Sex Selection - History and Folk Beliefs

History and Folk Beliefs

There are a wide variety of social sex selections methods which have not been demonstrated to be effective. Because even implausible and ineffective methods have a "success" rate of 50%, many continued to be recommended by word of mouth.

The Greeks and Romans did not have a consistent theory of how sex was determined. Pliny the Elder claims that tying the right testicle of a ram will cause him to produce only females, but does not claim this about other creatures. Pseudo-Plutarch lists many Greek theories of sex determination, including heat and cold, left and right testicles, left and right sides of the body, sperm crossing or not crossing from one side of the womb to the other, and the strength or dominance of various body parts.

Some people believe that timing conception according to astrological charts can influence a baby's sex, though there is no evidence to support this or any other timing method. A 13th century Chinese conception chart purports to be able to identify the sex of the baby before birth.

An 18th century French book called The art of boys suggested an extreme method of ensuring children of one sex. The author suggests that one testicle and one ovary are intended for each sex. By removing a testicle or ovary, children of the other sex can be guaranteed.

Sperm sorting utilizes the technique of flow cytometry to analyze and 'sort' spermatozoa. During the early to mid 1980s, Dr. Glenn Spaulding was the first to sort viable whole human and animal spermatozoa using a flow cytometer, and utilized the sorted motile rabbit sperm for artificial insemination. Subsequently, the first patent application disclosing the method to sort "two viable subpopulations enriched for x- or y- sperm" was filed in April 1987 as US Application Serial Number 35,986 and later became part of US Patent 5,021,244; and the patent included the discovery of haploid expression (sex-associated membrane proteins, or SAM proteins) and the development of monoclonal antibodies to those proteins. Additional applications and methods were added, including antibodies, from 1987 through 1997. At the time of the patent filing, both Lawrence Livermore National Laboratories and the USDA were only sorting fixed sperm nuclei, after the Application Serial Number 35,986 patent filing a new technique was utilized by the USDA where "sperm were briefly sonicated to remove tails". USDA in conjunction with Lawrence Livermore National Laboratories, 'Beltsfield Sperm Sexing Technology' relies on the DNA difference between the X- and Y- chromosomes. Prior to flow cytometric sorting, semen is labeled with a fluorescent dye called Hoechst 33342 which binds to the DNA of each spermatozoon. As the X chromosome is larger (i.e. has more DNA) than the Y chromosome, the "female" (X-chromosome bearing) spermatozoa will absorb a greater amount of dye than its male (Y-chromosome bearing) counterpart. As a consequence, when exposed to UV light during flow cytometry, X spermatozoa fluoresce brighter than Y- spermatozoa. As the spermatozoa pass through the flow cytometer in single file, each spermatozoon is encased by a single droplet of fluid and assigned an electric charge corresponding to its chromosome status (e.g. X-positive charge, Y-negative charge). The stream of X- and Y- droplets is then separated by means of electrostatic deflection and collected into separate collection tubes for subsequent processing.

Recently, a study published in 2006 indicated that mothers with toxoplasmosis have a significantly higher sex ratio of boys to girls. This has been discussed in connection with the manipulation hypothesis of parasites. Another study found a link between sex and the diet of the mother, but this may be due to statistical chance, and has yet to be confirmed.