Random Question About Genetic Traits

[Rduke55]

[ QUOTE ]
[ QUOTE ]
By not desirable do you mean harmful to reproductive success, or just not helpful?

[/ QUOTE ]

Harmful to reproductive success. Specifically his own. He could be helpful to the reproductive success of others.

[/ QUOTE ]

If those others are his relatives than this could work if, in your martyr example, his sacrifice would result in them having enough kids.

[Praxising]

[ QUOTE ]
Let's call it a "Martyr Gene". A tribe needs a martyr to survive, but the martyr would not live long enough to reproduce. Naturally, he wouldn't pass on the gene.


[/ QUOTE ]

Yes there are. The kind of thing you are talking about is called "altruism." The gene may not be passed by this carrier, but this sort of gene would be a double recessive, so that this individual's brother or sister, possibly having one copy, will pass that copy along.

Some lethal genes are not selected-for themselves, but get passed along in "piggyback" fashion. That is, they are located near a selected-for gene on the chromosome. When crossing over occurs, genes clumped together, get crossed together.

Sickle-cell genes are highly selected-for in populations where malaria is prevalent, even though having two of them is fatal. So having a single gene for sickle cell anemia is common to about 50% of those populations. That's a balanced polymorphism.

Gayness, for want of a better word, has selective advantages because we used to be a family-oriented culture. That is, we are social primates organized into family groups. The purpose of biological life is production and reproduction: staying alive and passing on your genes. To keep offspring alive long enough to reproduce themselves and pass on those genes, it makes reproductive sense to have as many resources as possible - protection, food, and so forth. Because siblings share genes, a non-reproducing ("gay") member of the family group, provides more protection for the young and can acquire more food resources. That member's genes reside in the offspring also.

Ejecting gay persons from our families and communities is counter to reproductive success for the population as a whole.

[ZeeJustin]

Awesome. Thanks for the answers everyone.

[All-In Flynn]

Sorry to thread-jump, but...

[ QUOTE ]
Sickle-cell genes are highly selected-for in populations where malaria is prevalent, even though having two of them is fatal. So having a single gene for sickle cell anemia is common to about 50% of those populations. That's a balanced polymorphism.

[/ QUOTE ]

It is, yes, 1 gene = fitter (and reproductive) 2 genes = quite unfit (though presumably even more resistant to malaria [img]/images/graemlins/wink.gif[/img] ) and less likely to reproduce. I cannot see how from there you get:

[ QUOTE ]
Gayness, for want of a better word, has selective advantages because we used to be a family-oriented culture. That is, we are social primates organized into family groups. The purpose of biological life is production and reproduction: staying alive and passing on your genes. To keep offspring alive long enough to reproduce themselves and pass on those genes, it makes reproductive sense to have as many resources as possible - protection, food, and so forth. Because siblings share genes, a non-reproducing ("gay") member of the family group, provides more protection for the young and can acquire more food resources. That member's genes reside in the offspring also.

[/ QUOTE ]

What is this - eusociality in early human primates? Sure, I understand the notion of kin selection, but time and again various eminently plausible ideas run into the problem that a gene which causes its bearer to be less likely to reproduce must have a profound effect on the probability of its kin to survive in order for this 'back-door selection' to occur. Where are you getting this? I mean it's a nice theory, I suppose it could be true - I just don't see it. It appears as though you've started with the idea that gayness must be reproductively fit (not unreasonable) but that leads you, as soon as you see a plausible evolutionary niche for it, to proclaim this as established fact. Is there some documented evidence that gay people are better at looking after kids? That people feel a sense of primal 'rightness' (similar to that say of catching a fish, gutting and cooking it yourself) when they leave their children in the care of a gay relative? Such a feeling would not be real evidence of any particular kind - but it is what I would expect to find if what you say is the complete truth or even a sketch of it.

[ QUOTE ]
Ejecting gay persons from our families and communities is counter to reproductive success for the population as a whole.

[/ QUOTE ]

Not anymore, by your own lights. I say ejecting gay persons from our families and communities is morally repugnant on the grounds of human liberty.

