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Biological Differences Between Men and Women

What are some of the biological differences between the male and female bodies?

What are some of the biological differences between the male and female bodies?

Biological Differences Between Males and Females

We all know that male and female humans are anatomically different. Furthermore, the male and female bodies behave differently when it comes to the manifestations and treatments of various diseases. These differences are due to biological and genetic reasons. Upon closer examination, the presence of several hormones and other chemicals, especially the quantity of the two major ones present in both sexes—androgens and estrogens—account for the difference.

Differentiating Gender and Sex

In recent years, there has been a push from doctors, health organizations, and the queer community to define and differentiate between sex and gender (and with that, gender identity).

According to the Planned Parenthood website, sex is assigned at birth by a doctor (either male or female), whereas gender is assigned by social and legal statuses largely informed by mainstream society's ideas of male and female behaviors, characteristics, and thoughts. Gender identity is how one personally feels and chooses to express themself.

This article will focus on the differences between the two sexes—biological differences between the male and female bodies. We'll discuss how hormones and other chemicals affect fertility, secondary sex characteristics, genetics, and other non-sexual functions. The following definitions of a biological woman and man are taken from Planned Parenthood's page for Sex and Gender Identity resources.

Biological Woman

"A person with XX chromosomes usually has female sex and reproductive organs, and is therefore usually assigned biologically female."

Biological Man

"A person with XY chromosomes usually has male sex and reproductive organs, and is therefore usually assigned biologically male."

Biological Differences in Fertility

Fertility is one of the major differences between men and women. On one hand, men are continuously fertile beginning at puberty to almost 100 years of age (though by that time they are physically unable to engage in sexual activities). Until very late in life, sperm is still viable though of poorer quality.

Men are fertile for this long because there is a continuous production of sperm through the process called spermatogenesis. The process begins with germ cells which are essentially immortal. The cells are haploid since they have only half the number of chromosomes, which, in this case, is 23. In males, all of these cells are not used at once during the reproductive process. Only some will become mature germ cells to compete in the arduous task of uniting with a female germ cell—an ovum.

On the other hand, women are fertile for roughly 12 hours each month from menarche (their first menstruation) up until their fifties when menopause begins for most women. Fertility for them is limited because they have a set number of eggs. During fetal development, there are initially three million to four million follicles or eggs present, but through the process of apoptosis (cell death), that number drops to about just around one million eggs by the time of birth. This cell depletion will continue throughout the female's life.

By menarche, there are only 500 thousand eggs available to continue this monthly cycle for the next five decades until menopause is reached. In about 50 years, a woman releases about seven thousand eggs and only one in 12 is available for fertilization. The approximately 493 thousand remaining eggs never released for fertilization go to waste.

A More Complicated Process for Women

Even though the fertility process for men and women is basically hormone-driven and both begin with the release of a hormone from the hypothalamus, the fertility process is a little more complicated for women. It involves several critical steps with other hormones to progress from the beginning to the end of the menstrual cycle. These steps are as follows:

  • The release of the gonadotropin releasing hormone from the hypothalamus causes an increase in follicle-stimulating hormone (FSH). This is the beginning of the menstrual cycle.
  • Ten to 12 ovarian follicles ripen due to the increase in FSH level.
  • One of the follicles becomes the dominant one, causing an increase in estrogen levels.
  • The gonadotropin releasing hormone level rises more, causing an increase in luteinizing hormone and FSH levels and thus triggering ovulation. This is the midpoint in the menstrual cycle.
  • After the egg is released, the dominant follicle becomes what is called a corpus luteum. The corpus luteum will be active for two weeks and secretes estrogen and progesterone. Both of these hormones get the uterus ready to receive a fertilized egg.
  • If the egg is not fertilized during the 12 hour window specifically within the two week period, the corpus luteum degenerates, and estrogen and progesterone levels drop. This drop in the hormone level starts the menstrual period and thus ends the menstrual cycle.

