Evolution and Gynaecology

  Dr. Law Chi Lim *

Ever since Darwin published his The Origin of Species in 1859 and formalised the evolution theory, it had been the subject of wide spread controversies. Today, most of us have been brought up to believe that evolution plays a major part in the origin and development of various life forms on earth. Since the continuation of life depends on reproduction, it is not surprising that evolution theory can be used to explain some of the clinical problems that we encounter in the practice of Obstetrics and Gynaecology.

Morning Sickness

Most pregnant women suffer from some degree of nausea and vomiting, especially during the first three months. Its severity may vary from just a little loss in appetite to severe cases of hyperemesis gravidarum. Most are resigned to accepting it and their doctors usually react to a complain of morning sickness with a shrug, or a pat on the shoulder and may be a prescription for antiemetics which make the women so drowsy that they forget about their nausea.

It is strange, however, that "woman kind" should evolve to develop such a strait during pregnancy. Surely, a pregnant woman who has a healthy appetite during pregnancy (and thus able to provide more nutrition to the embryo) must have some advantage over her peers who have morning sickness. Then why have pregnant women retained this problem during evolution?

It was in the late 1980s when biologists, such as Margie Profet of the University of California at Berkeley, first offered an explanation. Morning sickness, she said, could be an evolutionary adaptation, one that could protect a vulnerable fetus from natural toxins. When Homo sapiens emerged on earth between 100,000 and 200,000 years ago, they mainly lived as hunter- gatherers. With their limited tools, life was hard and food could be scarce and they often had to make do with any kind of food they could find. A pregnant woman with a voracious appetite would be at risk of ingesting various kinds of toxins or parasites (like Toxoplasma) which might be harmful to the embryo. By avoiding certain foods during pregnancy (particularly during the first few months when the fetus was most vulnerable), women might improve their chances of having healthy children-and so pass on the same aversion to future generations.

One recent study (ref 1), which looked at the results of 56 morning sickness studies covering 79,000 pregnancies in 16 countries, indicated that the most likely types of food to cause morning sickness in meat eating cultures were meat, fish, poultry and eggs. This can be explained by the fact that, in the days before refrigeration was invented, meat was the food most likely to carry parasites and pathogens that could harm a fetus, as well as putting the mother at risk.

Thus, the term " morning sickness" is a misnomer. It is not really a sickness but a mechanism to protect mother and fetus. As a corollary, human female must also have evolved a kind of compensatory metabolic mechanism so that the developing embryo is able to extract enough nutrition from the mother even though the mother herself may be suffering from relative malnutrition during the days of severe vomiting. Those who do not will not be able to propagate their genes. Perhaps if we explain "morning sickness" in this light to those pregnant women who suffer from distressing symptoms, it may bring them a little comfort and help them to accept their plight.

Spontaneous Miscarriages

We now know that the majority (up to 78%) of fertilised human eggs are never implanted. Even after implantation, may be up to 50 percent of them end up in abortion. Given such an inefficient reproduction process, how the human race could have ever spread across this earth?

The answer lies in the fact that by eliminating faulty conceptus early in the process, the mother saved time and energy before embarking on another attempt in reproduction. In order to do that, the mother must have a biological mechanism to detect embryos which are defective. Women who are unable to do that will carry abnormal fetus to term and are quickly wiped out by evolution.

One often-asked question by a woman who experiences the trauma of spontaneous abortion is: Why me? Why does everybody else seem to be able to carry his or her fetus to term? An understanding of the evolutionary significance of the process of spontaneous abortion may help the woman to accept this unhappy chapter in her life.

Another question often asked is how soon can a woman get pregnant again after a spontaneous abortion? The standard answer of one to two months afterwards is often met with skepticism. She may become more credulous if she is made to understand that if the human body had been so designed that it took a year or two for a woman to recover before getting pregnant again, the human race would never have become a dominant force on this planet.

Fetus, the aggressor

According to evolution theories, life is selected on the principle of survival of the fittest. A baby will have more chance of survival if it is able to extract more nutrients from the mother. Thus Human Placental Lactogen (HPL) ties up maternal insulin so that her blood glucose level rises to provide more sugar for the fetus. When this tug-of-war between the mother and fetus gets out of hand, the mother develops gestational diabetes. Likewise, a fetus that detects a risk of growth retardation will secret substances to constrict the mother's peripheral blood vessels to divert more blood to the placenta. Thus a moderate rise in maternal blood pressure is actually associated with a bigger baby and lower mortality.

