Impact of Evolution on Human Thought. Testosterone
of evolution on human thought
For a long period of time humans could not answer the
question of what makes a man, a man, and a women, a women. As was recently
found main difference is not just in presence of genitals. Probably one will
ask why? The answer is that genitals themselves are indirect products of
another matter. The name of this matter is testosterone.
“Testosterone is a hormone that stimulates sexual
development in male human beings. It belongs to a family of hormones called
androgens. Primarily the testicles, a part of male sex glands, produce
androgens. The ovaries in females and the adrenal glands in both sexes also
yield small amounts of testosterone and other androgens (The world book
In its earliest crucial functions, in developing
embryo, testosterone play the key role in telling the cells of the genetically
male embryo to develop as a male. It is amazing, but all human embryo begins
as females for the first few weeks of an embryo’s life, a small group of cells
have potential to develop either as ovaries or testes. About one million of
genes that are needed to direct the development of a human being, one single
gene (the “SRY” gene), which is carried on the Y chromosome, is responsible for
determining the sex of the embryo. If the embryo’s cells contain the “SRY”
gene, the embryo will develop testes, which at some point and for a limited
period of time early in its development produce and release a big amount of
testosterone. It turn, testosterone then signal the cells of other parts of
the embryo to develop as a male.
As shown in the study by a Stanford research group
namely testosterone is responsible for formation of genitals. An experiment
was held on newborn female rats. They were injected with testosterone.
Surprisingly, but the female rats developed male genitals, and female genitals
began disappearing. Later “converted” female rats started revealing purely
male behavior, and they were fully aware of usage of their “new” male
genitals. The same experiment was performed with male newborn rats. It is
amazing, but their penises withered and later completely disappeared. This
experiment is not ethical to perform on humans, but random facts suggest that
all most the same can be done with humans. For instance, in lesbian couple,
butches (female that represents male) use testosterone injections to develop
male features such as deep voice, facial hair and muscles (“The He Hormone,”
In girls, the adrenal glands begin to produce
testosterone earlier than in boys. That’s is how and why girls mature earlier,
as a rule, than boys. It was testosterone 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 of the underarm that are genetically programmed to
react to testosterone by producing hair). And testosterone stimulated girls
skin to produce more oil, contributing to the acne of girls early teenage
years, but also to the healthy glow of the skin and the shine of the hair.
The medical book Reproductive Endocrinology by Drs.
Samuel Yen and Rovert Jaffe, states; “Testosterone and other androgens have
some biological activity o virtually every tissue in the body.” Among the most
important functions listed are “anabolic actions, such as stimulation of linear
body growth, nitrogen retention, and muscular development.” This statement
means that testosterone works to keep the cells of the body functioning
efficiently, making the best use of nourishment of growth and maintenance, and
particularly contributing to the health of bones and muscles.
knowledge of the way testosterone function in the body, artificial testosterone
injections can be used for variety of purposes. One of the purposes of
artificial use of testosterone is to stimulate sex drive. The balance of this
hormone is responsible for initiating and maintaining the production of sperm
from early puberty throughout adulthood in male body. During childhood and
adolescence, these hormones are responsible for:
Growth of genitals
Depth of pitch of the voice,
increase muscle mass, and growth of bones.
Appearance of the body and facial
of testosterone caused by testicular, adrenal, or pituitary tumors in the young
male may result in precocious puberty. Overproduction of testosterone in
females, caused by ovarian and adrenal tumors, can result in muscessation of
the menstrual cycle and excessive growth of body hair. Level of testosterone
are low before puberty; they begin to increase at the onset of puberty and
continue to increase during adulthood. Production begins to diminish at about
age of 40, eventually dropping to about one-fifth of the peak level by age of
80 (“Hormone of desire,” Susan Rako). Scientifically established men’s
testosterone, level is at least ten times higher than any of the women.
According to the last available date, even male population accounts for less
than 50 percent of the world’s population, major part of violence is
perpetrated by men.
many males use testosterone shots or gel for the purpose of body-building.
Testosterone shots trigger imbetterment of appetite and muscles growth.
Besides, testosterone can have effects on the function of several brain areas.
