Evolution type question

[CallMeIshmael]

I was thinking about this topic yesterday, and wonder if any of you know of any research done on it, or have thought of it yourselfs...


Friend of mine is an identical twin. So, when her sister has a child, she will be of the same relatedness to that child as she would her own child (0.5) but will socially call the child a neice or nephew.


Now, evolution has evolved us to the point (Sharkey, dont hijack the thread pls) where we of course care more for our own children than our neices/nephews, laregely due to the increased genetic interest.


Thus, it would make sense for my friend to care about her identical sisters children more than her brothers children.

Has anyone dont a study on this?

[diebitter]

Don't know about a study on humans and 'caring', but simpler forms do indeed tend to conform to conferring 'caring' to those individuals that have genetic relatedness (or given the circumstances, should have...cuckoos are completely unrelated, but exploit behaviours grounded in through caring for your offspring)

And the degree of caring is usually directly proportional to the relatedness.

Sorry, can't think of any specific studies to justify these statements, I just know them from distant memory of reading assorted ecology/evolutionary papers and journals.

[Metric]

Very interesting and original thinking! I have no idea!

[madnak]

How would an organism identify a twin? Is the incidence of identical twins large enough to result in selective pressure toward specialized "twin behavior?" Do we have some way of deciding how similar someone else is to us genetically, and act based on that? Or are our actions based more on social behavior?

Imagine the twins are separated at birth. Twin A develops a relationship with her brother while Twin B grows up in a separate household and develops a relationship with her adoptive brother. If, during adulthood, Twin A and Twin B were to meet (basically as strangers) could they develop as close a bond as they have with their brothers?

[CallMeIshmael]

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How would an organism identify a twin? Is the incidence of identical twins large enough to result in selective pressure toward specialized "twin behavior?" Do we have some way of deciding how similar someone else is to us genetically, and act based on that? Or are our actions based more on social behavior?

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That is basically the question.


There IS phenotype matching used in determing kin, but I'd have to imagine that social indentities matter WAY more.

But, at the same time, I would bet there would be SOME preference given to the neice/nephew of an identital twin simply based on phenotype matching.


I have also assumed that this is SOOO rare, that a specific mechanism involving identical twins wouldnt have evolved. (phenotype matching is, of course, a general mechanism)

[CallMeIshmael]

I cant belive I typed "yourselfs" in the OP

[vhawk01]

Right, the idea is that organisms developed family structures because those that happened to exhibit this behavior were more likely to pass along their genes and see their genes survive. While I guess I can imagine that there would be a selective advantage to those who were both able to recognize that a twin's child was as closely related to it as its own children and act accordingly.

It would be first necessary, I think, that we would have some way of determining who among our family carries the most of our genes. Did you know that it is possible, though not likely, that I am more closely related to you than I am to my own grandfather?

[SWB]

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Now, evolution has evolved us to the point (Sharkey, dont hijack the thread pls) where we of course care more for our own children than our neices/nephews, laregely due to the increased genetic interest.

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Not necessarily. Many apes live in communities in which the young are raised by the group as a whole, rather than only being cared for by their parents. It's also pretty common for stone age-era human tribes to organize themselves in extended families, though we only have a few isolated examples to study. So I don't think it's necessarily correct to say that humans are biologically predisposed to care about their own young more than those of a sibling; we've developed a society where people act that way, but lots of aspects of the way we act don't map well to how our ancestors probably acted in the 150000 or so years before civilization really got rolling.

[CallMeIshmael]

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Not necessarily. Many apes live in communities in which the young are raised by the group as a whole, rather than only being cared for by their parents. It's also pretty common for stone age-era human tribes to organize themselves in extended families, though we only have a few isolated examples to study. So I don't think it's necessarily correct to say that humans are biologically predisposed to care about their own young more than those of a sibling; we've developed a society where people act that way, but lots of aspects of the way we act don't map well to how our ancestors probably acted in the 150000 or so years before civilization really got rolling.

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Im not saying others dont ever raise the young, just that, on average, people care about THEIR young more than the young of others.

Id be open to studies, but I believe this to be a pretty constant observation through the sexual species

[CallMeIshmael]

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Did you know that it is possible, though not likely, that I am more closely related to you than I am to my own grandfather?

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No its not.


You are related to your grandparents by 0.25, and me by ~0

[vhawk01]

No, thats not true at all. You are likely, on average, to have approximately 25% of your genes from each of your grandparents. But there is absolutely no guarantee that you will share any. This is actually an important point. From an evolutionary perspective, 'you' is essentially a population average of all of your genes. So, your dad is exactly made up of half genes from his mother and half from his father. However, it is at least theoretically possible that, in making you, you managed to get exactly the half of your fathers genes that he got from his mother and none that he got from his father. In this fashion, you receive exactly none of your grandfather's genes, and are not related to him in any way.

