have been observed during the period of ovulation. Human females have been identified to manifest increased sexual interest and/or activity during mid-cycle period of menstruation. Sexual behaviour in females thus tends to vary with menstruation cycles.
Estrogen
Estrogen, one of the female hormones involved in menstruation greatly affects the motivations towards sex in female humans. This is associated with the high levels of sexual behaviour exhibited by females during the follicular stage of menstruation. Decline in estrogen production during menopause is linked to the declined sexual activity in some women after the menopause stage (Donovan, 1985). Research shows that estrogen is responsible for normalizing patterns of sleep, preventing hot flashes or even increasing lubrication of the vagina; factors which are positively correlated with increased sexual behaviour. Estrogen is also associated with an increase in peripheral changes such as bodily odors that increase a female’s sexual attractiveness to male partners (Whalen, 1977).
Progesterone
Progesterone production is usually at peak secretion during ovulation and luteal phases of the menstruation period in human females. It has been found out that a short lasted exposure to progesterone increases sexual activity in women. This explains the reason for the increased sexual activity in some female humans using oral contraceptives, as these contraceptives are basically synthetic and contain progestin (Crenshaw & 1996). Prolonged exposure to progesterone on the other hand has been found to lower sexual activity. This is because progesterone has the potential to act as an anti-androgenic whose impact leads directly to inhibition of motivation of females towards sexual activity. This has been confirmed by studies in human females using administered progestin.
Androgen
During the menstruation cycle, human females show unstable interests in sexual activity. This has been identified to be partly contributed by the effect of increased secretion of androgens by both the adrenal gland and the ovary. Studies have confirmed that during the same time, women report increased sexual interest and activity especially at periods just before the onset of menstruation and after (Greenspan, 1994). This is because androgen production is at peak levels at this time. Andrenalectomy, related with the production of androgen by the adrenal cortex is known to inhibit to sexual activity in females. Impact of treatment with androgens on the sexual behaviour of females has been of particular interest in medical research recently. While it increases aggressiveness in men, androgen leads to a reduced sexual activity in women.
Conclusion
A lot has been documented concerning influence of hormones on human behaviour. Major behaviors controlled by hormones encompass: sexual behavior in both males and females, parental behaviour, menopause, partnering between members of the opposite sex including activities such as courting. It is apparent that hormones are of great importance in human life as without them these behavioural processes would be adversely affected. However, environmental factors also play an immense role in the manifestation of these behaviors. It is thus apparent that more studies ought to be done to address problems associated with hormonal differences and/or failure to control certain behaviors.
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