MyKell

First of all, you are changing your argument from having the individual as the selection unit, to that having genetically similar individuals.
Second of all, current models that predict altruistic behavior based solely on genetic relatedness fail to predict why this behavior is no different among genetically distinct siblings than that among identical twin siblings.
A cat is more likely to defend its babies, who are 50% identical in genetic material much more readily than its identical twin which is a 100% identical.
Thirdly, altruistic behavior is established within human communities without the need to invoke genetic relatedness. Heard of mother teresa?

scigirl

[boring science hat on]

I'm not sure if this was pointed out yet but - does anyone have data proving that homosexuals actually produced less offspring? It's entirely possible that due to cultural or other factors, in the ancestral environment, people with homosexual tendencies still produced the same amount of offspring as heterosexuals.

I agree with Didymus on this issue - first we need to know the gene or genes responsible for homosexual behavior (we don't), and second we need to know how they affect the fitness of the individual (we don't know that either).

[/boring science hat on]


But - all this speculation makes for cool discussion anyway. . .

scigirl

pz

I'm invisible! That was the main point of my first and second post in this thread. No, we have no such data.

scigirl

pz - I noticed that! I posted before I read through the whole thing!

scigirl

pz

I'm not changing any argument. I'm saying that if you want to argue that homosexuality is hereditary (which I do not believe) and that it confers some group advantage (which I do not), the homosexual trait isn't going to experience a selective advantage unless it promotes the well-being of a related group.I'm not a big fan of sociobiological models of altruism, so I agree. There are problems. However, the idea that a heritable trait might have a selective advantage if it promotes the well-being of individuals who do not have the trait has even more problems.Well, this situation actually doesn't seem like that big of a dilemma to me, but I'm not married to the "degree of relatedness is all that matters!" mob. It's more of a game theoretic, investment strategy kind of problem.

Although it could be easily resolved in the altruism model, too, it seems to me. Ferocity in defense of one's young would be a useful trait not only for the mother, but for the mother's sisters. Sacrificing one's self for one's sister is only going to be useful if you know she is going to defend your nieces and nephews.Yes. She's not an example of biological altruism, though, and I don't think anyone has argued that her behavior was a heritable trait.

It's not such a great example of human selflessness, either, since I think she was a self-centered, ignorant old hag with serious mental problems.

MyKell

I'm not arguing that homosexuality is hereditary. I thought I made clear that I support a view that it is developmental. Behavior per se is far more complex than to be explained by genes alone, at least a behavior as complex as homo/heterosexuality.


Don't know how that relates? I'm not following

Ok well mother teresa was just an example. What I was trying to get to is the whole altruistic behavior that people seem to show that would not correlate with genetic relatedness. Now I didn't say that this was heritable and neither did I say that homosexuality was heritable. I was just trying to point out why it offers an evolutionary advantage on a group level.

Baloo

(editted to add, for pz's and scigirl's sake: "ASSUMING A NEGATIVE CORRELATION BETWEEN HOMOSEXUALITY AND REPRODUCTIVE FITNESS",)

(editted to reword a wordy sentence)

I tend to side with the selfish side of this debate. That is - only things which aid an individual's genetic reproductive success will be selected for.

On homosexuality:
I do not find plausible the idea that homo sapien ancestors, with a reproductive capacity of 10 or so, could have any net survival advantage in producing one homosexual offspring amongst 9 heterosexual offspring. There is a lot of hypothesizing about the potential advantages of this setup - but no ironclad case has been made that there would *always* be an advantage.

However, there would *always* be a disadvantage: if I have 9 breeding children and one non-breeder, my 9 breeeders will have to compete with the non-breeder for resources (well before they even reach a stage where sexuality makes a difference). Thus, they are less likely to survive to a breeding age than if I had simply had 9 breeders, period. Quite simply, my breeding offspring will be harmed by a reduction of resources available to them, and will be less likely to pass on the genes I gave to them. The concreteness of this fact just seems to make the "gay uncle" counter-hypothesis (or any other I've yet heard) pale in plausibility. IMO of course.

So, why do I think it is here? 2 scenarios:

1) Perhaps it is much cheaper to genetically code and develop a "loose cannon" sexual drive, which generally points the sexual drive of males towards females (and vice versa), than it is to genetically code a precise "sniper rifle" sexual drive. IOW, a cannon that hits it's target 98% of the time, but is much cheaper to build may simply be selected preferably to the resource intenive construction of a sniper rifle (even though the sniper rifle might work at 99.9%).

2) -more likely - Perhaps in the analogy above, the sniper rifle *is* the most preferable design. However, no evolutionary pathway existed to such a sniper rifle. In very loose terms, a long time ago, genetic ancestors of ours could either develop a primitive-cannon approach to a sexual drive, or a primitive-rifle approach. The primitive-cannon *was* better than the primitive rifle, thus that path was taken, and no switchback presented itself thereafter. IOW, perhaps homosexuality simply belongs as one more entry on the sub-optimal desing page...


