# Likelihood of same sex children? **URL:** \ **Category:** Factual Questions\ **Created:** [February 5, 2013, 1:07pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384 "2013-02-05T13:07:56Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Charley](https://avatars.discourse-cdn.com/v4/letter/c/97f17d/32.png) [@Charley](https://boards.straightdope.com/u/Charley)\ **Post date:** [February 5, 2013, 1:07pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/1 "2013-02-05T13:07:56Z")
Is there any evidence that a family is more likely to have several children of the same gender? Anecdotally it seems that my friends whose first child was a boy went on to have other boys. Similarly those who had a girl (me included) went on to have other girls. Obviously I have friends with the full set of children, as it were, but they seem to be outnumbered slightly by the repeaters. I recognise that this may well be confirmation bias on my part, but I wonder if anyone knows of any research done in this area? Is it supportable that some families (essentially some women) ‘have sons’ and some ‘have daughters’? Of course if gender selection were only down to probability, that would be impossible, but since there are all sorts of other factors at work, maybe it’s not. I have idly looked for this sort of research through Google Scholar in the past, but it’s not my field and I don’t have easy access to a real library these days, so - anyone know? ---
**Author:** ![astorian](https://avatars.discourse-cdn.com/v4/letter/a/ad7895/32.png) [@astorian](https://boards.straightdope.com/u/astorian)\ **Post date:** [February 5, 2013, 4:16pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/2 "2013-02-05T16:16:53Z")
If a couple has two kids, there’s a 50% chance that both kids will be the same gender. If a couple had three kids, there’s a 25% chance they’ll have three boys or three girls. I’m one of four boys. There was a 1 in 16 (about 7%) chance of that happening, just as there was a 1 in 16 chance my parents would have four girls. Not exactly long odds. Given all the families you’ve known, it’s not surprising you’ve met many whose kids are all-male or all-female. ---
**Author:** ![eclectic\_wench](https://avatars.discourse-cdn.com/v4/letter/e/ac91a4/32.png) [@eclectic\_wench](https://boards.straightdope.com/u/eclectic_wench)\ **Post date:** [February 5, 2013, 5:05pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/3 "2013-02-05T17:05:07Z")
> [@Charley](#): > > Is it supportable that some families (essentially some women) ‘have sons’ and some ‘have daughters’? Actually, it’s much more likely that some \*men \*‘have sons’ and some ‘have daughters’, not some women. On a chromosomal level, women have no input into the child’s sex: they’re contributing an X sex chromosome either way. It’s the man who contributes either an X chromosome, making a girl, or a Y, making a boy. So if a man’s X-chromosomed sperm are stronger than his Y-chromosomed ones for some reason, or vice versa, that would make him more likely to have children of one sex or the other. Obviously it’s far from that simple - it’s possible that the environment in a woman’s cervix, or something, could favour one set of sperm over the other - but at the most obvious level, the guy is the one whose chromosomes make that call. ---
**Author:** ![TheBori](https://avatars.discourse-cdn.com/v4/letter/t/ee7513/32.png) [@TheBori](https://boards.straightdope.com/u/TheBori)\ **Post date:** [February 5, 2013, 5:10pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/4 "2013-02-05T17:10:24Z")
Two data points: My brother has four daughters (2 each from 2 wives) I have 4 boys (one wife). It looks like my bro’s “X’s” swim better than his “Y’s”…and vice versa. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [February 5, 2013, 5:18pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/5 "2013-02-05T17:18:36Z")
> [@eclectic\_wench](#): > > but at the most obvious level, the guy is the one whose chromosomes make that call. It’s seldom that everything occurs that matters only at the most obvious level. Vaginal, cervical, and uterine environments are now thought to contribute to success and failure in the ‘sperm wars’, even down to a single individual’s sperm. ---
