Реферат: Impact of Evolution on Human Thought. Testosterone
Impactof evolution on human thought
For a long periodof time humans could not answer the question of what makes a man, a man, and awomen, a women. As was recently foundmain difference is not just in presence of genitals. Probably one will ask why? The answer is that genitals themselves areindirect products of another matter. Thename of this matter is testosterone.
“Testosterone is a hormone thatstimulates sexual development in male human beings. It belongs to a family of hormones calledandrogens. Primarily the testicles, apart of male sex glands, produce androgens. The ovaries in females and the adrenal glands in both sexes also yieldsmall amounts of testosterone and other androgens (The world book encyclopedia).”
In its earliestcrucial functions, in developing embryo, testosterone play the key role intelling the cells of the genetically male embryo to develop as a male. It is amazing, but all human embryo begins asfemales for the first few weeks of an embryo’s life, a small group of cellshave potential to develop either as ovaries or testes. About one million of genes that are needed todirect the development of a human being, one single gene (the “SRY” gene), whichis carried on the Y chromosome, is responsible for determining the sex of theembryo. If the embryo’s cells containthe “SRY” gene, the embryo will develop testes, which at some point and for alimited period of time early in its development produce and release a bigamount of testosterone. It turn, testosterone then signal the cells ofother parts of the embryo to develop as a male.
As shown in thestudy by a Stanford research group namely testosterone is responsible forformation of genitals. An experiment washeld on newborn female rats. They wereinjected with testosterone. Surprisingly, but the female rats developed male genitals, and femalegenitals began disappearing. Later“converted” female rats started revealing purely male behavior, and they werefully aware of usage of their “new” male genitals. The same experiment was performed with malenewborn rats. It is amazing, but theirpenises withered and later completely disappeared. This experiment is not ethical to perform onhumans, but random facts suggest that all most the same can be done withhumans. For instance, in lesbian couple,butches (female that represents male) use testosterone injections to developmale features such as deep voice, facial hair and muscles (“The He Hormone,”Andrew Syllivan)
In girls, theadrenal glands begin to produce testosterone earlier than in boys. That’s is how and why girls mature earlier,as a rule, than boys. It wastestosterone that stimulated the growth of girls pubic hair and underarm hair(there are testosterone receptors in the skin of the pubic area and the skin ofthe underarm that are genetically programmed to react to testosterone byproducing hair). And testosteronestimulated girls skin to produce more oil, contributing to the acne of girlsearly teenage years, but also to the healthy glow of the skin and the shine ofthe hair.
The medical bookReproductive Endocrinology by Drs. Samuel Yen and Rovert Jaffe, states; “Testosterone and other androgens have somebiological activity o virtually every tissue in the body.” Among the most important functions listed are“anabolic actions, such as stimulation of linear body growth, nitrogenretention, and muscular development.” This statement means that testosterone works to keep the cells of thebody functioning efficiently, making the best use of nourishment of growth andmaintenance, and particularly contributing to the health of bones andmuscles.
Having knowledge of the waytestosterone function in the body, artificial testosterone injections can beused for variety of purposes. One of thepurposes of artificial use of testosterone is to stimulate sex drive. The balance of this hormone is responsiblefor initiating and maintaining the production of sperm from early pubertythroughout adulthood in male body. During childhood and adolescence, these hormones are responsible for:
1)<span Times New Roman"">Growth ofgenitals
2)<span Times New Roman"">Depth of pitch ofthe voice, increase muscle mass, and growth of bones.
3)<span Times New Roman"">Appearance of thebody and facial hair.
Overproduction oftestosterone caused by testicular, adrenal, or pituitary tumors in the youngmale may result in precocious puberty. Overproduction of testosterone in females, caused by ovarian and adrenaltumors, can result in muscessation of the menstrual cycle and excessive growthof body hair. Level of testosterone arelow before puberty; they begin to increase at the onset of puberty and continueto increase during adulthood. Productionbegins to diminish at about age of 40, eventually dropping to about one-fifthof the peak level by age of 80 (“Hormone of desire,” Susan Rako).Scientifically established men’s testosterone, level is at least ten timeshigher than any of the women. Accordingto the last available date, even male population accounts for less than 50percent of the world’s population, major part of violence is perpetrated bymen.
Currently many males usetestosterone shots or gel for the purpose of body-building. Testosterone shots trigger imbetterment ofappetite and muscles growth. Besides,testosterone can have effects on the function of several brain areas. One additional surprising effect oftestosterone is that it can not only affect the function of the brain but alsoits development and anatomy. Study inlaboratory of Roger Gorskis at the University of California, Los Angeles, hasrevealed that the sex difference in the brain anatomy appears to be due to thepresence of male sex hormones at a certain stage of brain development in malerats. Later work has shown a similareffect of testosterone at other brain areas: for example, the spinal nerve cells that control the muscles of thegenital area are more numerous in male rats (cross sections through thehypothalamus of a male and female rats (male, (thinner and longer)).
Below is a human lifeexample how hormone level can influence human health, and behavior brought byJohn K. Young in his book “Hormones; molecular messenger.”