Quanitity of Hormones Determines Differences in Secondary Sex Characteristics

The obvious physical differences between the sexes are influenced by the number of androgens and estrogens, two chemicals from the steroid family of chemicals that are released into our bloodstream. The biggest differences occur during the development of our secondary sex characteristics which begins at puberty. We know what they generally are and I will not go into any details about them here.

All the sex hormones in men and women originate from acetate and cholesterol molecules present in their bloodstream. The estrogens present in both sexes, more so in women than in men, are produced from the chemical breakdown of testosterone which is also present in the blood of both sexes. In case you didn't know, testosterone is produced in both the testes and ovaries. This is because the testes in the human male were ovaries during fetal development until a chemical in the male body triggered the sequence to cause them to descend to the lower level into the scrotum and thus become testes.

The testes make about seven milligrams of testosterone a day and 1.75 milligrams of that is converted to small amounts of estradiol present in the blood of men. On the other hand, the ovaries in women only make about 0.3 mg of testosterone and a little more than 0.15 mg of that is converted to estradiol.

As we can see here, it is the ratio of testosterone to estradiol and the potency of the two hormones that accounts for the big differences between the sexes. Estrogens are a thousand times more potent than testosterone. The ratio of the amount of testosterone to estradiol found in men is three to one, while the ratio of these two hormones in women is one to one.

Men also make about 20 times more testosterone than women, though the amount of testosterone converted to estrogens in women is 200 times more than in men. It doesn't take much of either of these hormones to change the physical appearance of each sex to its opposite appearance.

The Non-Sexual Functions of the Sex Hormones

Sex hormones not only exert their effects on the reproductive organs but also affect the physiological functions of non-reproductive tissues as well. These tissues are generally called somatic cells as they essentially make up the rest of the tissues in the body ("soma" is the Latin word for "body"), such as the muscles, eyes, bones, etc.

Teenage Growth Spurts

Estrogen plays a critical role in our growth rate during puberty, controlling the growth of the cartilage and bone tissues. Rapid growth spurts generally occur in girls earlier than in boys once puberty is reached due to the higher level of estrogen in the female body. This is why girls are taller than boys in the first year or so as teens and why boys catch up later in height.

Cardiovascular Health and Osteoporosis

Estrogen also has a strong influence on the cardiovascular system. Estrogen decreases the incidence of heart attacks, kidney diseases, and other cardiovascular ailments in women since they have more of it than men. However, that benefit in women disappears once they reach menopause since estrogen levels drop and their testosterone levels go up.

A decrease in estrogen levels in both sexes causes an increase in the incidence of osteoporosis (bone loss) since estrogen controls the rate of bone loss and the resorption of calcium to produce bone tissue. When estrogen levels drop, the rate of bone loss is greater than the rate of bone resorption. The problem is worse in women since their bones are generally less dense than in men.

Normal chromosomes of a human. Note the XX chromosomes for female and the XY chromosomes for male. The male Y chromosome is much smaller than the X chromosome that it is paired with.

Normal chromosomes of a human. Note the XX chromosomes for female and the XY chromosomes for male. The male Y chromosome is much smaller than the X chromosome that it is paired with.

Genetic Differences Between Men and Women

If you were to look at chromosome pair 23, XX for female and XY for male, the differences between the sexes are apparent. The "Y chromosome" is much shorter than its corresponding "X chromosome."

Determining Maleness

Despite its size, the "Y chromosome" carries two of the most important genes for a male. One of these genes is called SRY which determines the maleness of the human species. This is the gene that triggers the sexless gonads to become testes in the male; otherwise, they stay up in the abdomen to become ovaries for the female. In other words, it is chromosome pair 23 from the male that determines what sex the developing embryo will ultimately become after conception. The other gene controls the production of sperm.