One additional surprising effect of testosterone is that it can not only affect
the function of the brain but also its development and anatomy. Study in
laboratory of Roger Gorskis at the University of California, Los Angeles, has
revealed that the sex difference in the brain anatomy appears to be due to the
presence of male sex hormones at a certain stage of brain development in male
rats. Later work has shown a similar effect of testosterone at other brain
areas: for example, the spinal nerve cells that control the muscles of the
genital area are more numerous in male rats (cross sections through the
hypothalamus of a male and female rats (male, (thinner and longer)).
is a human life example how hormone level can influence human health, and
behavior brought by John K. Young in his book “Hormones; molecular messenger.”
divorcing Bob, her husband of tem years, so she was not terribly surprised when
she started to feel anxious and upset upon awakening in the morning. She grew
worried, however, when these anxiety attacks became more frequent and stronger,
coming upon her at all times of the day. She went to see a psychiatrist. The
doctor also assumed the problem was stemming from her divorce proceedings and
prescribed an antidepressant. After two weeks of more anxiety and no relief
coming from the dedication, Bridget felt like committing herself to a
institution. Her nervousness was now even making her hair fall out; her skin
began to feel thin and bruised. She was not eating properly either, but was
surprised to see she had lost over twenty pounds.
One night Bridget’s
best friend Virginia invited her to a dinner party. Over the meal, someone
mentioned how traumatic divorce was; Bridget laughingly said that it was not
making her thin and anxious, it was also thinning out her skin and hair. One
of the other guests, a young woman, asked her to elaborate, and Bridget shyly
told her the symptoms she had been suffering from. The young woman then
introduced herself as a doctor. She asked Bridget to come down to her office
for a few tests. Bridget did and these tests revealed what the doctor had
first suspected; that Bridget was not suffering from a psychiatric disorder,
but rater a hormonal one. Her thyroid gland was overworking, giving her the
symptoms of thinning hair, thin skin, excessive weight loss, and anxiety.
Afte4r treatment all of Bridgets’ symptoms disappeared.”
The example described above suggests that level of
testosterone influence not only physical development of the body, but also is
responsible for emotions and behavior. One researcher, curios about the fact
that only male canaries sing during mating season, gave a testosterone shot to
female canaries. The result was amazing, the female canaries “burst into
song.” The same experiment was performed on zebra finches. Dr. Christina
Wang’s study reveals that men with low testosterone level are irritable and
aggressive than those with high-normal level. “When their testosterone level
was increased during hormone-replacement therapy, their anger diminished and
their sense of well-being increased.”
Robert M. Sapolsy, in his book “The trouble with
testosterone,” takes opposite opinion side to scientists who think that
increasing testosterone level leads to changes in behavior (such as becoming
more aggressive). He holds an opinion that changes in surrounding environment
trigger change in the level of testosterone.
It is a good point, but what about evidences
suggesting that men after taking testosterone injection find themselves more
aggression than normally. The article “The He Hormone” by Andrew Sullivan
brings a good example when a man after taking testosterone shot could not
control his increased aggressiveness and “had nearly gotten into the first
public brawl of his life.”
“Soon after I inject
myself with testosterone I feel a deep surge of energy. My attention span
shortens. My wit is quicker, my mind is faster, but my judgement is more
other studies suggest that individuals with winning attitudes have higher
testosterone levels, at least for a short period of time, than those without
such an attitude. One group of researchers, for example, measured testosterone
levels in six college tennis players and found that testosterone levels began
to rise in all of them before their matches, apparently in anticipation of competition.
The big surprise came after the fact: the testosterone levels of those who won
their matches remained high, while the testosterone levels of those who lost
second group of researchers, at North Dakota State University in Fargo,
undertook even further step by trying to figure out if it was the competition
itself, or the mood produced by winning, that caused the rise in testosterone.
In their experiment, male college students either won or lost $5 through a
series of coin tosses. The task removed all elements of skill or competition;
blind luck determined winners and losers. After the tosses had been finished,
the researchers measured the saliva of participants for changes in their
testosterone levels. Those who won money experienced a more positive mood and
a rise in “test”; those who lost whose a decrease in the later. The result
suggested that the acts of winning, rather than the nature of the competition
or the skill involved, improve mood and produces an increase in testosterone
levels. This experiment obviously supports Robert’s Saporky statement that
testosterone level changes with external factors.
more recent studies by a single group of researchers went further to find out
if one has to directly participate in competing in order to experience increase
in testosterone level. In the first study, the researchers measured the
salivary testosterone levels of fans who attended a college basketball game.
In another, they took the same measurement of a group who watched a World Cup
soccer match on television. In each study, testosterone levels were taken
before and after the game. In both experiments, those fans whose team had won
experienced a surge in their testosterone levels, while those fans whose team
had lost showed a drop.