**Author:** ![President\_Johnny\_Gentle](https://avatars.discourse-cdn.com/v4/letter/p/5f9b8f/32.png) [@President\_Johnny\_Gentle](https://boards.straightdope.com/u/President_Johnny_Gentle)\ **Post date:** [February 5, 2013, 5:28pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/6 "2013-02-05T17:28:27Z")
> [@astorian](#): > > If a couple has two kids, there’s a 50% chance that both kids will be the same gender. If a couple had three kids, there’s a 25% chance they’ll have three boys or three girls. > > I’m one of four boys. There was a 1 in 16 (about 7%) chance of that happening, just as there was a 1 in 16 chance my parents would have four girls. > > Not exactly long odds. Given all the families you’ve known, it’s not surprising you’ve met many whose kids are all-male or all-female. This calculation assumes that the gender of each child is independent of the others. There is research which indicates that this is not the case, although it’s relatively close to true. ---
**Author:** ![Thudlow\_Boink](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thudlow_boink/32/320_2.png) [@Thudlow\_Boink](https://boards.straightdope.com/u/Thudlow_Boink)\ **Post date:** [February 5, 2013, 5:46pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/7 "2013-02-05T17:46:27Z")
> [@President\_Johnny\_Gentle](#): > > This calculation assumes that the gender of each child is independent of the others. Thank you! As I interpret the OP, it’s specifically asking whether this is true or not. No fair just assuming! > [@](#): > > There is research which indicates that this is not the case, although it’s relatively close to true. Got a link to such research? ---
**Author:** ![eclectic\_wench](https://avatars.discourse-cdn.com/v4/letter/e/ac91a4/32.png) [@eclectic\_wench](https://boards.straightdope.com/u/eclectic_wench)\ **Post date:** [February 5, 2013, 5:48pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/8 "2013-02-05T17:48:41Z")
> [@Qadgop\_the\_Mercotan](#): > > It’s seldom that everything occurs that matters only at the most obvious level. Vaginal, cervical, and uterine environments are now thought to contribute to success and failure in the ‘sperm wars’, even down to a single individual’s sperm. Right - that’s basically what I said, only I said it in less detail. My point was that the OP’s implication - that it’s the woman who determines the child’s sex - doesn’t fit with some basic facts. ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [February 5, 2013, 5:48pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/9 "2013-02-05T17:48:56Z")
Reminds me of the family who lived behind us when I was a kid. The father was big on passing down the family name, so they kept hoping the next kid was a boy. At last count, they had seven girls. And they lived in a small 2-bedroom, 1-bath house. ---
**Author:** ![Lightlystarched](https://avatars.discourse-cdn.com/v4/letter/l/eb8c5e/32.png) [@Lightlystarched](https://boards.straightdope.com/u/Lightlystarched)\ **Post date:** [February 5, 2013, 5:53pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/10 "2013-02-05T17:53:34Z")
I had 3 miscarriages - 1 was a boy (at 23 weeks), two unknown. Two healthy girl pregnancies full term. Order of pregnancies was: G, m/c, B(m/c), m/c, G. My biological mother had 3 girls and only girls. I tend to think that for whatever reason, my body does better with female embryos/fetii (?) and that maybe the 2 unknown m/c were boys. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [February 5, 2013, 5:55pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/11 "2013-02-05T17:55:36Z")
> [@eclectic\_wench](#): > > Right - that’s basically what I said, only I said it in less detail. My point was that the OP’s implication - that it’s the woman who determines the child’s sex - doesn’t fit with some basic facts. Hey, she had the pertinent chromosomes last! So it really is up to her. 😉 ---
**Author:** ![Kimstu](https://avatars.discourse-cdn.com/v4/letter/k/ecd19e/32.png) [@Kimstu](https://boards.straightdope.com/u/Kimstu)\ **Post date:** [February 5, 2013, 6:00pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/12 "2013-02-05T18:00:02Z")
**panache45** ’s example brings in another factor: the so-called “stopping rule”, or conscious family-planning decision to stop or continue having additional children depending on whether a particular gender distribution has been attained. As [this