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AIBU?

Share your dilemmas and get honest opinions from other Mumsnetters.

Original poster

When they're not actually brothers!

263 replies

3isthemagicnumbersoimtold · 28/06/2017 22:40

I have three children

DS is 10 and twin DS are 7. My BIL and SIL have a son who is 9. From when he was born they've always been very set that he would be their only child. Fair enough not my business.

Anyway my boys are very close and get on well with each other. twins are identical and very close and older DS is a good big brother to them.

They get on well with their cousin and see him once a week (perhaps every two weeks) at my MIL. He's a lovely boy too and they get on well.

Anyway, last week they were upstairs playing and nephew came downstairs very upset saying my oldest DS had been mean to him. I asked DS to come downstairs to explain what was going on. DS came downstairs and explained that my nephew (his cousin) had said to him that he's just as close to him as the twins and they're brothers too. I think DS was maybe a bit blunt and said that cousins weren't as closely related as siblings. Nephew said that my BIL and SIL had told him they were as close. I quietly said to DS that he shouldn't hurt nephews feelings and that he wants to be as close as my DS is to his twins brothers, it wasn't harming anyone and it's lovely that he feels close to them.

Anyway, that was that I thought. But no, i had a text from my SIL who said she thinks my DS is incredibly mean and rude for telling nephew that he is not as close to them. I don't even know what to reply to her. It's just bonkers! They're not brothers!

I feel like I've been dragged into a strange argument that biology and genetics would set straight! Aibu to just tell her to piss off?

OP posts:
PacificDogwod · 29/06/2017 16:32

Cousins are genetically not as close as brothers = biological fact and cannot be argued with.
Cousins can be socially as close to each other as if they were brothers. This may be different from family to family/cousin to cousin.

Your SiL sounds loopy. And somewhat defensive?

AGnu · 29/06/2017 16:40

I find the whole genetics thing fascinating. I know a family where 2 siblings married another pair of siblings. Presumably their DC are genetically closer than cousins who only share one side of the family but not as closr as siblings. Where would half-siblings fit into it though if one parent were to have a child with an unrelated adult? Would that child's siblings be more closely related to their cousins than their half-sibling?

CotswoldStrife · 29/06/2017 16:46

Looks like the SIL is not going to take the blame for giving her child the wrong idea here.

I don't see why your son should pretend he feels as close to his cousin as he does to his brothers. It's fine for the cousin to feel close to your son without it feeling the same on both sides.

mugginsalert · 29/06/2017 16:46

It's not on to blame a 10 year old for merely correcting something he knew not to be true. It's for her to support her son with any feelings he has about his family make up. She was unrealistic to expect you all to go along with her pretence, or even to understand it, given she'd not mentioned it before.

It might be nice (if it's true) for your DS to be able to respond with 'you're not our brother, you're our best special cousin' or somesuch but really it's not up to any adult to decide how he feels about anyone else. Perhaps your ds's could enlighten your poor dn about some of the annoying bits of having siblings as a counterbalance to the rosy view he's been given...

Lweji · 29/06/2017 16:52

@AGnu
From quick calculations, the offspring of the sibling pairs that got married would share (on average) 1/8+1/8 of their genes, so 1/4, which is similar to what they share with each aunt/uncle.
So, for those cousins to marry, genetically it would be similar to each marrying their uncle/aunt.

Cousins that were children of pairs of identical twins, would be like siblings and share 1/2 of their genes.

Lweji · 29/06/2017 16:53

It would be like feeling that you and your OH were also his parents. Would your SIL be happy with that?

PacificDogwod · 29/06/2017 17:08

While siblings have half their genes from each parents, they still can have very different genes as there's no (easy) way to determine what half they got from each parent. Which is way (obvious statement coming up) siblings can be quite similar to each other or totally different in appearance, personality, health.

I stand by SiL sounding loopy, sorry.

PacificDogwod · 29/06/2017 17:08

Social closeness obviously has nothing to do with genetic similarities.
Not-bloodrelated people can be as close as siblings, but are not siblings.

Gawd, the Institute of The Bleeding Obvious is doing well today Grin

Lweji · 29/06/2017 17:10

While siblings have half their genes from each parents, they still can have very different genes as there's no (easy) way to determine what half they got from each parent.

Indeed. Which is why I wrote "on average" earlier.

Then if you add epigenetics to that, it's even more complicated.

Lweji · 29/06/2017 17:12

Mind you, that genes, in this context, is basically shorthand for alleles (or, more accurately, for genome).

Chloe84 · 29/06/2017 17:22

She replied with "well don't let DS upset him like that again"

'I will not teach my children to lie.'

Chloe84 · 29/06/2017 17:24

Is that why none of my siblings look like our dad's side? Wow.

PacificDogwod · 29/06/2017 17:24

"well don't let DS upset him like that again"

"I am sorry he is so easily upset" - perfect non-apology, said with mild PA smile.

PacificDogwod · 29/06/2017 17:26

Lweji, I know you know your stuff.
I marvel at quite how different my 4 DCs are - same parents, same environment and they were SO different from the moment they drew breath.
It's fascinating Smile

MissEliza · 29/06/2017 17:41

I can't believe some of the bonkers stuff you read on MN. Imagine having to waste time on such a silly discussion.

Whocansay · 29/06/2017 17:57

She's bonkers. They are not brothers, and you OP, are REMARKABLY restrained!

Lweji · 29/06/2017 19:07

Lweji, I know you know your stuff
I know that you know that I know Grin. I just meant to add to your comment.

HappyFlappy · 29/06/2017 19:27

Lweji, I know you know your stuff

I know that you know that I know

Blimey - this is as complicated as the genetics.
Grin

lazycrazyhazy · 29/06/2017 19:32

I would be tempted to explain that while two people may be biologically closer two other people may be closer friends. Maybe they are too young for that though? My DH and my SonIL are both much closer and have more in common with a 1st cousin than their siblings....

PacificDogwod · 29/06/2017 19:34

... and I know what I don't know.
Unless I don't know what I don't know

Grin
Lweji · 29/06/2017 19:37
Grin That's important.
Rhubarbginisnotasin · 29/06/2017 20:38

Wait what if one brother has a son and the other brother has a daughter....cousin brother sister

Dont be daft. The female would say the male was her cousin brother and the male would say the female was his cousin sister.

Rhubarbginisnotasin · 29/06/2017 20:43

I think all this talk of genetics is ridiculous. Its obvious the Op's nephew meant they are like his brothers on an emotional level. It was harmless. He just wants to have others to belong to. Other cultures can make allowances for children born to siblings to share a special bond even in name only and I'd rather have that than the clinical nonsense this thread has been reduced to.

SvartePetter · 29/06/2017 20:46

My grandfather's brother married my grandmother's sister. My mum always referred to those cousins as her double cousins. They don't have a lot of similarities but I suppose there is a certain family ressemblence.

Completely unrelated to the OP, sorry....

Floggingmolly · 29/06/2017 20:47

Hear, hear, Rhubarb. It's a nine year old.