Life is Sex (Part III)

How does male sexual function contribute to new human life?

Once the sexual organs have matured so the male can produce sperm and the female can release an egg what is needed for new human life is to join them together to form a zygote (fertilization). The natural way human reproduction takes place is by the male and female coming together in sexual intercourse. This intimate physical union requires the man to insert his erect penis deep into the vagina of the woman and release semen (with enough healthy sperm) near the cervical opening of her uterus. The sperm can then swim up through her uterus to try to fertilize the egg.

Fertility in the male refers to him being able to produce enough healthy sperm to bring about fertilization and new human life. This is done by the man’s testes. It requires him to have enough Follicle-Stimulating Hormone (FSH), Luteinizing Hormone (LH) and their respective receptors on specific cells in his testes. These hormones tell his testes to produce testosterone and sperm. The sperm is put in nutrient fluids from his seminal vesicles and prostate gland to form semen. As noted above, during sexual intercourse semen is released from the erect penis deep in the woman’s vagina to put the sperm where they need to be to have a chance for new human life. 

The normal amount of semen usually needed for adequate fertility is at least 2 milliliters and should have more than 20 million per milliliter. Their appearance (morphology) and ability to move well enough (motility) are very important factors that affect fertility. If most of the sperm look abnormal and/or are unable to swim vigorously then fertilization is unlikely to take place.

Experience teaches that just because the male has the right parts and has undergone puberty doesn't mean he will be fertile. There are several reasons why a man may not have enough healthy sperm resulting in male infertility. These include emotional stress, smoking, use of alcohol, sexually transmitted infections, vitamin and mineral deficiencies, radiation, trauma, diabetes, thyroid disease, aging and obesity. Also, because sperm production requires a lower temperature the testes are housed in the scrotum away from the body. Overheating of the testes due to frequenting saunas or wearing tight underwear can also result in male infertility.

Potency is being able to deposit the sperm deep inside the vagina of the female. This means having a firm enough erection to penetrate deep into the vagina and being able to ejaculate semen. It depends on him having a normal penis and normal nerve and vascular function.

An erection is achieved by hydraulic pressure. Running the length of the penis (above and on each side of the urethra) are the corpus spongiosa and the corpus cavernosa. These tube-shaped venous chambers are surrounded by strong fibrous tissue. Sex-related thoughts and stimulation of the penis and pelvic region activates the autonomic nerves which send out a neurohormone called acetylcholine. It attaches to specific receptors on the blood vessels in the penis. This causes an increase of arterial blood flow into these chambers and a reduction of venous blood flow out of them. The final result is the collection of blood within these chambers and erection. 

After erection, with continued stimulation the autonomic nervous system sends out a different neurohormone called norepinephrine. It attaches to specific receptors in the pelvic region which causes coordinated contraction and ejaculation of semen. This is usually accompanied by the pleasurable sensation of orgasm. Soon after this happens the autonomic nervous system turns off its acetylcholine and the penis loses its erection and becomes flaccid.

As noted above, adequate penile erection resulting in ejaculation is a well coordinated process that involves having adequate pelvic blood flow and nerve function. If there are significant problems, then erectile dysfunction, or impotence, is the result.  In other words, even if the male is making enough semen with enough healthy and active sperm, if he can't deliver them where they need to go this will result in male infertility as well. 

Fatigue and emotional causes of erectile dysfunction are usually temporary, but there are many conditions that can lead to permanent impotence. Atherosclerosis (hardening of the arteries), usually related to smoking, hypertension, diabetes and hyperlipidemia, can cause peripheral vascular disease and limit blood flow to the penis. Moreover other conditions associated with vascular problems like coronary artery disease, congestive heart failure and kidney disease can all lead to impotence as well. In particular, diabetes not only affects blood flow but also nerve function and therefore diabetic men are particularly at risk for impotence.

Finally, although most of the conditions that lead to impotence and male infertility are related to vascular and/or nerve dysfunction, there is one that is related to a defect in the structure of the penis. Peyronie’s disease is a condition in which scar tissue forms within the walls of the penis resulting in a deformed and often painful erection. This usually makes sexual intercourse not only very uncomfortable but often physically impossible. 

One can see that everything has to be just right for the male to produce enough semen with enough healthy sperm and place it deep inside the female’s uterus for fertilization to be possible.

Three Questions for Mr. Darwin

    1. Where did the information come from to tell the male testes to make enough sperm?

    2. Where did the parts and mechanism come from to make the penis erect?

    3. How did the male develop the ability to ejaculate semen?


Also see Dr. Glicksman's Series on

"Beyond Irreducible Complexity"

"Exercise Your Wonder"


Howard Glicksman M. D. graduated from the University of Toronto in 1978. He practiced primary care medicine for almost 25 yrs in Oakville, Ontario and Spring Hill, Florida. He now practices palliative medicine for a Hospice organization in his community. He has a special interest in how the ethos of our culture has been influenced by modern science’s understanding and promotion of what it means to be a human being.

Comments and questions are welcome.

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