“Bridget was divorcing Bob, her husband of tem years, so she was notterribly surprised when she started to feel anxious and upset upon awakening inthe morning. She grew worried, however,when these anxiety attacks became more frequent and stronger, coming upon herat all times of the day. She went tosee a psychiatrist. The doctor alsoassumed the problem was stemming from her divorce proceedings and prescribed anantidepressant. After two weeks of moreanxiety and no relief coming from the dedication, Bridget felt like committingherself to a institution. Hernervousness was now even making her hair fall out; her skin began to feel thinand bruised. She was not eatingproperly either, but was surprised to see she had lost over twenty pounds.
One night Bridget’s best friend Virginia invited her to a dinnerparty. Over the meal, someone mentionedhow traumatic divorce was; Bridget laughingly said that it was not making herthin and anxious, it was also thinning out her skin and hair. One of the other guests, a young woman, askedher to elaborate, and Bridget shyly told her the symptoms she had beensuffering from. The young woman thenintroduced herself as a doctor. Sheasked Bridget to come down to her office for a few tests. Bridget did and these tests revealed what thedoctor had first suspected; that Bridget was not suffering from a psychiatricdisorder, but rater a hormonal one. Herthyroid gland was overworking, giving her the symptoms of thinning hair, thinskin, excessive weight loss, and anxiety. Afte4r treatment all of Bridgets’ symptoms disappeared.”
The exampledescribed above suggests that level of testosterone influence not only physicaldevelopment of the body, but also is responsible for emotions andbehavior. One researcher, curios aboutthe fact that only male canaries sing during mating season, gave a testosteroneshot to female canaries. The result wasamazing, the female canaries “burst into song.” The same experiment was performed on zebra finches. Dr. Christina Wang’s study reveals that menwith low testosterone level are irritable and aggressive than those withhigh-normal level. “When theirtestosterone level was increased during hormone-replacement therapy, theiranger diminished and their sense of well-being increased.”
Robert M.Sapolsy, in his book “The trouble with testosterone,” takes opposite opinionside to scientists who think that increasing testosterone level leads tochanges in behavior (such as becoming more aggressive). He holds an opinion that changes insurrounding environment trigger change in the level of testosterone.
“Okay, suppose you note a correlation between levels of aggression andlevels of testosterone among these normal males. This could be because (a) testosteroneelevates aggression; (b) aggressionelevates testosterone secretion; (c)neither cause the other. There is a hugebias to assume opinion (a), while (b) is the answer. Study after study has shown that when youexamine testosterone levels when males are first placed together in the socialgroup testosterone levels predict nothing about who is going to beaggressive. The subsequent behavioral differencesdrive the hormonal changes, rather the other way around (“Trouble withTestosterone,” pp. 152).”
It is a goodpoint, but what about evidences suggesting that men after taking testosteroneinjection find themselves more aggression than normally. The article “The He Hormone” by AndrewSullivan brings a good example when a man after taking testosterone shot couldnot control his increased aggressiveness and “had nearly gotten into the firstpublic brawl of his life.”
“Soon after I inject myself with testosterone I feel a deep surge ofenergy. My attention span shortens. My wit is quicker, my mind is faster, but myjudgement is more impulsive.”
Several other studies suggest that individuals withwinning attitudes have higher testosterone levels, at least for a short periodof time, than those without such an attitude. One group of researchers, for example, measured testosterone levels insix college tennis players and found that testosterone levels began to rise inall of them before their matches, apparently in anticipation of competition. The big surprise came after the fact: the testosterone levels of those who wontheir matches remained high, while the testosterone levels of those who lostdiminished.
A second group of researchers, at North Dakota StateUniversity in Fargo, undertook even further step by trying to figure out if itwas the competition itself, or the mood produced by winning, that caused therise in testosterone. In theirexperiment, male college students either won or lost $5 through a series ofcoin tosses. The task removed allelements of skill or competition; blind luck determined winners andlosers. After the tosses had beenfinished, the researchers measured the saliva of participants for changes intheir testosterone levels. Those who wonmoney experienced a more positive mood and a rise in “test”; those who lostwhose a decrease in the later. Theresult suggested that the acts of winning, rather than the nature of thecompetition or the skill involved, improve mood and produces an increase intestosterone levels. This experimentobviously supports Robert’s Saporky statement that testosterone level changeswith external factors.
Two more recent studies by a single group of researcherswent further to find out if one has to directly participate in competing inorder to experience increase in testosterone level. In the first study, theresearchers measured the salivary testosterone levels of fans who attended acollege basketball game. In another,they took the same measurement of a group who watched a World Cup soccer matchon television. In each study,testosterone levels were taken before and after the game. In both experiments, those fans whose teamhad won experienced a surge in their testosterone levels, while those fanswhose team had lost showed a drop.
The result wasvery surprising. Even the fans are notdirectly involved in the competition, the their testosterone levels change inaccordance with whether their team is losing or winning. The supervisor of the researches, a doctoralcandidate in education psychology at the University of Utah in Salt Lake City,makes a comment on the researches notes: “Fans do not have much to do with outcome: there are more like voyeursto the team’s experience of competition.” Nonetheless, experiencing victoryeven vicariously apparently has very real effect on a person’s hormone levels.