The result was very surprising. Even the fans are not
directly involved in the competition, the their testosterone levels change in
accordance with whether their team is losing or winning. The supervisor of the
researches, a doctoral candidate 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 voyeurs to the team’s
experience of competition.” Nonetheless, experiencing victory even vicariously
apparently has very real effect on a person’s hormone levels.
Testosterone level is not only different among
individuals, but it changes within one organism one intraday basis.
Testosterone level can vary by up to fifty percent during one day. In the
mornings it tends to be higher than in the evenings. This is another reason
why people feel fresh in the mornings. During the day one might experience ups
and downs of testosterone level induced by winning mood effect. These up and downs
do not have effect on physical development of the individual (“The Testosterone
Syndrome,” Eugene Shippen, William Fryer).
Sensitivity to the changes in the testosterone levels
is not very researched subject. It is noticed that different individuals
experience different effects after having the same amount of testosterone
injected. The genetically determined differences in the numbers of testosterone
receptors may be one factor.
Besides stimulating 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 male pattern baldness and coronary heart disease, the
authors conclude that “vertex pattern baldness appears to be a marker for
increased risk if coronary heart disease. They state that testosterone may
provide a “plausible explanation for an association between baldness and
coronary heart disease.” The reference cited is a study that shows elevated
testosterone levels in men with prostate cancer and baldness; however, these
were no measured testosterone concentrations in the data presented. Dr. Brian
L.G. Morgan and Roberta Morgan, in their book “Hormones,” are tying to link
high testosterone level with coronary heart disease. They bring into attention
the fact that in general, since women have lower testosterone levels than men,
according to available poll of data, they live longer lives. “Equal numbers
for both sexes are around by age thirty, and only 70 percent of men reach age
sixty-five, where as 84 percent of women do.”
On the contrary recent results from the Telecom Study
showed that decreased testosterone levels were associated with increased
cardiovascular risk factors in otherwise healthy men.
Eugene Shippen and William Fryer, in their book
“Testosterone syndrome,” agree with the opinion that low level of testosterone
are more associated with increased cardiovascular risk factors, rather than all
the way around.
“The fundamental fact
is this: a clear and ever-increasing majority of medical studies report an
association between high testosterone and low cardiovascular disease in men.
This is not a coincidental association, since when testosterone is diminished
well-accepted risk factors increase, and when testosterone is administered in
appropriate doses most of the major risk factors for heart disease diminish.
Moreover, in the majority of patients, symptoms and objective EKG measurements
improve. These studies are confirming the results I have been getting with
patients for years. Men prosper health wise and live longer when their
testosterone levels are normal. Heart problems, in particular, 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
in testosterone level. Facts reveal that men who are taking testosterone, in
any form, experience surge of sexual interest, and overall enhancement in
physical strength. Eugene Shippen, and William Fryer, in their book “The
Testosterone Syndrome,” relate diminishing sexual interest to a sign of future
heart disease and diabetes, conditions common in the male menopause (“The
Testosterone Syndrome,” pp. 59)
At the end of this research, I would like to notice
and bring example of the fact that majority of scientific world hold opinion
that artificial testosterone if correctly applied can bring much of good to the
human kind, especially to elderly.
“Standford R. is seventy-four years old now, but he
has had heart problems since the early 1970s. It did not make life easy for
him. He is an athletic man who likes to hunt, 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. The chest pains started up again in
a few years later. His chest pains went away, his energy returned and when he
is not walking over the hills and fields and hunting in the woods, Standford
makes love. Sometimes twice a day (“The Testosterone syndrome,” pp79).
As can be concluded from all researches discussed
above change in testosterone level triggers changes in behavioral pattern, and
environmental change followed by change in behavioral pattern triggers change
in testosterone level.
The arguments in scientific world regarding
testosterone and their role in human anatomy are not over yet. The subject is
hard to explore, because experiments that has to be done in order to find right
answers are not considered to be ethical on humans. The scientific world has
no choice, but to use random historical facts to come to the answers. However,
the fact the testosterone play a huge role in human development and behavior is
not argued by any more.
“The Testosterone Syndrome”; Eugene Shippen, M.D. and William Fryer, M.
Evans and Company, Inc., 1998
“The Trouble with Testosterone and other essays on the biology of the
human predicament”; Robert M. Sapolsky, Scribner, 1997
“The Hormone of Desire; The Truth about sexuality, menopause, and
testosterone”; Susan Rako, M.D., Harmony Books, 1996
“Never Too Buff”; John Cloud
“The He Hormone”; Andrew Sullivan