Are children of the same sex more likely in a family?

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Offline Matthew

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Matthew asked the Naked Scientists:

Love the show, have heard every minute since inception via podcasts! I'm only sad that I now have to wait a week between shows!

My question:  When I'm walking in a mall or store, it seems I much more often see families with kids of predominantly one sex.  For instance, it seems I'm more likely to see a 4-girl or 4-boy family than a 2-2 split. I realize many things may bias this... a mom may take only the girls out, or I more likely notice the more odd family.  Is there any basis for this. Would this more likely depend on the mom's physiology or the dad's?

What do you think?

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Offline JnA

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Are children of the same sex more likely in a family?
« Reply #1 on: 14/07/2008 07:37:09 »
it's the y that determines the sex of a child. So it's up to (future) dads to make sure the ratio is even.

there is some evidence that men in high stress jobs produce more girls... but this needs more peer review.

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Offline Matthew

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Are children of the same sex more likely in a family?
« Reply #2 on: 16/07/2008 02:57:22 »
Yes the Y determines sex, and this may all be wives' tales, that 1) X sperm and Y sperm behave differently, something to the fact that Y sperm are faster, but run out of steam faster, but X sperm are slower but can run longer, and 2) that the female chemistry also affects the sperm movement.  It may be vastly complex really.  I just wonder if anyone's ever done stats on predominance of one sex over mixing.