It used to be regarded as a myth, but today we have cases of superfecundation in humans.
Superfecundation is the fertilization of two or more ova from the same cycle by sperm from separate acts of sexual intercourse. Heteropaternal superfecundation occurs when two different males father fraternal twins. 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.
The word which came from the Greeks was probably gotten from cats and dogs, which can bear litters in which each offspring is from a different father. Stray dogs often produce litters in which every puppy has a different father; they look so dramatically different from breed to breed that a discrepancy in paternity was bound to be noticed. It wasn’t however until relatively recently that superfecundation in humans was discovered.
I believe the incidence of superfecundation was not noticed in humans earlier because of the values the world once embraced. People hardly had multiple s*x partners, and for those who had, s*x wasn’t something they had with different men in a short space of time.
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. Now, tell me why we can’t have several cases of superfecundation today when our value system has dropped so low that s*x isn’t just a big deal anymore.
While it’s proven that it occurs, scientists obviously want to know how often superfecundation happens. The only way to test how often superfecundation occurs is performing genetic or blood tests on fraternal twins, and seeing how many have two different fathers. The data varies hugely. One test shows that while there are only about three cases of heteropaternal superfecundation in an overall test database of 39,000 records, but the rate goes way up when the parents of twins are in a paternity suit. About 2.4 percent of tested twins, in those cases, were heteropaternal. Another study suggests heteropaternity among twins in the general population to be as high as one pair in four hundred and estimates that one in twelve sets of fraternal twins are the result of superfecundation, if not superfecundation by two different fathers.
A Turkish man has decided to divorce his wife after DNA tests showed he was the father of only one of their twin boys.
smh.com.au on January 31, 2010 published this;
“The Turkish daily newspaper Sabah reported the security guard from Istanbul, identified only as A.K., had DNA tests done on the three-year-olds after becoming suspicious his wife had been unfaithful.
The tests established with a 99.99 per cent certainty that the man was the father of only one of the boys, adding that the result was confirmed by a forensic medicine institute upon the request of the court handling the divorce case.
The mother, identified as C.K., had maintained a relationship with a lover she had dated before her family forced her to marry A.K., the newspaper said.
The phenomenon of twins with different fathers – known as heteropaternal superfecundation – is very rare in humans but more common in animals such as cats and dogs.
It becomes possible in rare circumstances when a woman produces two ova in a menstrual cycle, said Professor Rusen Aytac, head of the gynaecology department at Ankara University’s medical faculty.”
The general belief is that males could have offspring with many females at once, but females could only get one genetic mate at a time, but this doesn’t hold with superfecundation, which has shown a female equally has a chance to combine her DNA with many partners as well.
Could this have had a significant evolutionary effect on animals? Is there any way human development could be affected by superfecundation? This is an interesting line of research whose findings I’d love to read about soon.