# Identical twin = perfect sperm donor? **URL:** \ **Category:** Factual Questions\ **Created:** [November 26, 2003, 10:08pm UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460 "2003-11-26T22:08:58Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![KarmaComa](https://avatars.discourse-cdn.com/v4/letter/k/e36b37/32.png) [@KarmaComa](https://boards.straightdope.com/u/KarmaComa)\ **Post date:** [November 26, 2003, 10:08pm UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/1 "2003-11-26T22:08:58Z")
Ok, here’s a question: I have a mirror-image identical twin brother. Given that we are supposedly genetically interchangeable, would there be any difference between a child of mine and a child of his with the same woman? The reason this seems strange to me is that we have remarkably different behavioral dispositions. It seems weird that my child would be the same as his. For example, I am more creative, whereas my brother is more analytical. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [November 26, 2003, 10:47pm UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/2 "2003-11-26T22:47:28Z")
Well, within a given sperm-load, there is a lot of random variation, not to mention variation in whatever haploid ends up in the woman’s ovum. But for this variation, all children produced by a given couple would be identical. Now, if the child were given a paternity test, would it be possible to determine whether you or your brother was the father? Tricky question. [These guys](http://www.hopkinscountyattorney.com/childsupport/faq.htm) say no (“The father cannot be identified by these [DNA] tests if the two men are identical twins”) as do [these guys](http://www.paternitynet.com/art16.html) (“it would not be possible through DNA testing to determine which twin is the father”). Personality traits, though, seem largely the result of environment, so the “creative/analytical” thing is irrelevant. If you were sterile and wanted a child that resembled you, your twin brother would be as good a donor as you could ever find. ---
**Author:** ![sugaree](https://avatars.discourse-cdn.com/v4/letter/s/cc9497/32.png) [@sugaree](https://boards.straightdope.com/u/sugaree)\ **Post date:** [November 26, 2003, 10:52pm UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/3 "2003-11-26T22:52:28Z")
Yes, a child of his is genetically the same as a child of yours. In fact, if you two were to have children with separate women, they would be genetic half-siblings, not cousins. Of course, they would be cousins in every other way. > [@](#): > > \*Originally posted by KarmaComa \* > \*\*he reason this seems strange to me is that we have remarkably different behavioral dispositions. It seems weird that my child would be the same as his. For example, I am more creative, whereas my brother is more analytical. \*\* Why would that seem weird? You know from experience that two genetically-identical men can be completely unique individuals. Your child probably won’t resemble you any more than you resemble your twin. ---
**Author:** ![sugaree](https://avatars.discourse-cdn.com/v4/letter/s/cc9497/32.png) [@sugaree](https://boards.straightdope.com/u/sugaree)\ **Post date:** [November 26, 2003, 11:02pm UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/4 "2003-11-26T23:02:38Z")
I feel the urge to say that **Bryan Eker’s** post was not there where I hit submit. ---
**Author:** ![Mac\_Guffin](https://avatars.discourse-cdn.com/v4/letter/m/2bfe46/32.png) [@Mac\_Guffin](https://boards.straightdope.com/u/Mac_Guffin)\ **Post date:** [November 26, 2003, 11:25pm UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/5 "2003-11-26T23:25:07Z")
So then, if two identical twin brothers married two identical twin sisters, then their offspring would be genetic siblings? woah. ---
**Author:** ![AmbushBug](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ambushbug/32/4600_2.png) [@AmbushBug](https://boards.straightdope.com/u/AmbushBug)\ **Post date:** [November 26, 2003, 11:32pm UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/6 "2003-11-26T23:32:37Z")
On the related not-quite-a-hijack subject of the evolutionary desire to pass on your genes, from [here](http://www.commonsenseclub.com/Seeds.html): > [@](#): > > When the famous British geneticist J.B. S. Haldane was asked for whom he would sacrifice his life, he replied only half-facetiously, “for three brothers or nine cousins.” Either combination adds up to more than 100 percent of one’s own genes, and from an evolutionary point of view it makes more sense to die if that means the others can live. ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [November 27, 2003, 12:05am UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/7 "2003-11-27T00:05:58Z")
> [@](#): > > \*Originally posted by AmbushBug \* > On the related not-quite-a-hijack subject of the evolutionary desire to pass on your genes, As an identical twin, I have to protest that my brother attempting to pass on our genes by having sex with a fertile woman is **not** an acceptable substitution for me having sex with one … ---
