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Green-beard effects are genes that:

  1. Produce an effect that can be detected
  2. Produce preference to others with the same effect

Are there any examples of this in humans?

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Could you expand you question to make it more accessible to users, and thus easier to answer? What 'samples' are you interested in? Do you have an example? Thanks. –  Luke Jun 20 '12 at 11:10
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So... essentially you are looking for examples of dominant alleles with a clear phenotype? I do not understand your examples, though: racism, wars etc. are all but "easy" situations that definitely cannot be explained [just] in terms of genetics. Also, when you write "sample" do you mean "example"? I am asking because sample has a different meaning. –  nico Jun 20 '12 at 16:33
    
Essensially I am still confused. I feel that altruism toward those who are similar are very much a like altruism toward family members. Yes, it may not be pure genetic. Then what? How, mathematically, those traits reproduce? Does every such traits come with a complementary trait to like those with the traits? Still some part is mathematically missing. –  Jim Thio Jun 20 '12 at 16:37
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You cannot reduce everything to genetics. Ambient plays a role of paramount importance in all those situations. There are certainly a series (definitely not one) of genes that can influence how much altruist or racist or violent you are, but the education you are given and the culture in which you grow in are much more powerful in shaping your behaviour. –  nico Jun 20 '12 at 20:46
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I've reverted all the later changes, they confused the matter more than they helped in my opinion. –  Mad Scientist Jun 21 '12 at 12:48
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1 Answer

Your examples are way too broad. A green-beard effect only applies to the effects of a single gene or group of linked genes, not to just any trait. Racism and your Mongol war example are too complex to be explained by this effect. In reality examples will mostly be found in single-celled organisms where expression of a single protein can have whole-organism effects such as causing aggregation, or in larger organisms where some highly visible effect is possible such as a colour change.

There are very few real known examples of the green-beard effect, but four are listed on the Wikipedia page:

  1. The killing of red ant queens carrying a particular allele by workers with a different allele (Keller & Ross, 1998)
  2. Altruism in social amoeba resulting from homophilic adhesion of a protein (Queller et al., 2003)
  3. A multi-locus example in which similarly-coloured male lizards protect one another (Sinervo et al., 2006)
  4. A neat example in yeast whereby individuals sharing an allele for a particular locus selectively aggregate, preventing those without the allele from benefiting by proxy from their trait (Smukalla et al., 2008)

References

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Nice answer, just wanted to point out that obviously "altruism" in the amoeba cannot be extrapolated to altruism in men (not that you are saying that, but I can see such a comment coming) –  nico Jun 21 '12 at 5:15
    
@nico yes that's a good point, in this case it literally means sticking together –  Richard Smith Jun 21 '12 at 6:31
    
I asked why people are altruistic toward those who are similar to them, and they said green beard. Then here you said green beard don't work for humans. –  Jim Thio Jun 21 '12 at 12:57
    
Who is 'they'? The green beard effect simply describes one possible explanation for evolution of simple cases of altruism. It may or may not apply to humans, but no human example is known. –  Richard Smith Jun 21 '12 at 13:00
    
Perhaps you're talking about Winawer's answer here?. He doesn't mention humans, and specifically says it's more likely in bacteria, and that it probably isn't that widespread. –  Richard Smith Jun 21 '12 at 13:05
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