Is it possible for a woman to conceive from two different men and give birth to half-siblings?
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3$\begingroup$ To go even more strange parent relations then there was law suit by Washington state where mother wasn't mother to her children. While mother was able to prove being parent with pictures state obviously suspected fraud because DNA don't lie. After new tests appeared that mother has condition named chimerism. In her case that meant when she was fetus at very early stage then she had twin sister and she fused together with her twin sister who then became her uterus. So she was kind $\endgroup$– marsiltCommented Jan 21, 2023 at 7:18
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2 Answers
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Yes, this is possible through something called heteropaternal superfecundation (see below for further explanation).
Of all twin births, 30% are identical and 70% are non-identical (fraternal) twins.
Identical twins result when a zygote (one egg, or ovum, fertilized by one sperm) splits at an early stage to become twins. Because the genetic material is essentially the same, they resemble each other closely.
Typically during ovulation only one ovum is released to be fertilized by one sperm. However, sometimes a woman's ovaries release two ova. Each must be fertilized by a separate sperm cell. If she has intercourse with two different men, the two ova can be fertilized by sperm from different sexual partners. The term for this event is heteropaternal superfecundation (HS): twins who have the same mother, but two different fathers.
This has been proven in paternity suits (in which there will be a bias selecting for possible infidelity) involving fraternal twins, where genetic testing must be done on each child. The frequency of heteropaternal superfecundation in this group was found (in one study) to be 2.4%. As the study's authors state, "Inferences about the frequency of HS in other populations should be drawn with caution."
answered Nov 5, 2014 at 8:06
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7$\begingroup$ @Probably The frequency of HS in individual births is 0% ;). HS in all twins is (cautiously) presumed to be <<2.4% since this figure is only from "paternity suits involving fraternal twins" $\endgroup$– StephenCommented Nov 5, 2014 at 20:14
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$\begingroup$ So there is no danger that HS twins born long consecutive and die? Is it? $\endgroup$– ProbablyCommented Nov 5, 2014 at 20:44
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$\begingroup$ @Probably: there's certainly no guarantee that they'll die, since the court cases found living examples. There may or may not be an increased danger that they'll die compared with "ordinary" twins, the evidence here doesn't speak to that at all. $\endgroup$ Commented Nov 5, 2014 at 21:28
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3$\begingroup$ @Probably: You seem to be very confused about the subject of fraternal twins. They are conceived within a (very) short time window from each other. Hours, at best. As soon as the female body "realizes" it has conceived, it hormonally "shuts down" further conceptions. So, as fraternal twins are conceived within that small time window, grow at similar pace, and because there's no such thing as giving birth to only one twin but not the other, they are also born within a similarily small time window. There is no "wait till second child unwind". $\endgroup$– DevSolarCommented Nov 6, 2014 at 10:20
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2$\begingroup$ @Probably: There are two eggs. The mother can have sex with one man and both eggs are fertilised. The mother can have sex with the same man twice in a short time, one egg is fertilised the first time, one egg is fertilised the second time. And the mother can have sex with two men in a short time, one egg fertilised by the first man, one egg fertilised by the second man. $\endgroup$ Commented Nov 6, 2014 at 11:30
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A search on Google will show you that there have been documented cases where twins had different fathers, including at least one case where a paternity lawsuit follows and the mother admitted to her husband that she had an affair.
There are also cases where twins look very different although they have the same parents. Including cases where one twin looks white and one twin looks black. This can happen when you have one white and one black parent, the children can end up being quite white or quite black and twins can look different. And it can happen if both parents are mixed race; they can have children that are lighter or darker than both parents, and twins can be one lighter and one darker.
Twins looking different by coincidence are much more common than twins with different fathers; as mentioned earlier in cases where there was a paternity lawsuit, only 2.4% turned out to have different fathers. That number will of course depend on the behaviour of people.
One newspaper article http://www.theguardian.com/lifeandstyle/2011/aug/19/my-twins-have-different-fathers describes a case with two days between sex with the two fathers which is more than I thought possible. As an example of dissimilar twins see http://www.babycenter.com/0_strange-but-true-mixed-race-twins-one-black-one-white_10364936.bc showing a family who actually has two sets of twins with one quite light and one quite dark.
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3$\begingroup$ It would be great if you added some references to support your response! $\endgroup$ Commented Nov 6, 2014 at 11:34