Testosteronelevel is not only different among individuals, but it changes within oneorganism one intraday basis. Testosterone level can vary by up to fifty percentduring one day. In the mornings it tendsto be higher than in the evenings. Thisis another reason why people feel fresh in the mornings. During the day onemight experience ups and downs of testosterone level induced by winning moodeffect. These up and downs do not haveeffect on physical development of the individual (“The Testosterone Syndrome,”Eugene Shippen, William Fryer).
Sensitivity tothe changes in the testosterone levels is not very researched subject. It is noticed that different individualsexperience different effects after having the same amount of testosteroneinjected. The genetically determined differences in the numbers of testosteronereceptors may be one factor.
Besidesstimulating growth of bones, body mass, facial hair, change in voice,testosterone might be a possible reason of illnesses. In the report by Paule A.Lotufo, Joann E. Manson, Alexandersen P, Haarbo J, Christiansen C., on malepattern baldness and coronary heart disease, the authors conclude that “vertexpattern baldness appears to be a marker for increased risk if coronary heartdisease. They state that testosteronemay provide a “plausible explanation for an association between baldness andcoronary heart disease.” The referencecited is a study that shows elevated testosterone levels in men with prostatecancer and baldness; however, these were no measured testosteroneconcentrations in the data presented. Dr. Brian L.G. Morgan and Roberta Morgan, in their book “Hormones,” aretying to link high testosterone level with coronary heart disease. They bring into attention the fact that ingeneral, since women have lower testosterone levels than men, according toavailable poll of data, they live longer lives. “Equal numbers for both sexes are around by age thirty, and only 70percent of men reach age sixty-five, where as 84 percent of women do.”
On the contraryrecent results from the Telecom Study showed that decreased testosterone levelswere associated with increased cardiovascular risk factors in otherwise healthymen.
Eugene Shippenand William Fryer, in their book “Testosterone syndrome,” agree with theopinion that low level of testosterone are more associated with increasedcardiovascular risk factors, rather than all the way around.
“The fundamental fact is this: a clear and ever-increasing majority ofmedical studies report an association between high testosterone and lowcardiovascular disease in men. This isnot a coincidental association, since when testosterone is diminishedwell-accepted risk factors increase, and when testosterone is administered inappropriate doses most of the major risk factors for heart diseasediminish. Moreover, in the majority ofpatients, symptoms and objective EKG measurements improve. These studies are confirming the results Ihave been getting with patients for years. Men prosper health wise and live longer when their testosterone levelsare normal. Heart problems, inparticular, are more easily controlled (The Testosterone Syndromes, pp. 81).”
With growing old,men begin experiencing erective problems and losing sexual interest. These problems are caused by diminishment intestosterone level. Facts reveal thatmen who are taking testosterone, in any form, experience surge of sexualinterest, and overall enhancement in physical strength. Eugene Shippen, and William Fryer, in theirbook “The Testosterone Syndrome,” relate diminishing sexual interest to a signof future heart disease and diabetes, conditions common in the male menopause(“The Testosterone Syndrome,” pp. 59)
At the end ofthis research, I would like to notice and bring example of the fact thatmajority of scientific world hold opinion that artificial testosterone ifcorrectly applied can bring much of good to the human kind, especially toelderly.
“Standford R. isseventy-four years old now, but he has had heart problems since the early1970s. It did not make life easy forhim. He is an athletic man who likes tohunt, fish on the river, and walk in the woods. By the time Standford together with his chest pains, got into the 1980s,it was time for a quintuple bypass. Thechest pains started up again in a few years later. His chest pains went away, his energyreturned and when he is not walking over the hills and fields and hunting inthe woods, Standford makes love. Sometimes twice a day (“The Testosterone syndrome,” pp79).
As can beconcluded from all researches discussed above change in testosterone leveltriggers changes in behavioral pattern, and environmental change followed bychange in behavioral pattern triggers change in testosterone level.
The arguments inscientific world regarding testosterone and their role in human anatomy are notover yet. The subject is hard toexplore, because experiments that has to be done in order to find right answersare not considered to be ethical on humans. The scientific world has no choice, but to use random historical factsto come to the answers. However, thefact the testosterone play a huge role in human development and behavior is notargued by any more.
1)<span Times New Roman"">“The Testosterone Syndrome”;Eugene Shippen, M.D. and William Fryer, M. Evans and Company, Inc., 1998
2)<span Times New Roman"">“Hormones; MolecularMessenger”; John K. Young, Franklin Watts, 1994
3)<span Times New Roman"">“The Trouble with Testosteroneand other essays on the biology of the human predicament”; Robert M. Sapolsky,Scribner, 1997
4)<span Times New Roman"">“The Hormone of Desire; The Truth about sexuality, menopause, andtestosterone”; Susan Rako, M.D., Harmony Books, 1996
5)<span Times New Roman"">“Never Too Buff”; John Cloud
6)<span Times New Roman"">“The He Hormone”; AndrewSullivan