Actually, you are still related to him in two ways. First, you are still geneologically related, although this is really a useless distinction, biologically. And you are also still related to him in that all people are related. But yes, it is possible that you can be more related to someone you have never met than your own grandfather.

[tolbiny]

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Now, evolution has evolved us to the point (Sharkey, dont hijack the thread pls) where we of course care more for our own children than our neices/nephews, laregely due to the increased genetic interest.

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Not necessarily. Many apes live in communities in which the young are raised by the group as a whole, rather than only being cared for by their parents. It's also pretty common for stone age-era human tribes to organize themselves in extended families, though we only have a few isolated examples to study. So I don't think it's necessarily correct to say that humans are biologically predisposed to care about their own young more than those of a sibling; we've developed a society where people act that way, but lots of aspects of the way we act don't map well to how our ancestors probably acted in the 150000 or so years before civilization really got rolling.

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As far as apes go chimpanzees are not aware of whom the father is due to the mehtods of mating so it behoves all higher level males (the ones who get a shot at any ovulating female) to treat all infants equally since they are all equally likely to be their's. Gorilla males live in a harem so all children are theirs (and if a new male takes over most infants by the previous dominant are killed) and it would not be advantageous for a female to kill other infants as they would be ostracized from the group and would gain nothing.
People, imo, are generally predisposed to care for what is familier. The more time you spend with your neices and nephews the more attached you will be.

[HLMencken]

People care about what is theirs, not just what is "related"--it just so happens that their kids generally are related, thus the correlation. Adopted parents care for their children more than a random kid on the street, who is just as related to them as their adopted kid.

[CallMeIshmael]

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No, thats not true at all. You are likely, on average, to have approximately 25% of your genes from each of your grandparents. But there is absolutely no guarantee that you will share any. This is actually an important point. From an evolutionary perspective, 'you' is essentially a population average of all of your genes. So, your dad is exactly made up of half genes from his mother and half from his father. However, it is at least theoretically possible that, in making you, you managed to get exactly the half of your fathers genes that he got from his mother and none that he got from his father. In this fashion, you receive exactly none of your grandfather's genes, and are not related to him in any way.

Actually, you are still related to him in two ways. First, you are still geneologically related, although this is really a useless distinction, biologically. And you are also still related to him in that all people are related. But yes, it is possible that you can be more related to someone you have never met than your own grandfather.

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Ohh, I see what you're saying. I actually assumed you made the assumption that all people are retlated by 0.99 or something, because of common genes in all humans.

Yes, technically you could get 0 genes from your GF. But, the probability of this is so close to 0, we can assume it is 0.

[CallMeIshmael]

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People care about what is theirs, not just what is "related"--it just so happens that their kids generally are related, thus the correlation.

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This is simply not true. And countless studies have shown this. Relatedness is a HUGELY correlated with care.


Also, you cant compare adopted kid to kid off the street, because the person knows one WAY more than the other.

I mean, I dont claim bonds cant form between non genetically related people, just that bonds between genetically related people are much stronger than would be predicted based soley on common interests / time spent together, etc... and that there is a strong correlation with the degree of relatedness

[HLMencken]

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People care about what is theirs, not just what is "related"--it just so happens that their kids generally are related, thus the correlation.

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This is simply not true. And countless studies have shown this. Relatedness is a HUGELY correlated with care.


Also, you cant compare adopted kid to kid off the street, because the person knows one WAY more than the other.

I mean, I dont claim bonds cant form between non genetically related people, just that bonds between genetically related people are much stronger than would be predicted based soley on common interests / time spent together, etc... and that there is a strong correlation with the degree of relatedness

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But the degree of relatedness (in terms of kin) is the same in both cases (in your niece/nephew case and my adopted kids case--comparing blood and non-blood relations is off topic). You are saying when relatedness is the same in term,s of kinship, but certain traits are more prevalent, will the relationship change? This is the same as asking will a father love/care for one child more because more of his traits are inherent in that child.

[CallMeIshmael]

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You are saying when relatedness is the same in term,s of kinship, but certain traits are more prevalent, will the relationship change? This is the same as asking will a father love/care for one child more because more of his traits are inherent in that child.

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Relatedness is NOT the same, and that is the whole point of the question.

The relatedness to the child of you identical twin is the same as it is to your child (0.5)

[HLMencken]

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You are saying when relatedness is the same in term,s of kinship, but certain traits are more prevalent, will the relationship change? This is the same as asking will a father love/care for one child more because more of his traits are inherent in that child.