[tolbiny]

[ QUOTE ]

What is this - eusociality in early human primates? Sure, I understand the notion of kin selection, but time and again various eminently plausible ideas run into the problem that a gene which causes its bearer to be less likely to reproduce must have a profound effect on the probability of its kin to survive in order for this 'back-door selection' to occur.

[/ QUOTE ]

Living in human society has skewed your vision of what happens in the natural world. The majority of organisms born don't reproduce, huge amounts die between the fertilized egg -> reproductive egg stage. Since most animals don't live to reproduce the loss of one who loses all possibility only costs a fraction of what you might think, thus the beneficial effect doesn't have to be profound at all.

[All-In Flynn]

I don't see this reflected in apes. Ants, yes. Vertebrates tend to invest far more in one batch or litter (to varying degrees) - primates more than most vetebrates, and humans more than any other primate. The beneficial effect of any gene tending against its bearer reproducing must, I think, be of a corresponding degree - not shown.

Now I realise that it may be true that, say, the majority of male apes do not reproduce. Do we then see that such apes as are observed to practice something like homosexuality (can't remember which specific ones, something like 'Barber apes' but I can't quite remember it)are given responsibility for the care of the group's young? And is this role assigned to gays of both genders?

It seems more plausible to me that if there was a pressure exerted in favour of gayness, the (male) gays would far more likely be hunters or soldiers. I can see how this kind of primitive labour division might result in fewer orphaned offspring, which might in turn mean less waste... but it's difficult to model this kind of waste-avoidance as directly beneficial without resorting to group-selectionism.

[Leaky Eye]

Do you mean bonobo chimps?

[Praxising]

[ QUOTE ]
[ QUOTE ]
Gayness, for want of a better word, has selective advantages because we used to be a family-oriented culture. That is, we are social primates organized into family groups. The purpose of biological life is production and reproduction: staying alive and passing on your genes. To keep offspring alive long enough to reproduce themselves and pass on those genes, it makes reproductive sense to have as many resources as possible - protection, food, and so forth. Because siblings share genes, a non-reproducing ("gay") member of the family group, provides more protection for the young and can acquire more food resources. That member's genes reside in the offspring also.

[/ QUOTE ]

What is this - eusociality in early human primates? Sure, I understand the notion of kin selection, but time and again various eminently plausible ideas run into the problem that a gene which causes its bearer to be less likely to reproduce must have a profound effect on the probability of its kin to survive in order for this 'back-door selection' to occur. Where are you getting this?

[/ QUOTE ]

Well, I "got" it from years of studying paleoanthropology in college and teaching genetics and evolutionary theory. Where do your ideas come from?

In order to make sense of altruism, we have to understand that it doesn't matter which of the examples of a specific gene survives, as long as it does. The source, which relative passes it on, becomes a matter of indifference. Once genes are deposited in the next generation, protecting that container, the individual with the genes inside, becomes the greatest driving force in behavior as long as production is constant. We don't think of the genome and how it evolves in terms of individuals, but in terms of populations. One of the most positive forces for selective fitness, is controlling the number of individuals in the population because production and reproduction are so intertwined as to be almost indistinguishable from one another.

[ QUOTE ]
[ QUOTE ]
Ejecting gay persons from our families and communities is counter to reproductive success for the population as a whole.

[/ QUOTE ]

Not anymore, by your own lights.

[/ QUOTE ]
I have no idea what this means.

[ QUOTE ]
I say ejecting gay persons from our families and communities is morally repugnant on the grounds of human liberty.

[/ QUOTE ]
I agree and say the same thing. But that isn't the topic of the thread.

[Praxising]

[ QUOTE ]
Living in human society has skewed your vision of what happens in the natural world. The majority of organisms born don't reproduce, huge amounts die between the fertilized egg -> reproductive egg stage. Since most animals don't live to reproduce the loss of one who loses all possibility only costs a fraction of what you might think, thus the beneficial effect doesn't have to be profound at all.

[/ QUOTE ]

Exactly! Great post.

[All-In Flynn]

[ QUOTE ]
Do you mean bonobo chimps?

[/ QUOTE ]

Pretty sure I do - cheers.