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Hormones associated to aggression during human development--论文代写范文
2016-04-15 来源: 51due教员组 类别: Essay范文
而青春期急剧增加,经常在月经周期的阶段之后。与所观察到的睾丸水平,目前没有证据表明任何胎儿卵巢激素产生作用的。他们也有一个重要的角色在成熟的生殖器官和次要性的角色。下面的essay代写范文进行论述。
Abstract
Only a few of these above mentioned hormones have been found to have some relationship with aggression during human development: gonadal and adrenal androgens, and perhaps and in minor degree also gonadotrophins, prolactine, and estrogens. Let us here attempt to review what has been reported in the scientific literature.
Brief information about hormones during human development
The main androgen or male sex hormone is T. Its secretion rises in three periods of life: an early first peak in the fetus from about 11 postmenstrual weeks probably till birth, time when it falls rapidly (during this time it causes differentiation of the external genitalia and of the hypothalamus in an male type); a second peak about 2 months after birth lasting a few months (its function is still unknown); and a third very large peak at puberty (growth, maturation of genital organs, and appearance of secondary sex characters), first becoming apparent between 10 and 12 years of age, requiring a joint action with GH for its full effect on the adolescent growth spur. In humans, androgens have been described, albeit inconsistently, to play a role in the regulation of sexuality, aggression, cognition, emotion, and personality. The female sex hormone is E. It begins to be secreted by the ovaries very early in life, long before puberty, at low levels during childhood, increasing sharply at puberty, and fluctuating regularly thereafter with the phase of the menstrual cycle. Contrary to what has been observed in the testes (a prenatal peak of T), there is no evidence of any hormonal action by the ovary of the fetus. They also have an important role on maturation of genital organs and appearance of secondary sex characters.
Report of the studies
Given the dramatic changes that occur in endocrine physiology at puberty, it is not surprising that increases in testosterone are hypothesized to be related to increases in aggression. This explains why T has been the most investigated hormone in its research. The wealth of evidence supporting the ability of T to facilitate aggressive behavior in a broad number of mammal species has led to wonder about its potential role in human aggression, expecting at least a positive correlation between both variables.
These studies, however, yielded equivocal results. Even if elevated circulating T levels have been reported in some antisocial youth, the T-aggression link is not consistently reported across studies in children and adolescents. Archer (1991) conducted three meta-analyses, including only five to six studies, and found a weak, positive relationship between T and aggression. Another recent meta-analysis based on 45 independent studies with 54 independent effect sizes re-examined this relationship (Book et al., 2001), and found a range of correlations from .28 to .71. This mean weighted correlation (r =.14) corroborates Archer’s finding of a weak positive relationship. The first study to show the activational influences of circulating T and aggression in adolescents was done with 15–17-year-old boys.
Aggression in response to hypothetical provocation was measured by self-reports. A direct and longitudinal effect of T on aggression was shown: a higher T level led to an increased readiness to respond to provocation, but T had no direct effect on unprovoked aggression (Olweus, Mattson, Schalling, & Low, 1980, 1988). A second study designed to analyze puberty-related psycho-biological processes in 10–14- year-old girls examined, among other aspects, whether hormonal pubescent changes were more likely to be associated with negative affect, measuring self-reports of emotional states and a hormonal assessment in serum of LH, FSH, E, T, DHEAS, and CORT. Aggressive affect was negatively associated with DHEAS, but no relations with T were found (BrooksGunn & Warren, 1989; Warren & Brooks-Gunn, 1989).