Postpartum sexual problems

Postpartum sexual problems are very common. In one study (Ref 2) of postpartum women, only 17% reported not experiencing any sexual problem three months after delivery. Sexual problems included dyspareunia, loss of sexual desire, problems with orgasm, etc. Dyspareunia is significantly associated with breastfeeding. This is due to the hormonal changes during lactation resulting in vaginal dryness and loss of libido. Such changes do indeed have evolutionary advantage. A woman who is lactating and caring for her young should really not get sexually aroused (and thus possibly get pregnant) too soon if baby is to receive maximum care and attention. If the husbands can be made to understand that, perhaps some of the marital disharmony associated with postpartum sexual problems between couples can be more readily resolved.

Cancers of the female genital tract

Cancers of the female genital tract is often associated with a high number of menstrual cycles that women have during their lifetime. The modern woman with early menarche, late menopause and infertility is at high risk of such cancers. In contrast, a Stone-Age woman with relative malnutrition, late menarche, repeated pregnancies and prolonged periods of lactation, must have had three to four times less the number of menstrual cycles than her modern counterpart. Coupled with a much shorter life span then, cancer of the uterus and ovaries must be virtually unknown in those days. Nevertheless, modern man is well known for being able to manipulate his environment and thus able to succeed on earth. The invention of modern oral contraceptives, apart from sexual liberation of the female, had unintentionally (but rather expectedly for students of the evolution theories) decreased the incidence of cancer of the ovaries and uterus by up to 40 % in long term users.

Why does man (and most male animals) wants sex that much?

As mentioned earlier, human reproduction is very inefficient, but it ensures that new offsprings are cared for properly. In contrast, asexual reproduction is far more efficient. Imagine that, in the beginning of time, God had somehow forgotten all about Adam, and Eve had been created alone and had been able to reproduce herself asexually. Her progeny would have spread like wildfire. Some people would contend that with only the gentle sex ruling the earth, the world would be a much more harmonious place to live in. No more human suffering like falling in and out of love, no more wars like the Trojan War or the those waged by various Chinese emperors through the ages as a result of spells cast by various famous women.

Alas, apart from the disadvantage of being unable to experience love and sex between men and women, the human race, which would then have been genetically homogenous, would have been very vulnerable to pathogens. A particularly virulent influenza virus would have wiped out the entire human race in one winter.

The success of any living organism depends very much on its ability of mutation to adapt to its environment. The modern cheetah is an endangered species at the verge of extinction. Their number is now so small that the gene pool is getting smaller and smaller, which makes them very susceptible to diseases. One day, its entire population may be wiped out by some particularly severe infectious disease.

Why do man want sex and woman often don't?

In many animals, ovulation is heavily advertised. This may be in the form of red and swollen genitalia like the monkeys, the smell of a female dog in heat, or the cries of a receptive female cat on the roof in the middle of the night. In contrast, the human male has no idea when a woman is ovulating just by looking at her or smelling her (particularly when Christine Dior has given her a perfect camouflage). The human male has therefore evolved to want to have sex with a woman as many times as possible during the month to increase the chance of pregnancy.

On the other hand, the human female does have some idea when she ovulates. If she had an insatiable sexual appetite all the time, she would not be able to tell which male in her clan is the father of the child she would be carrying. On the other hand, if she selectively has sex with the man she wants and is able to show him that he is the father of the baby, she will have a much higher chance of the male's subsequent assistance in terms of protection and provision of food for her and her young. No wonder chastity is revered in most cultures.

Conclusion

If readers find this article provocative, it is because it is meant to be so. Not everyone will agree with the view points and speculations expressed here. Indeed, how man interacts with his environment will always be a rich source of debate and speculation. It is also the purpose of this article to probe readers into contemplating the relationship between our past and our present. At the same time, we need to know how our past has shaped us before we are able to consider what the future will bring.

References

1. Morning Sickness: A Mechanism for Protecting Mother and Embryo, Sam M Taxman and Paul W Sherman, The Quarterly Review of Biology, June 2000, Vol. 75, and No. 2.
2. Women's sexual health after childbirth , G Barrett et al , British Journal of Obstetrics and Gynaecology Feb.,2000 , Vol. 107 No.2

* Dr. Law Chi Lim is a Fellow of the College of Obstetricians and Gynaecologists.