On Altruism/unselfishness: 2 scenarios:
1) Homo sapiens are social. Selfishly, it is both in our reproductive and survival advantage to be surrounded by "self-sacrificers". Thus, we are very well served to befriend and accept others who act in a self-sacrificial, unselfish manner. On the flipside of the coin, it is better to be accepted by a society than be rejected by a society. From the above two points, a person who behaves in a self-sacrificing manner is more likely to be socially acceptable. I'd argue that in the majority of cases, the cost of being unselfish is far cheaper than the cost of being rejected by one's society (in ancestral times, the equivalent of genetic suicide). Thus, a general "give your resources to others" genetic encoding would be selected for (in constant conflict, of course, with a similar general "survive and reproduce at all costs" encoded rule).

2) Especially in primitive societies, human adults in a position to give up their life to save or protect others have a high statistically likelihood to be doing so for the protection of their own progeny. The coding of the behavior "die for others" is generally prevelant in adults. For an adult that has already had children (and may be past reprodcutive age), it is better for that adult's genes if the adult him/herself dies in place of the adult's child(ren). Thus, altruism for adults as a general rule may be advantageous to the genes which accompany it. Keep in mind, only very general impulses can be encoded for - which serve the role of greatly influencing our decision-making rational, but do not themselves make for a rational argument.


My .02.

-Baloo

aach

Just thinking that the idea of Homosexuality being derived from uterinal changes brought on by stress could well result in better survival chances of the womans other children. A homosexual son would not compete against the other kids and in situations where resources were scarce that would be a distinct advantage to the mothers genes.

My original thinking about this issue was that homosexuality could be a positive traite allowing a youngster to survive against an aggresive dominant male (would pose no threat). Survival results in opportunities to procreate especialy if the dominant male treated the homosexual as a female (while the desire may not exist in the homosexual it could exist in a female and sexuality is not so clear cut as to preclude procreation).

It seems to me that there is no clear answer to this question. The Evolutionary purpose of homosexuality is probably very complex, involving both social and environmental neuances.

Nic Tamzek

For the record, I doubt:

1) The 10% figure
2) The clear distinction assumed here between "hetero" and "homo"
3) That sexuality in the modern western cultural/environmental context has much at all to do with understanding how sexuality evolved in our stone age ancestors
4) That whatever hypothetical genetic trait hypothetically causes/biases sexuality towards the homosexual end of the spectrum would in fact have decreased sexual reproduction in our stone age ancestors. Someone cited a bunch of animals that have had homosexual behavior observed, but how many of those critters never engaged in heterosexual behavior at some point in their life cycle?

...and I see not much evidence supporting things would be predicted on various hypotheses, e.g., that homosexuals/heterosexuals are more/less helpful to the family.

As I think I pointed out the last time this topic came up at II, there are an awful lots of things that could tweak things a few percent in a species, particularly a species in our decidedly non-original state. I mean, what percentage of women turn out to be sterile, or would die during first childbirth without modern medicine? I wouldn't be surprised if it were a few percent (at least). Does this then require us to take seriously the hypothesis that natural selection favored this non-reproductive "trait" for some reason? No, it is just a by-product of other factors.

...in the spirit of Scigirl's boring scientist cap...
nic

Doubting Didymus

It seems we have something of a consensus. Hypotheses that paint homosexuality as an adaptation, though not theoretically impossible, suffer gravely from a lack of hard evidence that demonstrates any of a variety of predictions that that hypothesis should make. These holes include:

1: A lack of evidence that homosexuality is genetic (or simply, 'heritable', for those of us here who are not gene centrists).

2: A lack of evidence that homosexuality significantly impairs reproductive success.

3: For those hypothesis that rely on homosexuals as 'sterile helpers' (such as my own hypothesis, which I do not actually advocate), a lack of evidence that homosexuals in a human family setting benifits the relatives more than the drain on resources that any individual represents.

4: Theoretical problems exist for those hypotheses that have homosexuality as a population control device. Natural selection, (the only mechanism by which adaptations arise), can not favour traits unless the trait increases its own replication prospects. Altruism is one such trait, sterility is not.

5: A problem that always sticks strongly in my mind in these discussions: Why homosexuality? Why not sterility? Sterility is not hard to come by. It is one of the most common effects of deleterious mutations, so why would homosexuals evolve to fill the 'helpful non-breeder' and 'population limiter' roles, instead of sterile individuals?

All these problems, however, are small in comparison to the major problem I have with adaptationist hypotheses of homosexuality, which is simply that an alternative explaination exists that is much less problem fraught. Homosexuality is not a beneficial adaptation, but a non-heritable side effect of development. This hypothesis allows for homosexuality to be a neutral or even a NEGATIVE trait, as natural selection can only work on heritable features. In other words, the question 'why hasn't natural selection eliminated homosexuality, which is a detriment to the individual?' can be answered not by saying: 'perhaps homosexuality is not a detriment at all, I have this theory..." but by saying: "natural selection simply can not get at it, as it is not heritable".

There is often a desire for those of us with liberal minds to avoid having to paint this or that well known trait as a "bad" trait. None of us wants to feed the trolls. However, it is important to keep in mind that "bad" for natural selection should not mean "bad" to us as humans. We do not round up people with low sperm counts, hang them on barbed wire fences and then picket their funerals. We should not be concerned about labeling a trait as negative or neutral, as it is only in the minds of lunatics and idiots that natural 'is' equals human 'ought'.