Game theory explanation for homosexuality?

[chabibi]

I was wondering if there have been any studies or theories published that use game theory to explain evolutionary reasons for homosexuality.

I was thinking somewhere along the lines of the Hawk-Dove game used to explain aggression in animals. As far as I know, most human populations have a pretty consistent homosexuality rate (I think they told us in high school something like 1 in 10) and this got me thinking that perhaps there is some sort of payoff to the species when a portion of the population engages in same sex relations.

Has anyone ever heard of something like this? And if not could you conceivably think of why it might pay off for a species?

[jason_t]

A species sole concern is the preservation of its genes. Being homosexual and not reproducing but instead caring for your siblings and their children acheives this goal since said relatives have a very similar genetic makeup.

It's much more complicated than that, and there are criticisms of this theory, but let's use it as a starting point.

[CallMeIshmael]

[ QUOTE ]
And if not could you conceivably think of why it might pay off for a species?

[/ QUOTE ]

Just to clarify: it is NEVER for the good of the species. When using evolution to explain a trait, it it always for the good of the indiviudal and not the good of the species.


Possible explanations for homosexuality:


1. Heterozygote advantage. Sickle cell anemia is prevalent in Africa because the heterozygote for the disease is malaria resistent, and thus more fit in that environment.

Now, of course something like homosexuality isnt going to be a simple one gene type thing, but a similar mechanism might be at work.


2. Inclusive fitness. If homosexuals are more likely to stay at home and help raise their brothers/sisters/neices/nephews etc, then they may increase their inclusive fitness this way, because the increased parental investment helps the survival chances of your kin.

(Note: inclusive fitness means that though you dont replicate, some of your genes replicate because your relatives share your genes. Also, there is a discount. Sibling/Parent = 0.5, nephew = 0.25, etc.)


3. Maternally inherited factors:

- same sex men have more homosexual relatives on their mothers side than fathers side
- maternal relatives of gay men have higher fercundity BUT the same is not true of straight men

This means that there might be a gay gene that promotes fercundity in women but homosexuality in men, and thus it stays in the population because the women pass it on


4. There is some evidence that the female immune system reacts badly to male pregnancies. Male antigens may be the cause.

The chances that a male is born gay significantly increases with every older brother he has, but is uncorrelated to older sisters. Also, there is no effect when the brothers did not share a womb.

[jason_t]

[ QUOTE ]
[00:16] jason_t: nice post
[00:16] CallMeIshmael: u and i both know
[00:16] CallMeIshmael: that that is my area
[00:16] jason_t: gayness? yes sir, i know

[/ QUOTE ]

[CallMeIshmael]

JT (3:16:21 AM): THANKS FOR SPENDING MORE TIME ON YOUR POST THAN I DID
CMI (3:16:30 AM): hahaha
JT (3:16:35 AM): nice post
CMI (3:16:37 AM): u and i both know
CMI (3:16:45 AM): that that is my area
JT (3:16:49 AM): yes sir
CMI (3:16:53 AM): and when i say that
CMI (3:16:56 AM): i dotn be gayness
CMI (3:17:01 AM): i mean evolution :-)
JT (3:17:20 AM): LOL"
JT (3:17:22 AM): LOL
JT (3:17:22 AM): LOL
CMI (3:17:26 AM): i just read that
CMI (3:17:28 AM): and i was like
CMI (3:17:29 AM): [censored]
JT (3:17:53 AM): this AIM conversation is so getting altered and posted
JT (3:17:56 AM): don't even think i won't


REAL conversation

[jason_t]

[ QUOTE ]
JT (3:16:21 AM): THANKS FOR SPENDING MORE TIME ON YOUR POST THAN I DID
CMI (3:16:30 AM): hahaha
JT (3:16:35 AM): nice post
CMI (3:16:37 AM): u and i both know
CMI (3:16:45 AM): that that is my area
JT (3:16:49 AM): yes sir
CMI (3:16:53 AM): and when i say that
CMI (3:16:56 AM): i dotn be gayness
CMI (3:17:01 AM): i mean evolution :-)
JT (3:17:20 AM): LOL"
JT (3:17:22 AM): LOL
JT (3:17:22 AM): LOL
CMI (3:17:26 AM): i just read that
CMI (3:17:28 AM): and i was like
CMI (3:17:29 AM): [censored]
JT (3:17:53 AM): this AIM conversation is so getting altered and posted
JT (3:17:56 AM): don't even think i won't


