King Henry VIII's dream come true...

February 11, 2014 5:24 PM

Biologists and Staticians... what's going on here? There hasn't been a female born in my husband's family in two generations. Help solve the brothers' debate about what's causing this, and what the odds of our pregnancy being male or female is.

My side of the family - I'm female, have a brother and sister. No cousins, no other kids etc. My husband's maternal half-uncle has a little girl.

Pertinent Info -
Husband's paternal side:
Nan and Pa had two girls and a boy.
Female A - no kids
Male - 4 sons
Female B - 3 sons (too young to have thier own kids)

Male's four sons have thus far had:
Son 1 - 4 sons (ID twins + 2)
Son 2 - 1 son
Son 3 - No kids
Son 4 - We're pregnant.

Statistical fluke? Stacked deck? What's happening here?

posted by jrobin276 to Science & Nature (16 answers total)

I know nothing about statistics, but my husband's family was the same, nothing but boys. (I could give you the rundown but just trust me. There's a girl in there somewhere but aside from that, all boys.) Everyone on his side swore we would never have a female.

For our first child, their hypothesis played out and I have a two year old son currently torturing my cat. Then along came number two. My husband told me not to even bother looking at girl's names. So when our little girl came out, we were all surprised that he was missing a penis...

My point is I don't think family history has much bearing, each child has a fifty percent chance of being a boy or a girl.
posted by Jubey at 5:35 PM on February 11, 2014 [3 favorites]

Statistical fluke? Stacked deck? What's happening here?

Statistical fluke. It's like flipping a coin.
posted by nangar at 5:36 PM on February 11, 2014 [5 favorites]

There are a host of reasons for having only girls (there are many x-linked things that can go wrong leaving any progeny with a single X chromosome with lethal conditions) but having only male progeny is harder to link to genetics. I vaguely remember someone hypothesizing that it could relate to DNA packing in sperm but am having trouble finding articles related to that (my googlefu is weak this evening as I've got a wicked head cold).

The last time I looked into this it was four generations of four boys in each generation - which is much less statistically likely than your family tree.

The person asking was a friend who was married to one of the fourth generations' boys. They ended up having a boy and a girl so ... even unlikely statistics happen.
posted by sciencegeek at 5:41 PM on February 11, 2014 [1 favorite]

It's not like flipping a coin. When we were trying to get pregnant with our third, after having 2 boys, I looked into it and found something that said--this is like 8 years ago now so my numbers won't be perfect--that people who had 2 boys in under six years had something like a 70% chance of their next child also being a boy. I'm sorry I don't have time to replicate my googling and get better numbers, and all the whys and wherefores, but I was fascinated to learn that each pregnancy is not 50/50 but that there are factors that can skew the odds.
posted by not that girl at 5:44 PM on February 11, 2014 [2 favorites]

Though the probability of having third child of one gender is different, the probability of first child is still 50/50.
posted by mrfuga0 at 6:24 PM on February 11, 2014 [1 favorite]

This happened on husband's side of the family. No girls born since 1932. Our daughter born in 2012 broke the streak.
posted by tafetta, darling! at 6:32 PM on February 11, 2014

Given the number of families in the world, there have to be some with improbable-seeming streaks of boys. That's how probability distributions work.
posted by lollusc at 6:39 PM on February 11, 2014 [6 favorites]

I don't have any opinion about whether or not there are conditions that might cause a certain person to be more or less likely to have a boy child than a girl child, but presuming that it's just 50/50, the chance of a group of 11 kids^* being 11 boys is about 1 in 2000. On its surface that may seem terribly unlikely, but it's not really: It's unlikely for any specific family, but there are a whole lot of families; "1 in 2000" means "many in the world".

*: I know it's really 12 kids, but the two identical twins statistically count as one for this purpose, since the chance of one being a boy given that the other is a boy is 100%, not 50%.
posted by Flunkie at 6:39 PM on February 11, 2014 [4 favorites]

Statistical fluke. As pointed out above, it is a coin flip each time, and as with coin flips, ten heads in a row is memorable but HTTHTTHTTH excites no comment. Each outcome is equally likely.

My grandmother was one of five sisters; they all had daughters. Those daughters (including my mom) had -- excluding me -- nothing but daughters and my sister and cousins on that side have had nothing but daughters so far. It happens.
posted by ricochet biscuit at 6:41 PM on February 11, 2014

I am one of three boys. My father was one of two boys. His father was one of four boys and my great grandfather was one of three boys. Four generations of multiple boys. My brother had a boy as the first in that generation. My wife was pregnant. Everyone said she was carrying a boy. My daughter is a baseball fan if that helps. She was the first girl in my family for 5 generations.

I think you should ask for odds and bet girl. IF they really think it is more than a statistical aberration, let them back it up with odds that make your expected return positive.
posted by JohnnyGunn at 7:01 PM on February 11, 2014

Are they a family that loves cats? Pregnant women infected by cat parasite more likely to give birth to boys, say researchers
posted by Bentobox Humperdinck at 7:02 PM on February 11, 2014 [1 favorite]

"1 in 2000" means "many in the world".

It means you are even likely to find several examples among MetaFilter users.
posted by grouse at 7:32 PM on February 11, 2014

I believe it's not entirely a 50/50 chance each pregnancy (or at least the first pregnancy). Here's an article that references research about diet being a factor.
posted by crunchtopmuffin at 7:49 PM on February 11, 2014 [1 favorite]

This also happened on my husband's side of the family. No girls since 1950, until a cousin was born in 1994; four boys were born in that time. Then it was six girls in a row.
posted by Andrhia at 7:55 PM on February 11, 2014

This is just how statistics work. When something has a 50% chance of happening (and it is indeed roughly 50% despite the caveats people are giving above) you would expect to see streaks. If you didn't it would mean that the odds aren't exactly 50% but rather the results are a set pattern with no randomness.

Also you can't count the identical twins as two boys, that's cheating. They count as one boy for these purposes.
posted by Justinian at 11:39 PM on February 11, 2014

Odds of 10 boys being born in a row: approximately 1 in 1024. Even a small town will likely have families in which this has happened over the course of the last few generations.

Odds of 20 boys being born in a row: approximately 1 in 1,048,576. Large cities and smallish countries will likely have families in which this has happened over the course of the last few generations. There will be numerous instances in large countries.

Odds of 30 boys being born in a row: approximately 1 in 1,073,741,824. There are likely families on earth in which this has happened over the course of the last few generations.
posted by kyrademon at 5:21 AM on February 12, 2014 [3 favorites]