Superfecundation

Superfecundation is the fertilization of two or more ova from the same cycle by sperm from separate acts of sexual intercourse. The term superfecundation is derived from fecund, meaning the ability to produce offspring.

Heteropaternal superfecundation occurs when two different males father fraternal twins. When the parents of fraternal twins are involved in a paternity suit, the odds are about 1 in 40 that the children are actually half-siblings.^[1]

In common usage, the term superfecundation is often used instead of heteropaternal superfecundation. The terms are practically equivalent because, though it is speculated that superfecundation by the same father is a common occurrence, it can only be proven to have occurred when there are multiple fathers.^[2]

Conception

Superfecundation most commonly happens within hours or days of the first instance of fertilization with ova released during the same cycle. There is a small time window when eggs are able to be fertilized. Sperm cells can live inside a female’s body for 4–5 days. Once ovulation occurs, the egg remains viable for 12–48 hours before it begins to disintegrate. Thus, the fertile period can span 5–7 days. Ovulation is usually suspended during pregnancy to prevent further ova becoming fertilized and to help increase the chances of a full term pregnancy. However, if an ovum is released after the female was already impregnated when previously ovulating, there is a chance of a second pregnancy—albeit at a different stage of development. This is known as superfetation.

Heteropaternal superfecundation

Heteropaternal superfecundation is common in animals such as cats and dogs. Stray dogs often produce litters in which every puppy has a different father.

Though rare in humans, many cases have been documented. In 1810, American physician John Archer documented a case in which a white woman gave birth to mixed twins—one white, one mixed-race—after having sex with a black man and a white man within a short time. In 1994 a woman gave birth to twin girls named Skylar and Ariana who have different fathers. ^[3] In June 2008, a Texas woman gave birth to fraternal twins fathered by different men.^[4] In that case, a DNA test concluded that there was a 99.999 percent chance that the twins had different fathers. The twins' mother acknowledged having had intercourse with more than one man in a short period of time close to the conception date.

Use in mythology

In Greek mythology, Heracles and his twin Iphicles are examples of heteropaternal superfecundation, with Heracles fathered by the god Zeus and Iphicles by a mortal man Amphitryon.

In another Greek myth, Leda conceives four children (Helen of Troy, Clytemnestra, and Castor and Pollux) in the same night by two different men. Two are children of Zeus, who comes to Leda disguised as a swan, and two are the children of Leda's mortal husband, Tyndareus. Which men father which children varies widely among accounts, in some cases establishing that the Gemini twins Castor and Pollux are born of different fathers. The heteropaternal superfecundation involved in this myth is especially unusual, because instead of giving birth to the children, Leda lays eggs that hatch them.

Literature

• In John Steinbeck's novel East of Eden, the twin brothers Caleb and Aaron may have different fathers.
• In Bryce Courtenay's "Australian" Trilogy, twin brothers Tommo and Hawk Solomon have different fathers, and were conceived on the same day.
• In Kotomi Aoi's "Boku wa Imōto ni Koi wo Suru - Secret Sweethearts", the twins Yori and Iku are fathered by different men.
• In Zadie Smith's novel White Teeth, Irie becomes pregnant with twins after having sex on the same day with brothers Millat and Magid, themselves identical twins, thus making it impossible to establish paternity.

Television

On the NBC soap opera Days of our Lives, a character named Sami Brady has fraternal twins born of two different fathers after having sex with both men within hours of each other. Similarly, the character Blake Marler on CBS's Guiding Light initially believes her twins have different fathers, but they are later proven to both be her husband's biological children. On One Life to Live in 2001, longtime heroine Victoria Lord Davidson discovers her twin daughters have different fathers.

See also

• Chimerism
• Mixed twins

References

1. ^ Wenk RE, Houtz T, Brooks M, Chiafari FA (1992). "How frequent is heteropaternal superfecundation?". Acta geneticae medicae et gemellologiae 41 (1): 43–7. PMID 1488855. "The frequency of HS among dizygotic twins whose parents were involved in paternity suits is 2.4%" 
2. ^ James, William H. (1980). "Gestational age in twins". Archives of Disease in Childhood 55: 281–284. PMC 1626817. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1626817. Retrieved 2011-03-17. 
3. ^ "Is it possible for fraternal twins to have different fathers?" from The Straight Dope
4. ^ "Two Twins, Two Dads: DNA Test Proves “Twins” Born to Different Fathers" from Discover Magazine Blog

External links

• "Is it possible for fraternal twins to have different fathers?" at The Straight Dope
• Lu et al. (1994). "Paternity Identification in Twins with Different Fathers". Journal of Forensic Science July; 39(4), 1100-2.
• Gawker (May 18, 2009)
• Doctors Discover Dallas Twins Have Two Different Dads. http://www.foxnews.com/story/0,2933,520524,00.html