article](http://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1038&context=bio_fac&sei-redir=1&referer=http%3A%2F%2Fwww.google.com%2Furl%3Fsa%3Dt%26rct%3Dj%26q%3Dprobability%2520same%2520sex%2520siblings%26source%3Dweb%26cd%3D14%26ved%3D0CEQQFjADOAo%26url%3Dhttp%253A%252F%252Fdigitalcommons.calpoly.edu%252Fcgi%252Fviewcontent.cgi%253Farticle%253D1038%2526context%253Dbio_fac%26ei%3DYkcRUZXgHY260QHd84HoBw%26usg%3DAFQjCNGH0xnOJ5kUufNdba--_tMEbULxtA%26bvm%3Dbv.41867550%2Cd.dmQ#search=%22probability%20same%20sex%20siblings%22) notes, > [@](#): > > We previously analyzed data from the U.S. National Health Interview Survey (NHIS, 1998 to 2002) on families with two biological children (10 years of age and younger) and found that the distribution of families with two boys, two girls, and one boy + one girl did not statistically conform to a binomial distribution regardless of the boy/girl sex ratio used. Using the best estimate of the sex ratio from the data, we found that there were signifi- cantly more families with opposite-sex siblings than families with same-sex siblings. No biological mechanism could explain these results at the time. In the present study we conducted an analysis of the first two children in sibships of size 3 from the same data source and found that there are significantly more same-sex sibships than unlike-sex sibships. Combining the two sets of data for the first two children produced observed numbers in close agreement with the expected numbers. A hypothesis of parental choice (family planning) appears to be strongly supported as an explanation for the discrepancies in the two sets of data individually. For example, parents who have a boy and a girl (either order) as their first two children are more likely to stop having children (“stopping rule”) than are parents whose first two children are of the same sex. ---
**Author:** ![Richard\_Parker](https://avatars.discourse-cdn.com/v4/letter/r/35a633/32.png) [@Richard\_Parker](https://boards.straightdope.com/u/Richard_Parker)\ **Post date:** [February 5, 2013, 6:01pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/13 "2013-02-05T18:01:46Z")
> [@eclectic\_wench](#): > > Right - that’s basically what I said, only I said it in less detail. My point was that the OP’s implication - that it’s the woman who determines the child’s sex - doesn’t fit with some basic facts. If the woman’s body determines which sperm wins, then in no real sense is sex determined by the man. Indeed, the effects of the woman’s body would seem to be the only way in which sex could be “determined” in any meaningful sense. If I toss a million pennies in the air and the one that lands in my coffee cup is face-up, did I determine whether I saw Lincoln’s beard? ---
**Author:** ![brazil84](https://avatars.discourse-cdn.com/v4/letter/b/8491ac/32.png) [@brazil84](https://boards.straightdope.com/u/brazil84)\ **Post date:** [February 5, 2013, 6:04pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/14 "2013-02-05T18:04:09Z")
> [@Charley](#): > > Is there any evidence that a family is more likely to have several children of the same gender? [Yes.](http://www.nytimes.com/2009/01/06/health/06real.html?_r=0) > [@](#): > > In a study published in the journal Evolutionary Biology, the researcher, Corry Gellatly, examined the histories of more than 900 American and European families dating to 1600, involving more than half a million people. A child’s sex is always determined by the father, since men cast the deciding chromosome — either an X or a Y — while women produce eggs that carry an X chromosome. Mr. Gellatly found evidence that men carry a gene that determines the percentage of X and Y chromosomes in their sperm, and that the gene comes in three alleles, or versions. One produces mostly X chromosomes, another mostly Y, and the third yields equal numbers of both. If a couple has a child of gender X, it’s more likely that the father has genetic predisposition to fathering children of gender X. Therefore it is relatively more likely that the next child will also be of gender X. I would guess that there is also some input from the mother’s side but the same reasoning applies. And of course this assumes that the mother and father don’t use some kind of artificial sex selection technique. I recall reading somewhere that among Indian-American families with 2 daughters, the chances that the third child will be a son are a lot higher than 50%. ---