Mitochondrial Inheritance

The other genetic difference between the sexes is the inheritance of mitochondrial DNA in the female. Mitochondria are present in all the cells of both sexes but are passed from one generation to the next exclusively through the mother. The genes they carry are replicated and do not go through any recombination as the rest of the genes do during fertilization. Maternity testing is based on this knowledge of mitochondrial DNA properties. Paternity testing is generally performed using the nuclear DNA present in all non-reproductive or somatic cells.

Differences between male and female bodies ranges from the physical to the genetic.

Differences between male and female bodies ranges from the physical to the genetic.

The Quantity of Hormones Matters Most

The above information clearly shows that the physiological differences in the sexes are biological as well as chemical driven. It is the quantity of testosterone and estrogen in the blood of both sexes, as well as the ratio of the two hormones present, that affects the physiological activities in both sexes as well as the physical attributes of the male and female human body.

Sources

© 2011 Melvin Porter

Comments

eyerus on December 06, 2017:

I like the article I do not know women are fertile only 12 hours is for all women why I ask that are when I become pregnant my second child I was not in 12 hours fertile time its before 24 hours so can brief me a little with my situation

Michaela from USA on February 29, 2016:

How do you account for chromosome formations that are outside of the XX and XY standard? Because new scientific study has found that it's very common for strands such as XYX and XXX to exist, which really throws into question just how binary biological sex really is.

Melvin Porter (author) from New Jersey, USA on February 09, 2013:

Savvydating, thanks for your comment. Testosterone level goes up in women when they reach menopause. This the reason why some women begin to see an increase in hair growth in certain areas of their body such as under their chins or above their upper lips.

savvydating on February 09, 2013:

I didn't realize that testosterone levels go up in women after menopause. Good to know...yet, the sex drive goes down even though T is up. I guess it's about balance?? Don't quite know. I'm no scientist...at any rate, I very much enjoyed your hub.

Melvin Porter (author) from New Jersey, USA on December 29, 2011:

Pandoras Box, you are probably right because all the testosterone present in both male and female comes from the enzymatic breakdown of progesterone and estradiol present in the body of both sexes. Testosterone does not play much of a role until its level goes up during puberty in boys to produce the well known secondary sex characteristics of the male and turn on the growth spurt later in the teen years. Before puberty the physical characteristics of the body of boys and girls are essentially the same with the exception of the reproductive system, since estrogen plays more of a role in the body before puberty. However, testosterone does affect the behavior of boys to a greater extent than girls even though the female body is more sensitive to testosterone than the male. The rest is genetically controlled.

Pandoras Box from A Seemingly Chaotic World on December 29, 2011:

It's been a long time since I looked at it, but the way I recall it was that the mother's body provided the developing fetus with the testosterone, and that the levels varied quite widely, allowing for the theory that it is this variance which may affect the sexual preferences of the baby, when it gets a bit older, at least. The gene theory is flawed due to lack of hereditary evidence. The embryonic testosterone theory is totally random, or was the last time I looked at it. No, wait, lol... I think there was some evidence that it could be often lower levels in later pregnancies. Anyway, too much testosterone but not enough to cause physical differences could -the theory went- cause a female fetus to develop lesbian preferences and male tendencies, without the physiological characteristics. Not quite enough in a male embryo could randomly turn out in male physiology without the male tendencies, and with homosexual preferences. The theory nicely explained everything, children's early self-identification as gay, the lack of a gene or any hereditary evidence, as well as physiological abnormalities, if I recall right. And it did contain a totally random quality, if not technically completely random. But I do guess nothing ever came of it, since I haven't heard anything of it in a long time. Not high on my agenda these days, but if I get a chance to look it up I'll let you know if I find anything.

Melvin Porter (author) from New Jersey, USA on December 29, 2011:

Pandoras Box, thanks for your comment on my hub. There is also some evidence that the level of testosterone is high during embryonic development. This high level appears to affect the wiring of the brain in the male embryo to engender physiological activities geared toward being a male.

Pandoras Box from A Seemingly Chaotic World on December 28, 2011:

Interesting hub. There's a theory out there that it is natural variations in embryonic testosterone levels which gives us our very broad range of sexualities.