REAL conversation

[/ QUOTE ]

What I posted is the real conversation. Don't forget this (http://forumserver.twoplustwo.com/showflat.php?Cat=0&Number=5505763&an=0&page=0#Post 5505763).

[Hererdebert]

You can't talk about evolution in terms of the cumlative benefit for the entire species. Evolution only works on an individual basis, it is only the success of each individual 'gene machine' that is relevant and the transmission of successful, complementary genes that matters. Game theory is an extension of this, in that it explains the specific advantages accrued by an individual within a larger system (eg, how a stable balance is naturally reached between agression and passivity).

[chabibi]

[ QUOTE ]

Just to clarify: it is NEVER for the good of the species. When using evolution to explain a trait, it it always for the good of the indiviudal and not the good of the species.

[/ QUOTE ]

Of course I understand this, I made the post at 3 in the morning and it was just a brain fart, I apologize.

However, this only adds more confusion, because any genetic trait that places the good of the species over the good of the individual will not be passed down. So I don’t really see how your point system example would be in the best interest of the individual players, because they could always increase their own payoff by having offspring of their own.

[_Z_]

[ QUOTE ]
So I don’t really see how your point system example would be in the best interest of the individual players,

[/ QUOTE ]

Let's say there's a species of animal where a mother will care for its children, but won't risk her own life to save a child. Now say a gene shows up that makes it so the mother will take on some small risk to her own life to save a child from certain death.

Even though this gene will result in a slightly higher chance of early death for the mother, the gene will still be selected for since her child is 50% likely to have this gene and will have a much greater chance of survival.

Z

[luckyme]

[ QUOTE ]
Just to clarify: it is NEVER for the good of the species. When using evolution to explain a trait, it it always for the good of the indiviudal and not the good of the species.

[/ QUOTE ]

Essentially, the focus is on the gene line and not the current individual or the current pool of individuals, or the current individuals descendants.

Humans are modular beings, and it pays our species ( as the gene line carrier) to have a good method of mixing and matching a wide variety of traits, including those typically associated with gender identification. It's inevitable and desirable ( to the robustness of the gene pool) that individuals will turn out with non-standard gender identities.

Homosexuality of whatever degree isn't 'for' anything any more than heterosexuality is. Nothing is evolutionarily 'for' anything.

Sexes work for a species by increaseing diversity and avoiding cookie-cutter production issues. The end product is 'variety' of personality, sexuality, body size, shape, almost any aspect of being human.

Perhaps in Gould's view ( which isn't all wrong), homosexuality could be looked at as a special case of spandrel from 'maintaining variety'. It's just another way a human comes out in the big scheme of things.

luckyme

[CallMeIshmael]

Im not really sure what you're trying to say.

Are you saying that homosexuality exists because it gives variety to the species?

[luckyme]

[ QUOTE ]
Are you saying that homosexuality exists because it gives variety to the species?

[/ QUOTE ]

No, it's that way of looking at it ( the 'for' approach) that I'm trying to counter.

Homosexuality exists because the species has variety, because it is a modular mix-and-match process that creates each individual. My particular face is not 'for' anything, it's just one of the ways that face structure comes out in a mix-and-match reproductive system.

My brain structure, my gender structure is at least as modularily constructed, variety will be the outcome and in a sexual species is part of the reason they are successful ( that doesn't make it a 'goal').

hope that's clearer , luckyme

[hmkpoker]

well.

Considering our population, I think it's safe to say that homosexuality is no threat to reproductive success.

[luckyme]

[ QUOTE ]
Considering our population, I think it's safe to say that homosexuality is no threat to reproductive success.