A third study was a NIMH-NICHD collaboration that analyzed, among other aspects, the relations between serum levels of adrenal and gonadal hormones (LH, FSH, T, E, DHEA, DHEAS, D4-A, and CORT) and mother-reported aggressive attributes in 56 boys and 52 girls, age 9–14 years. The general pattern of findings in boys only, but not in girls, was a higher level of delinquent behavior related to lower DHEAS and T/E2 ratio, and a higher rebellious attitude related to higher levels of LH, lower levels of FSH, and higher levels of DHEA (Susman et al., 1987). Another aspect focused on was the expression of anger of young adolescents while interacting with their parents during problem-solving tasks. The expression of anger was related to a consistent relationships with D4-A, which will be commented later, and to higher levels of hormones that increase at puberty, especially with regard to E in girls. The interpretation would be that young adolescent girls may be very sensitive to changes in E level, as is also hypothesized during the menopausal period (InoffGermain et al., 1988). From the same sample, adjustment problems were also associated with a hormone profile similar to that described for aggressive attributes: higher D4-A and lower T levels or a lower T/E ratio (Nottelmann et al., 1987).
T levels could be a signal of social success rather than of physical aggression, as suggested first by Sapolsky (1991), examining experiential influences on T and CORT secretion in male baboons in natural environment, concluded that aggressiveness and social status were associated with higher T, while subordinates were with lower levels, and more recently in human adolescents by Schaal, Tremblay, Soussignan, and Susman (1996) in a study that analyzed the association of male pubescent T with social dominance and physical aggression. Boys perceived as socially dominant by unfamiliar peers, from age 6 to 12, were found to have concurrently higher levels of T at age 13 than boys perceived as less socially dominant In contrast, boys who had a history of high physical aggression, during the same age range, had lower T levels at age 13 compared with boys with no such a history.
T levels therefore were positively associated with social success rather than with physical aggression. High T levels in adolescent boys may thus be regarded as a marker of social success in a given context, rather than of social maladjustment as suggested in previous studies. Adolescents may try to gain social status through dominance and leadership, using aggressive and assertive methods. If successful, T is expected to increase, and if unsuccessful, T would decrease because the negative status associated with failure. Another question posed was whether chronically aggressive and impulsive behavior affects hormone concentrations in adolescents during their developmental transitions. Hormone determinations in serum and saliva and several self-report tests were applied to Caucasian rural adolescents, either experiencing transition to puberty (boys: mean age = 12.7 and girls: mean age = 11.9) and experiencing transition to pregnancy (girls: mean age = 17.4). An analysis of hormone-behavior connections showed concurrent relationships, indicating individual differences in hormone concentration as possible influences on behaviors.
Experience and behavior may also be implicated on hormone concentrations, changing the endocrine milieu. Subtle variations in timing of puberty related to experience may predispose some adolescents to aggression and violent behavior, and to other wrong coping strategies, such as heavy drinking. Also late maturing males experience difficulty in attaining dominance and peer popularity because their immature physical status (Susman, Worrall, Murowchick, Frobose, & Schwab, 1996). A cross-cultural comparison within American white male adolescents (Cohen, Nisbett, Bowdle, & Schwarz, 1996) also revealed that norms characteristic of a ‘culture of honor’ manifested themselves not only in the cognitions, emotions, and behaviors, but also in the physiological reactions of the subjects. Whereas Northerners were relatively unaffected when insulted, Southerners were more upset (as shown by a rise in CORT levels), and more physiologically primed for aggression (as shown by a rise in T levels). BLOOD? In another research, salivary T and CORT levels were also measured in 29 violent delinquents and 36 U.S. college students of a similar age.
The delinquents had higher T levels but did not differ regarding CORT (Banks & Dabbs, 1996). The first study to causally relate the administration of physiological doses of sex steroids to changes in aggressive behaviors in adolescents, focused on the role of sex steroids in the development of aggressive behaviors in hypogonadal adolescents (Finkelstein et al., 1997). Depo-testosterone (to 35 boys) or conjugated estrogens (to 14 girls) was administered in 3- month blocks alternating with placebo at three dose levels approximating early, middle and late pubertal amounts, and the Olweus Multifaceted Aggression Inventory was applied after each period. Results demonstrated significant hormonal effects on physical aggressive behaviors and aggressive impulses, but not on verbal aggressive behaviors nor on aggressive inhibitions in both boys and girls. The fact that physical aggression was affected whereas the verbal was not, could been explained at least partially by the changes in musculature also observed.(essay代写)
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