# How is my neice's baby related to me? And to my son?July 14, 2006 11:49 AM   Subscribe

My neice is due to give birth any day now to a little boy. How will her new son be related to me? (ie. grand-nephew?) And what will be his relationship to my son? Any help finding an online resource for determining relationships such as this would be appreciated.
posted by mezzanayne to Human Relations (11 answers total) 2 users marked this as a favorite

Cousin Calculator
posted by muddgirl at 11:54 AM on July 14, 2006

Wikipedia has a handy chart.
posted by Elsa at 11:54 AM on July 14, 2006

Says it's "Grand Nephew" to you and 1st cousin once removed to your son.
posted by muddgirl at 11:55 AM on July 14, 2006

posted by Gator at 11:57 AM on July 14, 2006

That answers that. Thanks for the help, everyone.
posted by mezzanayne at 12:03 PM on July 14, 2006

Best 'human relations' question ever.
posted by ElfWord at 8:06 PM on July 14, 2006

Huh! In Bangladeshi culture we don't have a "once removed" system. One generation above you and they're your aunts/uncles; one generation below and they're your neices/nephews.
posted by divabat at 8:21 PM on July 14, 2006

The "removed" thing is pretty logical, once you get the basic pattern:

1) The numbered "cousins" part refers to everyone in _the same_ generation, and how far they all are from their common ancestors. All the grand-kids from that same initial couple are "first cousins" to one another, because they're all one generation away from that first pair. (Although you wouldn't ever really put it this way, all the siblings from a given couple are effectively "zeroth cousins" to one another.) All the great-grandkids in the family who are two generations away are "second cousins" to one another, all the great-great-grandkids are "third cousins" to each other, etc.

2) The "removed" aspect describes the relationship between _different_ generations. It's sort of like finding a common denominator--you start with the broadest set of "cousins" you can find in a shared generation, and then count off how much one side is out of balance.
As an example, if you and I are in the same generation as second cousins, then you're a second cousin "once-removed" to my kids, since you're in a different generation than they are, by one. ("Once-removed" equals "one generation off-balance", if you look at it as a tree.) I'm the same thing to your kids, for the same reason in reverse. You're a "second cousin _twice_-removed" to my grand-kids, since there's a two-generation gap between you and them, and you're "2nd cousin _three_-times removed" to my great-grandkids, etc.

Our collective set of kids would all be "third cousins" to one another, since they're all once again evenly distant from the great-grandparents that you and I share, bringing the whole thing back into balance.

Hope that's not too complicated--it's actually the type of thing you could explain in 2 secs with some diagrams. (Also, it doesn't help straighten out the "great/grand-nephew" thing, or step-kids/step-parents. Sorry.)
posted by LairBob at 9:19 PM on July 14, 2006

In a diploid random mating population, your coefficient of relatedness (r) to your sister (or any full sib), is 0.5 -- both of you got half your genes from each of your parents. Your sister's kids are related to her by 0.5 (they got half their genes from her), so you're related to them (your nieces and nephews) by r = 0.5 * 0.5 = 1/2 * 1/2 = 1/4 = 0.25.

Your niece's son is related to her by 0.5, you're related to her by 0.25, so you're related to her son by 0.5 * 0.25 = 1/2 * 1/4 = 1/8 = 0.125.

Your son is related to you by 0.5, so he's related to your niece by the 0.25 you're related to her times the 0.5 he's related to you, so he's related to your niece by 0.25 * 0.5 = 1/4 * 1/2 = 1/8 = 0.125. He's related to her son by his relation to her (0.125) times her relation to her son (0.5 ) = 0.125 * 0.5 = 1/8 * 1/2 = 1/16. = 0.0625. (Or equivalently, by your relation to your niece's son, 0.125, times your son's relation to you, 0.5, equals again, 1/8 * 1/2 = 1/16.)

(Again, assuming a random mating population and no inbreeding, and diploidy -- humans are diploid; for haplodiploid insects, the equations are different, and so are the consequences for kinship and altruism.)

From W.D. Hamilton, your inclusive fitness is your own reproductive success plus the reproductive success of your kin times the coefficient of your relation to those kin. So your niece having a child increases your fitness one-fourth as much as you having a child; equally, if she has four kids, that increases your inclusive fitness as much as you having one kid of your own.

From Hamilton, we also we know that you should attempt to aid -- be altruistic to -- kin, if the cost to you is less than the coefficient of your relatedness to that kin times the benefit the kin receives: cost < r * benefit, where r is the coefficient of relatedness.

Your coefficient of relatedness to you son is 0.5. So you should be expected to aid your son if the benefit to him is twice (or greater) than the cost to you. (If the cost to you is higher, or the benefit to him is lower, you could have used those resources to benefit yourself or other (possibly potential) offspring.)

Your coefficient of relatedness to your niece is 0.25. So you should be expected to help your niece if the benefit to her is four times or greater than the cost to you.

Your coefficient of relatedness to your niece's on is 1/8, so you should aid him if his benefit is eight times the cost to you; your son should benefit him if that benefit is more than 16 times the cost to your son.
posted by orthogonality at 10:10 PM on July 14, 2006

Just to throw it out there, I would call my mother's aunt my great aunt, not my grand aunt. She would call me her great niece. This may be my family's aberration, but I think I've heard others call similar relationships the same.
posted by Monday at 1:19 AM on July 15, 2006

Monday writes "I would call my mother's aunt my great aunt, not my grand aunt. She would call me her great niece. This may be my family's aberration, but I think I've heard others call similar relationships the same."

My family does this as well; I actually believed it was accepted convention for quite some time.
posted by youarenothere at 7:59 AM on July 15, 2006

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