[/ QUOTE ]

It may well be key to understanding our reproductive success. Homosexuality aside, a species that is considered the most adaptable in the history of the planet is a species that thrives on 'variety'. Somebody has to like blonds, raspy voices, men over 7 ft, mesomorphs, you name it.

Throw in our bobono level of horniness ( another species that has even more homosexuality than we do) and you're going to have a species that is aroused by a variety of attributes, sometimes inflatables will do. That some attraction will be what we term 'homosexual' ( as if it were a uniform state) seems only natural and predictable in a species that built it's success on it's variety and adaptability.

luckyme

[CallMeIshmael]

I disagree with what you're saying.

Again, Im still not 100% on what it is you're arguing, but it seems that you are arguing that since we are a sexual species, we have diversity (true), and that diversity alone can explain homosexuality (not true).



[ QUOTE ]
Homosexuality exists because the species has variety, because it is a modular mix-and-match process that creates each individual. My particular face is not 'for' anything, it's just one of the ways that face structure comes out in a mix-and-match reproductive system.

[/ QUOTE ]

Your face is most certainly 'for' something. It not only serves its obvious functions, but it is the result of sexual selection. Though there is clear variation, there are things about the human face that remains constant through populations around the world, and these traits dont vary because memebers of the opposite sex dont find them attractive or they have fitness costs to the person (sexual selection is more important on things like the face)

[ QUOTE ]
My brain structure, my gender structure is at least as modularily constructed, variety will be the outcome and in a sexual species is part of the reason they are successful ( that doesn't make it a 'goal').

[/ QUOTE ]


A trait that is common to such a large portion of the population, and one that so clearly has a negative effect on the person's probability of propagating is very likely the result of other fitness benefits that we may not know, and not simply random variation in the population.

[CallMeIshmael]

[ QUOTE ]
Considering our population, I think it's safe to say that homosexuality is no threat to reproductive success.

[/ QUOTE ]

It certainly is to the individual.

[morphball]

[ QUOTE ]
Just to clarify: it is NEVER for the good of the species. When using evolution to explain a trait, it it always for the good of the indiviudal and not the good of the species.


[/ QUOTE ]

I disagree with this completely. Ants evolved where the vast majority of them do not reproduce sexually, so do bees and termites. Yet these species are incredibly adept at adapting to their environment.

Ants and such are pretty interesting, because you could make the argument that one colony consists of one individual, and the all the worker ants, etc, are just different cells. Who knows.

[CallMeIshmael]

[ QUOTE ]
[ QUOTE ]
Just to clarify: it is NEVER for the good of the species. When using evolution to explain a trait, it it always for the good of the indiviudal and not the good of the species.


[/ QUOTE ]

I disagree with this completely. Ants evolved where the vast majority of them do not reproduce sexually, so do bees and termites. Yet these species are incredibly adept at adapting to their environment.

Ants and such are pretty interesting, because you could make the argument that one colony consists of one individual, and the all the worker ants, etc, are just different cells. Who knows.

[/ QUOTE ]


I technically mispoke. When I said 'individual' I actually meant 'Genes of the individual'.

Evolution acts on genes.


The evoltion of eusociality (that which you described) can be explained from the perspective of the gene.

The fact that some bees/termites dont mate is made up for by the fact that their genes are being propagated by others.

[luckyme]

[ QUOTE ]
Again, Im still not 100% on what it is you're arguing, but it seems that you are arguing that since we are a sexual species, we have diversity (true), and that diversity alone can explain homosexuality (not true).

[/ QUOTE ]

Definitely not true :-)
[ QUOTE ]
A trait that is common to such a large portion of the population, and one that so clearly has a negative effect on the person's probability of propagating is very likely the result of other fitness benefits that we may not know, and not simply random variation in the population.

[/ QUOTE ]


Evolution cares dick-all about any individuals reproductive success. Looking at evolution at 'individual based' level will make my statements mean nothing to you. In order to evaluate them, whether you agree or not, you'll need to see that most of my argument exists above and below the level of the individual.

