The 7 Sexes: Biology of Sex Determination

2. Wild Guesses in an Era of Scientific Ignorance

2 Wild Guesses in an Era of Scientific Ignorance Almost all of the topics taught in K–12 or undergraduate introductory science courses come from work published in the last two centuries. Before the nineteenth century, very little of the chemistry, biology, geology , astronomy, or physics (other than Newtonian) that is covered in a twenty-first century class had been discovered. Almost all of a medical school curriculum, with the exception of gross anatomy, is a product of work done in the past two centuries. However, humanity centuries ago had the same curiosity about life and the universe as those born today. One of the universally recognized experiences of all people born is that roughlyhalfaremalesandabouthalfarefemales.Whenitcomestoclassifying who is a male and who is a female at birth, almost every adult in the world will use the external genitals. In a male there are a penis and a scrotum containing two testes. In a female there is a vaginal passageway surrounded by labia and a clitoris. Except for rare occasions we do not see the genitalia of our fellow adult human beings. Usually we classify a person as male or female by characteristics such as body shape, the presence or absence of hair on the face, the length, distribution, and style of hair from the cranial part of the head, the bony structure of the limbs and face, the deepness or higher pitch of voice, the presence or absence of enlarged breasts, and the presence or absence of an “Adam’s apple.” To that, in most cultures, we add the clothing that people wear and the behavior we assign to males or females out of tradition or experience. For most people humanity falls into two categories: half are male andhalfarefemale.Theremaybeculturalreasonswhyamaleorafemale baby is preferred, but even in cultures in which there is no such cultural Wild Guesses in an Era of Scientific Ignorance 7 bias, prospective parents and family members are curious about the sex of the child before it is born, and virtually every period of history has left cultural evidence behind that it believed it could either predict the sex of a baby or actually manipulate it to a desired sex before it is born. The oldest document recording such beliefs is the Berlin Papyrus, which was written about 1400–1600 bce (i.e., some 3500 years ago).1 The authorclaimsthatiftwopotsaresetupwithamixtureofsandanddates, and if urine is added from a pregnant woman to both pots, and if seeds of barley are placed in one pot and seeds of wheat in the other, then the child will be a boy if the wheat sprouts first and a girl if the barley sprouts first. Some current folk beliefs have not varied since antiquity. Many in Appalachian regions of the United States still believe that a male who loses a testicle will be capable of producing only one sex of children. Some folk beliefs claimed that males come from the right testis and females from the left testis. A variant of that is that males come from the embryo implanted on the right side of the uterus, females from embryos implantedontheleftside.Furthervariationsonthesethemestakebreast size into account. Some believe that if the right breast swells larger than the left breast the baby will be a boy. There is no reason given why this should be so. A more rational argument claims that young or very old males are more likely to have daughters, while males in their prime are likely to have sons. This reflects a belief that males are more active or aggressive than females, and assumes the fate of the sperm is determined by the behavior of the male. Similar logic leads to the belief in many cultures that women who are pregnant experience more active movement if it is a boy than if it is a girl. A similar active/inactive principle is at work in thefolkbeliefthatapregnantwomanwhobathesincolderwater(orwho is exposed to cold water by rain) is more likely to have a daughter. Here hot/cold are related to the male as hotter (sweats more) than the female. Some cultures used astronomical signs. In Assyrian culture, a halo aroundthemoonindicatedatimetocopulateifthecoupledesiredason. Among ancient Hindus if a woman had excess menstrual flows she was prone to producing daughters. Some folk myths were based on diet. For example, eating a rooster’s testes after intercourse would assure birth of a son, as would eating more meat, especially red meat. More recent folk 8 myths in North...