**Author:** ![boofy\_bloke](https://avatars.discourse-cdn.com/v4/letter/b/9e8a1a/32.png) [@boofy\_bloke](https://boards.straightdope.com/u/boofy_bloke)\ **Post date:** [November 27, 2003, 3:14am UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/8 "2003-11-27T03:14:01Z")
Further, remember that “environment” includes the womb, where “identical” twins actually experience different lives, with different placement (often one foetus will dominate the other) and different blood form the placenta. Thus YOU are clearly diffenent in personality from your brother despite being genetically identical as far as we can currently measure. ---
**Author:** ![KarmaComa](https://avatars.discourse-cdn.com/v4/letter/k/e36b37/32.png) [@KarmaComa](https://boards.straightdope.com/u/KarmaComa)\ **Post date:** [November 27, 2003, 3:32am UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/9 "2003-11-27T03:32:09Z")
So all this means that I don’t have to wear a cup when I play cricket? Fantastic! What threw me is the fact that my brother and I are typically mirror-imaged. I’m left-handed and right-brained, and he’s right-handed and left-brained, but for some reason I was hung up on that being a result of genetics. Thanks! ---
**Author:** ![doctordoowop](https://avatars.discourse-cdn.com/v4/letter/d/ecc23a/32.png) [@doctordoowop](https://boards.straightdope.com/u/doctordoowop)\ **Post date:** [November 27, 2003, 6:39am UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/10 "2003-11-27T06:39:21Z")
Bryan- temperament/personality is mostly genetic, not environmental. There are countless identical twin studies- separated at birth & raised separately, to control for environment; all show a high percentage of concordance for mental illness-70% for bi polar, 50% for schizophrenia, and at least 50% or more for personality traits.(less sure of this number-certain of 1st two.) Genetically, if identical twins marry identical twins, the cousins will be siblings. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [November 28, 2003, 1:53am UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/11 "2003-11-28T01:53:02Z")
> [@](#): > > \*Originally posted by doctordoowop \* > \*\*Bryan- temperament/personality is mostly genetic, not environmental. There are countless identical twin studies- separated at birth & raised separately, to control for environment; all show a high percentage of concordance for mental illness-70% for bi polar, 50% for schizophrenia, and at least 50% or more for personality traits.(less sure of this number-certain of 1st two.) Genetically, if identical twins marry identical twins, the cousins will be siblings. \*\* Wellllll… okay. So? The fact that even identical twins can show personality variance, as with the OP and his brother, simply suggests that variance between parent and child can be at least as great. In any case, if the OP is concerned that his twin’s different personality would be passed onto the child, he should be aware that even if the child was _his_, odds are the kid would still think he was a fogey and a doofus. In other words, whatever the mix of influences are, genetic or environmental, there’s simply no way to predict how screwed up (i.e. unlike you) or normal (i.e. like you) your kid is going to be. ---
**Author:** ![KarmaComa](https://avatars.discourse-cdn.com/v4/letter/k/e36b37/32.png) [@KarmaComa](https://boards.straightdope.com/u/KarmaComa)\ **Post date:** [November 28, 2003, 1:41pm UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/12 "2003-11-28T13:41:22Z")
> [@](#): > > _Originally posted by Bryan Ekers \* > \*\* odds are the kid would still think he was a fogey and a doofus._\* Hey! I resemble that! ---
**Author:** ![mrsam](https://avatars.discourse-cdn.com/v4/letter/m/b5ac83/32.png) [@mrsam](https://boards.straightdope.com/u/mrsam)\ **Post date:** [November 28, 2003, 4:52pm UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/13 "2003-11-28T16:52:53Z")
> [@](#): > > \*Originally posted by boofy\_bloke \* > \*\*Further, remember that “environment” includes the womb, where “identical” twins actually experience different lives, with different placement (often one foetus will dominate the other) and different blood form the placenta. Thus YOU are clearly diffenent in personality from your brother despite being genetically identical as far as we can currently measure. \*\* Still, it is only the genes that are passed down, not the organism’s experiences. As the twins would be genetically identical, environmental interaction is irrelevant unless it somehow change the genes of the donor sperm (which is incredibly unlikely). ---
**Author:** ![Lord\_Ashtar](https://avatars.discourse-cdn.com/v4/letter/l/7ea924/32.png) [@Lord\_Ashtar](https://boards.straightdope.com/u/Lord_Ashtar)\ **Post date:** [November 28, 2003, 7:07pm UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/14 "2003-11-28T19:07:03Z")
[Bad Singing] But they’re cousins, identical cousins… [/BS] ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [November 28, 2003, 7:41pm UTC](https://boards.straightdope.com/t/identical-twin-perfect-sperm-donor/215460/15 "2003-11-28T19:41:17Z")
> [@](#): > > \*Originally posted by Mac Guffin \* > \*\*So then, if two identical twin brothers married two identical twin sisters, then their offspring would be genetic siblings? > > woah. \*\* Yep, they sure would. Legally, of course, they’d be cousins. So, the question might be: If the children lived in a state that allowed first cousins to marry, would they be able to do so? I’m not sure, but I’d have to guess that they would.