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Relatedness is NOT the same, and that is the whole point of the question.

The relatedness to the child of you identical twin is the same as it is to your child (0.5)

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I meant relatedness in terms of "it is my brother's son and thus I am the uncle." I understand the point of the post. That's why I asked about adoption in which case relatedness by your definition is both the same (0) but obviously the caring of the parent is still greater than say an aunt. You also care for your child greater than your p[arent even though you have the same relatedness by your definition (0.5). My other point was that your 0.5 number is never really 0.5 in observable traits. 2 children are equally related to a parent but may be vastly different in how much each displays the traits of one parent versus the other.

I was just raising these points to show that this question is more difficult than assuming this situation is somehow different than other "relationship vs. caring" scenarios. Not provioding an answer, just providing more alternative views that may shed light, or may not.

[CallMeIshmael]

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That's why I asked about adoption in which case relatedness by your definition is both the same (0) but obviously the caring of the parent is still greater than say an aunt.

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Im not sure Im following... do you mean the aunt of the adopted child? If so, yes.. but, again, that has nothing to do with genetics, the child just spends more time with the adopted parents, than the adopted aunt

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You also care for your child greater than your p[arent even though you have the same relatedness by your definition (0.5).

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This is because a child has significantly higher reproductive value than a parent. Since, in the OP, we are discussing individuals of comparable age, this isnt really relevant.

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My other point was that your 0.5 number is never really 0.5 in observable traits. 2 children are equally related to a parent but may be vastly different in how much each displays the traits of one parent versus the other.

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Keep in mind that all of this goes on below the conscious thought. I mean, no one actively goes out and says "I care about my aunt twice as much as a do my cousin of the same age," but this view comes out when tests are done on the participants who indirectly reveal these preferences.

Similarily, even though two brothers may differ in how much of each trait of their parents they display, it doesnt mean that phenotype matching doesnt instinctively lead the parents to know they are related by 0.5.

And this really goes back to the question: Is phenotype matching strong enough to see that the child of the twin is (genetically) your child?

[chrisnice]

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And this really goes back to the question: Is phenotype matching strong enough to see that the child of the twin is (genetically) your child?

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No. Obviously there is alot to relatedness but conceiving, birthing and raising the child is what is going to do the majority of the bonding.

To reiterate a point made earlier that wasnt too clear. You will care more for your adopted child than you will for your niece or nephew.

Also I do suspect that twins feel more connected to their twins children than to other siblings children, but I think its probably because the twins have a much stronger connection themselves.

[CallMeIshmael]

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To reiterate a point made earlier that wasnt too clear. You will care more for your adopted child than you will for your niece or nephew.

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You are comparing apples to oranges.

Of course someone cares about their adopted child more than their biological neice, THEY LIVE WITH THEM AND IT IS THEIR SOCIAL RESPONSIBILITY.


I am comparing two neices, both of which do not live with you, and you spend comparable time with each, but one of which has a higer degree of relatedness to you.

[chrisnice]

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To reiterate a point made earlier that wasnt too clear. You will care more for your adopted child than you will for your niece or nephew.

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You are comparing apples to oranges.

Of course someone cares about their adopted child more than their biological neice, THEY LIVE WITH THEM AND IT IS THEIR SOCIAL RESPONSIBILITY.


I am comparing two neices, both of which do not live with you, and you spend comparable time with each, but one of which has a higer degree of relatedness to you.

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Probably the one with the parent with whom you are the closest.

And if somehow all the relationships are exactly the same except for the genetic makeup of one child vs the other then I suppose one would side with closer relatedness.

[The Funky Llama]

I think the answer to your question is that evolution has endowed us with certain behavioral tendencies that maximize our evolutionary fitness in an environment where certain situations happen more often than others.

For example, a mother might identify her children when she gives birth to them (imprinting) and because they share, on average, half of her genes, she will care for them more than an unrelated individiual.

However, since the case you describe is rare (identical twins), there is really no reason why a more discriminitative ability should evolve. If identical twins were very common, it would make sense for an identical twin to somehow "realize" that they should care for their twin's children as much as their own. As you know, humans don't consciously calculate relatedness and base their behavior on the result. Rather, they behave based on evolved instincts and tendencies that are have evolved over hundreds of thousands of years. These instincts are what is based on relatedness. These instincts influence behavior, but do not control it.

Evolution is kind of like poker in some ways...it depends on both magnitude (how a certain behavior/instint will affect fitness when it does have an effect) and frequency (how often will it have an effect).

Also, as others have pointed out, there is the issue of parental certainty. Even if you are related to your son to the same degree that you are related to your nephew, we are usually more certain of our own child's paternity.