**Author:** ![President\_Johnny\_Gentle](https://avatars.discourse-cdn.com/v4/letter/p/5f9b8f/32.png) [@President\_Johnny\_Gentle](https://boards.straightdope.com/u/President_Johnny_Gentle)\ **Post date:** [February 5, 2013, 6:09pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/15 "2013-02-05T18:09:50Z")
> [@Thudlow\_Boink](#): > > Thank you! As I interpret the OP, it’s specifically asking whether this is true or not. No fair just assuming! Got a link to such research? I couldn’t find the reference I was thinking of, but this study does indicate that: [ [QUOTE=Bigger, et al.] We examined 1960-1994 birth records from Denmark and obtained information on 700,030 couples who gave birth to single infants. In these data, we observed a relation between sex ratio and family size, as reflected in the average birth order of the infants delivered. To explain this relation, we examined the sex of infants at birth and found a subtle but significant interaction with birth order, that is, birth of a male increased the likelihood that the next child would be male. [/QUOTE] ](http://aje.oxfordjournals.org/content/150/9/957.full.pdf) ---
**Author:** ![eclectic\_wench](https://avatars.discourse-cdn.com/v4/letter/e/ac91a4/32.png) [@eclectic\_wench](https://boards.straightdope.com/u/eclectic_wench)\ **Post date:** [February 5, 2013, 6:12pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/16 "2013-02-05T18:12:17Z")
> [@Qadgop\_the\_Mercotan](#): > > Hey, she had the pertinent chromosomes last! So it really is up to her. 😉 😃 > [@Richard\_Parker](#): > > If the woman’s body determines which sperm wins, then in no real sense is sex determined by the man. Indeed, the effects of the woman’s body would seem to be the only way in which sex could be “determined” in any meaningful sense. If I toss a million pennies in the air and the one that lands in my coffee cup is face-up, did I determine whether I saw Lincoln’s beard? No one’s saying the woman’s body determines which sperm wins. There’s some evidence that the woman’s body _contributes to determining_ which sperm wins, which is an entirely different thing. And see Brazil84’s post for evidence that the woman’s body isn’t in fact the only way in which sex is determined. ---
**Author:** ![Richard\_Parker](https://avatars.discourse-cdn.com/v4/letter/r/35a633/32.png) [@Richard\_Parker](https://boards.straightdope.com/u/Richard_Parker)\ **Post date:** [February 5, 2013, 6:25pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/17 "2013-02-05T18:25:21Z")
I think this is a linguistic debate over the word “determined” and what it means to contribute to determining, so I’ll leave it there. Interesting thread. ---
**Author:** ![Charley](https://avatars.discourse-cdn.com/v4/letter/c/97f17d/32.png) [@Charley](https://boards.straightdope.com/u/Charley)\ **Post date:** [February 5, 2013, 6:32pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/18 "2013-02-05T18:32:56Z")
Thank you all, and especially **brazil84** , that’s exactly the sort of thing I was looking for. And yes I was assuming there wasn’t a straight equal probability. And I did totally know about the father and the chromosomes, honest guvnor. I plead half-awakeness this morning. ---
**Author:** ![Doctor\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/doctor_jackson/32/32_2.png) [@Doctor\_Jackson](https://boards.straightdope.com/u/Doctor_Jackson)\ **Post date:** [February 5, 2013, 10:33pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/19 "2013-02-05T22:33:00Z")
My parents had: B, G, G I have: B, G, G Sister 1 has: G, G Sister 2 has: B,G So the disposition in my familiy is to have a male first, followed by female(s). Except for sister 1, who has always been a bit of a rebel. ---
**Author:** ![Bob\_X](https://avatars.discourse-cdn.com/v4/letter/b/4491bb/32.png) [@Bob\_X](https://boards.straightdope.com/u/Bob_X)\ **Post date:** [February 5, 2013, 10:50pm UTC](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384/20 "2013-02-05T22:50:18Z")
> [@eclectic\_wench](#): > > Actually, it’s much more likely that some \*men \*‘have sons’ and some ‘have daughters’, not some women. On a chromosomal level, women have no input into the child’s sex: they’re contributing an X sex chromosome either way. More than 50% of pregnancies terminate with early miscarriage that generally the woman is not even aware of, and some women may preferentially miscarry male children more often than female, or the reverse, for some reason (I don’t know if this is the case, just suggesting a reason why the above is not necessarily correct). [Next page](https://boards.straightdope.com/t/likelihood-of-same-sex-children/649384.md?page=2)