Sometimes there is confusion caused by the cultural side of sexuality and the innate horniness of the species. Using only the 'role' view of explaining traits, I couldn't explain Prince Charles ears, or Wilt Chamberlains height, or flaming red hair, or why I'm not attracted to blonde's or... well, almost anything specific.

It's not the persons reproductive 'fitness' that is being tested by evolution, it is the fitness of the 'system' used by the genes to propagate themselves. If it worked best that every male pee'd on every tree stump or ejaculated into every available crevice ( ok, ok, I think I know a few that have both those traits) then there's a good chance that's how we'd end up ( there are constraints).

There are lots of other factors, but here are some to consider - We don't eat sugar and fat because we have a genetically driven desire to be 400 lbs. We evolved a desire for sugar because it worked !, to the benefit of the species/genes. Well, we're attracted to the pleasure of sex and lured on by smells, sights of cleavage, signs of wealth, shapes of hips, lips, "whatever turns your crank" .. there are a lot of crank turners out there.

There may well be social-level reasons that support homosexuality in an evolutionary sense, male-bonding, super-cross-grooming and such. Since sexual pleasure is the real 'goal' ( because it tends to produce more successful genes by it's satisfacton), it can be co-opted at the actual social level for other uses. It's just as hard to explain condoms and sex by 60 year old women, if 'offspring' was the actual goal of sex.

The variety issue arises because of the modular way we seem to be structured., and there's likely as many forms of 'homosexuality' as there are homosexuals. ( It's like the uni-atheist view that most believers have of them.). If we chopped a person into 100’s of modules and recombined them within constraints that we don’t have too many two-headed ones, you’re going to end up with attraction to big hairy chests hooked to a penis-bearing frame. Unless such a configuration feeds direct harm into the gene pool, and if such a configuration is socially co-opted for other functions ( I’ve mentiond a couple), then we’ll see that variety continue. The ‘pool’ requires a lot of flexibility in it’s modularity and the amount of constraint required to eliminate homosexuality obviously hasn’t been found to be worth it to the genes. So, even if homosexuality was -EV to the pool on it’s own ( and we have no reason to think it is), it may perpetuate because the co-opted functions it performs contribute to overall success of the pool and/or it’s not worth the cost of getting rid of it for creative mix-match reasons.

We know it’s not as simple as we can write it out,
but I hope that’s a clearer explanation of what I was pointing to, luckyme

[CallMeIshmael]

[ QUOTE ]
Using only the 'role' view of explaining traits, I couldn't explain Prince Charles ears, or Wilt Chamberlains height, or flaming red hair, or why I'm not attracted to blonde's or... well, almost anything specific

[/ QUOTE ]

Just to point out: there is a HUGE difference between's someone's height and someone not being attracted to the opposite sex.

Its unlikely that someone being fairly tall, or having bigger ears, greatly reduces their fitness to the point of not being able to propagate. This is not true of homosexuality.

[ QUOTE ]
We don't eat sugar and fat because we have a genetically driven desire to be 400 lbs. We evolved a desire for sugar because it worked !, to the benefit of the species/genes.

[/ QUOTE ]

What do you mean when you say species? Evolution doesnt act on the species level.



Also, to be honest, Im not even sure what you disagree with, from my points:

1. Homosexuals tend to not reproduce / reproduce less
2. Therefore, their genes are less likely to reproduce
3. Since homosexuality is still prevalent, it is likely that homosexuality is tied to some other element of increased inclusive fitness.


Where do we disagree?


EDIT: also,

[ QUOTE ]
It's not the persons reproductive 'fitness' that is being tested by evolution, it is the fitness of the 'system' used by the genes to propagate themselves.

[/ QUOTE ]

Reproductive fitness is defined as your success of passing genes on to the next generation. This IS what evolution acts on.

[oneeye13]

[ QUOTE ]

Just to clarify: it is NEVER for the good of the species. When using evolution to explain a trait, it it always for the good of the indiviudal and not the good of the species.


