How does one prove paternity if the father has an identical twin?

Question

Lets say Alice gets pregnant and claims she slept with Bob and he is the father. She wants a paternity test to prove it. The problem is that Bob has an identical brother, Billy, who has the exact same genetics. A paternity test can prove one of them is the father, but not which one she slept with.

Presume that Alice had neither a long standing romantic relationship with Bob nor anyone that was a witness to the sexual act, thus making the question of who she slept with difficult to prove. Can Alice still get child support, or will she be denied because she can not definitively prove which man is the child's biological father? Can she even get a paternity test given that it would not be definitive proof which man was the father?

Answer 1

Can Alice still get child support, or will she be denied because she can not definitively prove which man is the child's biological father?

The legal standard is a preponderance of the evidence (i.e. more likely than not) and there is plenty of evidence that can be offered in addition to DNA evidence, such as testimony under oath from people in a position to know who was having sex with whom at the relevant times.

Contrary to a common misconception, testimony under oath is still solid evidence that can support a verdict on appeal.

Alice had neither a long standing romantic relationship with Bob nor anyone that was a witness to the sexual act, thus making the question of who she slept with difficult to prove.

It isn't that hard to prove.

Q to Alice's physician: Based upon an ultrasound, when did Alice conceive?

A: April 5-8, 2021.

Q to DNA expert: Based upon the DNA test, who could the father be?

A: Billy or Bob.

Q to Alice: Did you have sex with Billy between April 5-8, 2021?

A: No.

Q to Alice: Did you have sex with Bob between April 5-8, 2021?

A: Yes.

Q to Billy: Did you have sex with Alice between April 5-8, 2021?

A: No.

Q to Billy: Why not?

A: I was at the Shuffleboard World Cup in Tibet, I have time stamped pictures.

Q to Bob: Did you have sex with Alice between April 5-8, 2021?

A: -- if Yes, judge says he believes Bob and Alice and the case is over. -- if No, the judge decides who among Bob, Billy, and Alice the judge believes based upon other evidence.

Ultimately, the judge has to rule between the two based upon non-genetic evidence and resolve credibility disputes just as in any other case that doesn't involve DNA evidence (which is the vast majority of cases).

Also, the edge cases are few are far between. Identical twins are rare to start with, and few women have sex with more than one identical twin in the several day period when she could have conceived or didn't know which twin she had sex with. It has happened at least once in history (post-DNA testing), but you can probably count the number of times that it has ever happened on one hand.

For example, presumptions from cohabitation, marriage, and claims of paternity often resolve paternity disputes without DNA evidence.

Further, to the extent that there is good faith uncertainty (perhaps everyone agrees that the mother has sex with both twins on the only possible day of conception and nobody really knows), the downsides to a mistake in the larger cosmic sense of the overall paternity law system are minimal, as identical twins very rarely become deeply alienated from each other and instead tend to be close and intensely cooperative once they discover each other, and tend to be similar to each other in almost every respect depriving the child of little if the court gets it wrong. Realistically, identical twins are particularly likely to settle out of court so the judge doesn't have to decide.

In one of the only two actual cases I could locate that went to trial (in Brazil), both twins were ordered to pay child support because the evidence showed that they actively conspired with each other to confound the mother and the court regarding who the father was, and conspiracies can support joint and several liability.

The other case reported in a news story had convincing circumstantial evidence supporting one identical twin over the other that probably establish a presumption of paternity for one twin and not the other.

One of the twins, who cannot be named for legal reasons, went to court last summer in the hope of forcing the mother to grant him access to the child. Although his name is not on the birth certificate, he claims he is the only father the boy has known, cared for him every other weekend, provided financial support and was even known to him as 'papa'.

But then the man's relationship with his girlfriend broke down and the visits halted. When he began legal proceedings to prove his paternity, the mother made her claim that she had been sleeping with his twin at around the same time.

