Learn About Sexuality

Human sexual anatomy and development

Sexuality is about appreciating the human body and sexual anatomy. We need to understand the function of the male and female genitalia as well as the changes that occur throughout our lives. We can also benefit from knowing what stimulation may be pleasurable or lead to orgasm.

The reason we have genitals is because our species has two sexes: male and female. Most plants and animals reproduce sexually (two parents). Way back in our evolutionary history, our forebears would have been much simpler single-sex organisms. There was no need for two sexes or genitals.

The step of evolving from a one-sex being into a two-sex being was inevitable because of the huge advantage that sex provides. The many more combinations possible by combining gene pools from two parents means that the organism can evolve more quickly. Evolution occurs as a result of the random selection of the millions of genes we inherit from our parents. Some combinations are successful and some are not. Those individuals with a more advantageous combination of genes are able to reproduce and survive more successfully than those who are less advantaged.

During this transitionary time (while a one-sex organism was evolving into a two-sex organism) all individuals must at least potentially have the anatomy of both sexes. So the single-sex organism evolves a rudimentary ‘phallus’. Those individuals who are most successful in penetrating and fertilising another individual (very gradually) ensure that their offspring may include more proactive males. Those individuals who are more passive and willing to be impregnated evolve into females. We still have the remains of this duality (both male and female) in our genes today.

There are few anatomical differences between the sexes. Sometimes we have only one of something. We have one head, one brain and one sex organ. Other times we have two of something for backup purposes. We have two arms, two legs, ovaries and testes. Sex is only a minor detail in anatomical terms. There are a few key differences. A man has nipples but he does not develop the mammary glands that form the female breast.

Our internal reproductive anatomy originates from different embryonic structures and is an ‘either or’ option. Our genes determine whether we develop testes or ovaries. Thereafter the development of our internal reproductive anatomy depends on the hormones produced by the testes (or not in the case of the female). We end up with one set: either male or female. There is some symmetry even so.

The testes or ovaries, produce our genetic material (sperm or egg). Both are connected via tubes that allow the sperm and the egg to meet in the woman’s uterus. Intercourse is an activity that facilitates ejaculation. The penis and the vagina together act as reproductive conduits. When a man ejaculates his sperm (from the testes) pass from the man’s penis (via the vagina) into the woman’s uterus to meet the egg (produced by the ovaries).

Miscarriages are where a pregnant woman loses the child she is carrying in her womb (uterus). Miscarriages can occur at any time during a pregnancy. Either the zygote does not attach properly to the uterus wall or the placenta becomes detached. Miscarriages are more upsetting the later they occur in pregnancy. Sometimes the zygote does not develop. The woman may still have all the symptoms of pregnancy. She has to have the zygote removed from her uterus wall before her body returns to normal.

The sex organ originates from the same structures in the embryo. It is only the degree of development that differs. The hormones sent out by the testes ensure that the genital tubercle undergoes significantly more development in a boy. Unlike the internal reproductive anatomy, this is not an either or option. We have a sex organ regardless of which sex we are. Even though the clitoris does not function as a phallus that is capable of penetrating and impregnating another person. The clitoris is the source of female orgasm.

At puberty men develop an Adam’s apple and the pitch of their voice lowers and deepens. Men’s shoulders are wider than women’s and their buttocks are smaller and rounder. Women have larger and wider hips than men. Their buttocks are larger and elongated. Girls and boys have equal amounts of androgens until age 7 or 8. During adolescence the levels of androgens rise markedly in boys but less so in girls. Women have around two thirds of men’s levels of androgens. Pre-adolescent boys and girls have equal amounts of estrogens. During adolescence estrogens increase abruptly in girls but there is only a slight increase in boy’s levels. Women have much higher levels of estrogens than men have. These hormone changes do not correlate to the steep increase in male responsiveness at adolescence and the much slower increase in female responsiveness.

… the reported levels of the 17-ketosteroids in the human male differ from the reported levels of the 17-ketosteroids in the human female in a manner which more or less parallels the differences which we have found between the median frequencies of orgasm at various ages in the two sexes. (Alfred Kinsey 1953)

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