[/ QUOTE ]

this "clarification" is remarkably powerful in its explanation of the worker ant

[CallMeIshmael]

[ QUOTE ]
[ QUOTE ]

Just to clarify: it is NEVER for the good of the species. When using evolution to explain a trait, it it always for the good of the indiviudal and not the good of the species.


[/ QUOTE ]

this "clarification" is remarkably powerful in its explanation of the worker ant

[/ QUOTE ]

Pls read the thread

[luckyme]

[ QUOTE ]
Where do we disagree?

[/ QUOTE ]
[ QUOTE ]
Reproductive fitness is defined as your success of passing genes on to the next generation. This IS what evolution acts on.

[/ QUOTE ]

It's true that MY reproductive fitness refers to my personal reproductive success, but evolution operates in the interaction of gene combinations over generations. After all, "I" don't evolve nor, essentially, do individual genes. Evolution doesn't care about my personal success, nor about the personal reproductive success of my homosexual neighbour. It operates on the overall success of all it's 'kin'.

There are lots of ways and reasons that homosexuality would appear in a 'bisexual' species (accepting the misnomer), and none of them require any homosexual person to have a child to 'pass on their genes'.

A species could easily produce 'nanny' phenotypes ( not that I think that is the valid in the case of homosexuals) without ever a nanny having an offspring. You seem very aware of that, so I'm having trouble with ...

[ QUOTE ]
1. Homosexuals tend to not reproduce / reproduce less
2. Therefore, their genes are less likely to reproduce
3. Since homosexuality is still prevalent, it is likely that homosexuality is tied to some other element of increased inclusive fitness.

[/ QUOTE ]

specically, I don't see how 1 and 3 lead to 2. If 3 is valid ( and my claim is that an expanded inclusive fitness concept is true) then 'their genes' are passed on by their neighbours. "Their genes" doesn't, or at least it shouldn't, refer to their personal supply of genes, but to 'genes that produce homosexuals'.

maybe that focuses the issue I'm trying to clear up better, thanks for the comments, luckyme

[oneeye13]

[ QUOTE ]
The fact that some bees/termites dont mate is made up for by the fact that their genes are being propagated by others.

[/ QUOTE ]

i like how this statement only applies to the species you want it to. seems funny to me that you would consider yourself an expert on this subject.

[CallMeIshmael]

[ QUOTE ]
i like how this statement only applies to the species you want it to. seems funny to me that you would consider yourself an expert on this subject.

[/ QUOTE ]

Ummm... ok, if I made that ants/bees/termites would you be happy?... because if you go here (http://en.wikipedia.org/wiki/Eusociality) they're all mentioned as examples of eusociality

(im assuming you mean ants, because that was your grand revelation from before, but maybe you meant something else)


No, I dont consider myself an expert on this subject. BUT, I am in my fourth year of a bio degree, with this subject as my concentration. And, I will be getting a phD in ethology, so I have some knowledge here. But, Im sure you have much to teach me.


EDIT: While we're here, this (http://en.wikipedia.org/wiki/Kin_selection) might help

[CallMeIshmael]

[ QUOTE ]
[ QUOTE ]
1. Homosexuals tend to not reproduce / reproduce less
2. Therefore, their genes are less likely to reproduce
3. Since homosexuality is still prevalent, it is likely that homosexuality is tied to some other element of increased inclusive fitness.

[/ QUOTE ]

specically, I don't see how 1 and 3 lead to 2. If 3 is valid ( and my claim is that an expanded inclusive fitness concept is true) then 'their genes' are passed on by their neighbours. "Their genes" doesn't, or at least it shouldn't, refer to their personal supply of genes, but to 'genes that produce homosexuals'.

maybe that focuses the issue I'm trying to clear up better, thanks for the comments, luckyme

[/ QUOTE ]


OHH... there we go, I think this is all cleared up. This was a miscommunication.

What I meant by 2 was, their genes are less likely to be *directly* passed on. Ie. have kids themselves.

BUT, since it is still an observed trait, there must be indirect fitness benefits.

