Humans have tried to choose the sex of their offspring before birth for thousands of years, and we have historically employed all sorts of superstitious, misinformed, injurious, and downright silly methods of doing so. Reasons for favoring one sex over another could be financial (in cultures where women may not inherit property or other assets), social (in cultures where men are valued more highly than women), arbitrary preference, or “family balancing,” where a family wishes to have a mix of both boys and girls.
Superstitions and folklore about sex selection tend to catch on and propagate because, by definition, any sex selection method – no matter how bunk it is – will work around 50% of the time. If a couple uses a method to choose the sex of two children, there’s a 25% chance that they’ll get the desired sex both times in a row, and for three children, there’s a 12.5% chance that they’ll get the desired sex each time. Since most modern couples have between one and three children, a fairly significant proportion of these families will experience a one-hundred percent success rate when employing a method to choose the sexes of their children. This purely-by-chance success tends to create an illusion of efficacy. Unfortunately, these methods are circulated further because they are myths that people very much want to believe.
Some of the earliest documented sex selection theories grew out of Aristotle’s theorizing of women as “incomplete” or “defective” versions of men. The ancient Romans and Greeks believed that female children were the product of an “alteration in the course of nature” during conception, where the seed of the man’s right side was cast to the woman’s left side or vice-versa (where right-side sperm into a right-side ovary, which was considered the “natural” course of conception, would result in a boy). Aristotle’s theories influenced many Western thinkers throughout the following centuries and still provide the basis for much Western philosophy and values today.
An 18th century French text called The Art of Boys proposed that a man’s right testicle and a woman’s right ovary contain the material to generate boys, and a man’s left testicle and a woman’s left ovary contain the material to generate girls. The text suggested that the removal of the left testicle or left ovary would result in the birth of boys. Needless to say, this theory resulted in needless pain and discomfort, not to mention disappointment, among those who practiced it.
Not all sex selection methods were quite so damaging. Other theories proposed that astrological signs and timing of intercourse depending on the alignment of stars determined the sex of a baby. This 13th-century Chinese conception chart was designed to predict the sex of a baby before birth depending on the age of the mother and the month of conception.
Other theories advocated particular preparation of certain animal parts to conceive a boy. The Italian physician Trotula wrote in 1059:
“If they wish to have a male child let the man take the womb and vulva of a hare and have it dried and pulverized; blend it with wine and let him drink it. Let the woman do the same with the testicles of the hare and let her be with her husband at the end of her menstrual period and she will conceive a male.”
Our modern sex selection theories aren’t quite so unappetizing, but unfortunately, there’s no good scientific evidence that you’re any better off using them than pulverizing hares or consulting astrological charts. The Shettles Method purports that the timing of intercourse in relation to ovulation will determine the sex of a baby, with intercourse no more than 12 hours before ovulation resulting in a boy, and intercourse two to three days before ovulation resulting in a girl. While Dr. Shettles claims his method has a success rate of 80-85% for boys and 75-80% for girls, numerous scientific studies (such as this one, this one, and this one) investigating the theory have not found a significant effect.
If this news disappoints you, you’re not alone – hoping for one gender over the other is common and nothing to be ashamed of. However, despite anecdotal evidence, natural methods of gender selection without the use of artificial procedures don't have the empirical results to support their claims. It’s tempting to believe what we’d like to believe, and the Shettles Method won’t harm you if you choose to try it anyway (as long as you and your partner don’t have fertility problems and you’re willing to abstain or use condoms during the required periods), but try not to get overly invested in having one sex over the other – the evidence suggests you have a 50% chance of setting yourself up for disappointment.