The twins have said they knew they were both having sex with the woman, but argue that only one had sex during the period of conception. Both refused to undergo a DNA test: the complainant refused to pay the £335 charge while his brother, who has since married and fathered children, does not consider himself involved in the dispute.

Now, however, Judge Jolin has asked the complainant to take a DNA test by 1 December to ensure he can claim even possible paternity, while his brother may also be tested.

(The second case is in Quebec and the cost of the test in pounds is apparently a currency conversion value.)

(It is possible in principle to distinguish even identical twins from each other with high coverage whole genome tests that would reveal a few random mutations in each twin out of billions of possible mutations, but it is currently prohibitively expensive to do so.)

Can she even get a paternity test given that it would not be definitive proof which man was the father?

Yes. This rules out all 4 billion men in the world minus two of them. It has great probative value, narrowing the list of possible fathers down to two.

Answer 2

british-columbia

In British Columbia, Part III of the Family Law Act says that the child's parents are the birth mother and the child's biological father.

Outside of the context of assisted reproduction, there are a series of presumptions that apply unless the contrary is proved. A "male person" is presumed to be a child's biological father in any of the following circumstances:

• he was married to the child's birth mother on the day of the child's birth
• he was married to the child's birth mother and, within 300 days before the child's birth, the marriage was ended by his death, a divorce, or voiding
• he married the child's birth mother after the child's birth and acknowledges he is the father
• he was living with the child's birth mother in a marriage-like relationship within 300 days before, or on the day of, the child's birth
• he has acknowledged that he is the child's father by having signed a statement or agreement

If by operation of the presumptions, more than one person may be presumed to be the biological father, then no presumption applies.

If parentage can be resolved by one of these presumptions (and based on the facts in the question, it isn't clear that any of the presumptions applies), that answers the question, unless someone attempts to prove that the presumption is incorrect.

If someone wants to disprove the presumption, or to establish parentage when no presumption applies, they can apply for an order declaring parentage. When hearing such an application, the judge will consider all relevant evidence, including testimony of parties and witnesses, physical evidence, genetic testing, expert opinion, etc. The burden is on the party seeking the order, on a balance of probabilities.

Answer 3

It may depend on the location of the dispute, but my understanding is that most states impose a preponderance-of-the-evidence standard in paternity actions. Alice therefore does not need to "definitively prove" who the father is; she merely needs to prove that it is more likely than not that Bob is the father.

Armed with the paternity test, Alice has already made it a 50/50 proposition that Bob is the father, but that is not sufficient to establish a preponderance of evidence. She will therefore need to provide some additional evidence identifying Bob. She might attempt to make this showing with a complicated forensic analysis that tracks his phone GPS data to her apartment nine months before the child was born, but it also might be as simple as saying that she can tell the difference between the two and the she knows it was Bob.

If it's enough for the judge or jury, then she'll likely be eligible for child support.

Answer 4

I am not a lawyer.

Fingerprints and other biometric markers are different on true identical twins.

There is at least a 2% chance and upto a 25% chance that one of the twins is a chimera. That means that DNA from some parts of the body do not match DNA from other parts. Perform the Paternity test using DNA from many different spots on each twin. Hair, Blood, Sputum, Skin and other places if at all possible such as the Kidneys or Liver.

The Impossible Crime (Unless You Know About Chimeras) A man accused of a crime while he was behind bars. Women told they are not the mothers of children they gave birth to. Has DNA gone mad? https://www.mcgill.ca/oss/article/critical-thinking/impossible-crime-unless-you-know-about-chimeras

Counter position but very very very old. MINNESOTA JOURNAL OF LAW, SCIENCE & TECHNOLOGY VOLUME 14 WINTER 2013 ISSUE 1 Essay: Chimeric Criminals by David H. Kaye https://conservancy.umn.edu/bitstream/handle/11299/144217/Chimeric-Criminals-by-David-Kay_MN-Journal-Law-Science-Tech-Issue-14-1.pdf