[luckyme]

[ QUOTE ]

[ QUOTE ]
It's not the persons reproductive 'fitness' that is being tested by evolution, it is the fitness of the 'system' used by the genes to propagate themselves.

[/ QUOTE ]

Reproductive fitness is defined as your success of passing genes on to the next generation. This IS what evolution acts on.

[/ QUOTE ]

I've always found it interesting just what it is that people think is evolving. Some of the Dawkins camp vs Gould camp that touches this topic is an enjoyable look at a diverse ways of seeing the same thing. Essentially I'm with Dawkins, but Gould made some solid points.(ignoring his ego-romp into punctuated equilibrium)

luckyme

[luckyme]

[ QUOTE ]
What I meant by 2 was, their genes are less likely to be *directly* passed on. Ie. have kids themselves. BUT, since it is still an observed trait, there must be indirect fitness benefits.

[/ QUOTE ]

I rather suspected we weren't in trouble there, but I'm such a terrible explainer I tend to assume it's my side of the net.

I'm not sold on the "indirect fitness benefits" being mandatory,or at least primary, although I can conjure up some possibilities. Modularity of traits likely has a finger in there, maybe a whole hand. There is no reason why sexual traits need to be considered any differently than personality or even physical traits.

luckyme

[Marko Schmarko]

Seems to me that it might be a byproduct of the hyper-sexual nature that is so adaptive generally.

This would only seem to suggest bisexuality, however.

To Bonobos have "pure", life-long homosexuals?

Maybe there are some higher-level psychological factors at work.

[luckyme]

[ QUOTE ]
Seems to me that it might be a byproduct of the hyper-sexual nature that is so adaptive generally.

[/ QUOTE ]

I think that has to play a fair-sized part in it.
[ QUOTE ]
Maybe there are some higher-level psychological factors at work.

[/ QUOTE ]

If you mean things like -not every penis-bearer can be an alfa-wanna-be, and the mix in the group that gives rise to different personalities (see the "what would you have accomplished? thread) could well play out as the occassional homosexual. So, it may not be that homosexuality is 'needed', but the range of personalities that a successful tribe contains happens to be easy to attain with homosexuality as one of the options.

That was an aspect of the 'variety' tendency I suggested could contribute to it.

bonobo's, I understand they're an 'every crevice needs probing' type, but there seems some useful social issues that homosexuality addresses for them ( to early to say if similar for us).

luckyme

[morphball]

Some one found this article in another post, and part of it was very fitting for this thread...

natural selection among competing groups of individuals (http://www.newyorker.com/printables/critics/060403crbo_books)

[ QUOTE ]
According to Wilson, though, evolution sometimes involves natural selection among competing groups of individuals. Consider “predator inspection” in guppies. If a potential predator approaches a school of guppies, one or two fish may peel away from the group, inspect the intruder, and then (if their luck holds) return to the school, reporting on the danger. Predator inspection is paradoxical. Why would a guppy take on such a risky assignment? Why be an altruist? Group selection provides a possible answer. Predator inspection might evolve not because inspectors leave more progeny than non-inspectors within a group—traditional individual selection—but because groups that include inspectors survive better than groups that don’t. Although Wilson doesn’t think that all evolution involves group selection, he thinks that group selection plays a big enough role that a realistic theory of evolution must allow for both individual and group selection.

[/ QUOTE ]

[CallMeIshmael]

[ QUOTE ]
Some one found this article in another post, and part of it was very fitting for this thread...

natural selection among competing groups of individuals (http://www.newyorker.com/printables/critics/060403crbo_books)

[ QUOTE ]
According to Wilson, though, evolution sometimes involves natural selection among competing groups of individuals. Consider “predator inspection” in guppies. If a potential predator approaches a school of guppies, one or two fish may peel away from the group, inspect the intruder, and then (if their luck holds) return to the school, reporting on the danger. Predator inspection is paradoxical. Why would a guppy take on such a risky assignment? Why be an altruist? Group selection provides a possible answer. Predator inspection might evolve not because inspectors leave more progeny than non-inspectors within a group—traditional individual selection—but because groups that include inspectors survive better than groups that don’t. Although Wilson doesn’t think that all evolution involves group selection, he thinks that group selection plays a big enough role that a realistic theory of evolution must allow for both individual and group selection.

[/ QUOTE ]

[/ QUOTE ]


FWIW, in several species that display this behaviour, there is a correlation between altrusim and attractiveness.

That is, the males that go out and look for predators are found to be more attractive to females (looking for predators is going to be an honest signal of good genes), and thus IF they make it back, will pass on more offspring than non-lookers.

There are still a few things that group theory is used to explain, because selfish-gene doesnt fully explain it yet. But, for most evolutionists, using group theory is a no-no (at least that is what Ive been taught). For the most part, everything can be done with selfish gene.


EDIT: Also, of course, there is reciprocity. That is, if one fish looks, then another will look instead the next time to pay him back. Both fish are more fit now than if neither had looked in the first place, but, once again, it is all explained from looking at each indivudals choices, and not those of the group.

[Rduke55]

[ QUOTE ]
So I don’t really see how your point system example would be in the best interest of the individual players, because they could always increase their own payoff by having offspring of their own.

[/ QUOTE ]

No, because selection happens at the level of the gene. A gene that makes more copies of itself - whether by the organism directly reproducing or through reproduction-by-proxy will beat out a gene that makes less copies of itself, even if it's through direct reprodcution.

Kin relationships here are all important. So relatives share a percentage of genes. If you help your relative reproduce, since he or she shares the same genes as you you're passing some of the same genes to the next generation.

You can do math with this (evolution of cooperative behavior is full of this). In some situations you can pass more of "your" genes by giving up your own reproduction.

Look at two groups of two sisters. One group only does direct reproduction and, due to the availablility of resources, predation, etc. each animal loses 80% of it's offspring/year.
With the other couple, only one animal reproduces and produces the same amount of offspring but the other helps provide for the offspring in lieu of having its own offspring so they only lose 20%.
Let's say that each animal can have a litter of 10 once a year. In the first group each animal has 10 offspring of which 2 survive. Each animal shares 50% of their genes with direct offpring and 25% with neices/nephews. So convert all of those to decimals and add them up to determine the total amount of genes in the next generation.
2 offpring each with 0.50 relatedness = 1
2 neices each with 0.25 relatedness = 0.5
So in the first example for each animal we'll give a number of 1.5.

In the 2nd example only one sister has kids and 8 of those survive so it's obvious that there's a huge benefit for her there.
But what about the other animal that's not reproducing? If she receives no benefit then it doesn't make sense.
But...
She has 0 offspring with 0.50 relatedness = 0.
And 8 neices with 0.25 relatedness = 2

So in this case 2>1.5 so she actually gets more of her genes into the next generation by forgoing her own reproduction.

[chabibi]

[ QUOTE ]
Look at two groups of two sisters. One group only does direct reproduction and, due to the availablility of resources, predation, etc. each animal loses 80% of it's offspring/year.
With the other couple, only one animal reproduces and produces the same amount of offspring but the other helps provide for the offspring in lieu of having its own offspring so they only lose 20%.
Let's say that each animal can have a litter of 10 once a year. In the first group each animal has 10 offspring of which 2 survive. Each animal shares 50% of their genes with direct offpring and 25% with neices/nephews. So convert all of those to decimals and add them up to determine the total amount of genes in the next generation.
2 offpring each with 0.50 relatedness = 1
2 neices each with 0.25 relatedness = 0.5
So in the first example for each animal we'll give a number of 1.5.

In the 2nd example only one sister has kids and 8 of those survive so it's obvious that there's a huge benefit for her there.
But what about the other animal that's not reproducing? If she receives no benefit then it doesn't make sense.
But...
She has 0 offspring with 0.50 relatedness = 0.
And 8 neices with 0.25 relatedness = 2

So in this case 2>1.5 so she actually gets more of her genes into the next generation by forgoing her own reproduction.

[/ QUOTE ]

This is exactly the type of example I was looking for. Thank you