What is the evolutionary advantage of homosexuality?

Factual Questions
41

I have to say I find your post equally baffling.

You know better than that. You’ve been around here long enough to know that you can’t pose questions, and then not expect others to comment on them, no matter what restrictions you try to place on them.

Could you please explain what the actual point of your questions were, then? You said:

This implies to me that you think this is some kind of unusual question. In fact, the OP stated in non-technical terms two quite reasonable possible hypotheses for the persistence of homosexuality in the population: 1) That homosexuals actually do succeed in breeding often enough to keep the trait in the population; and 2) the trait is maintained through group selection/kin selection.

Regarding your first question,

The OP’s second hypothesis actually is rather close to the traditional explanation for the fact that most members of a social insect colony don’t reproduce, that is, altruism due to kin selection, although the way it’s stated is more like group selection.

Regarding your second question,

The OP’s first hypothesis very clearly indicated he was aware that homosexuals are able to breed, therefore I am puzzled by why you would even ask this question.

Let me ask you some questions.

  1. Do you find the fact that someone would ask such a question unusual? Do you think the question is based on some kind of fundamental misunderstanding of biology?

  2. If so, why?

42

I notice that most of the reasons given are for male homosexuality.

I am clueless in this issue. Are male homosexuals more common than female homosexuals?

43

It’s almost impossible to really answer that with any accuracy due to a very wide array of problems (how do you define homosexual [e.g. is a person who has exclusively same sex fantasies but exclusively heterosexual intercourse gay or straight?]? how honest are the people polled? etc.). Statistics have not been taken on the matter for very long, either.

In the 2000 Census there were 1,202,418 people who self-identified as gay domestic partnership. (There were no single gays/lesbians counted as the question is considered an invasion of privacy except as applies to the living situation.) Of those the slim majority (304,148 couples, to be precise) were male-male, which would imply (but most certainly not prove) that there are probably more openly gay males than there are gay females.

44

Colibri:

  1. Reread my post.

  2. Reread my post.

  3. Reread my post.

Here is an analogy:

You are present when a manager is interviewing a job applicant. The manager asks the applicant “Do you know how a Spacely Sprocket SMDB-5000 works?”

You jump in because the manager “misunderstands” something and answer the question.

Note that:

a. The manager was asking the applicant not you.

b. The manager already knows how the Spacely Sprocket SMDB-5000 works. So you are just “flapping your jaws for light” as they say.

My post in no way shape or form contains a “misunderstanding”. None, zip, zero.

Please, in the future, read the post before replying.

Again, you are getting further and further away from the ballpark here. Stop and think.

45

This is a good excuse for a small essay on how evolution works (and how it doesn’t). I want to explain why it is a mistake to think that there is or could be a gene “for” homosexuality or, for that matter, blue eyes or type A blood.

To begin with, there is always an environmental component to anything. Even the studies of identical twins separated at birth suffer from the fact that they spent the first nine months of their existence in an environment that share many features. For example, it is known that among pigs, who produce litters of several piglets, even the position in the womb has its effect on the piglet. A male that lies in the womb between two females has, on average, a different porcinality that one that lay between two males. Who knows what effect even minor differences in the womb can have? It is at least conceivable that gayness is determined at least partly by events in the womb. Of course, that only puts the question back one stage: why doesn’t evolution eliminate females more likely to have gay offspring? One possible answer is that what works for females doesn’t for males and vice versa.

A gene codes for manufacturing one or more proteins. There used to be a doctrine one gene/one protein, but it is now understood that that is oversimplified. So there could well be a protein that, however it works, increases the likelihood of homosexuality, but also increases fitness in some other way. After all, homosexuals can and do have children. Not the males who “marry” other males young and keep their genes out of the gene pool, but that is a relatively recent phenomenon. Until a couple decades ago, most gays stayed in the closet and tried to maintain as normal a lifestyle as possible. Even now, lesbians often do have natural children, using artificial insemination or otherwise. (For an amusing example of otherwise, see the film Antonia’s Line. It was just one minor scene but I thought it was hilarious.) Anyway, the bottom line seems to be that genetics is such a hack that “You can’t do just one thing” is its motto. That is one difference between random design and intelligent design.

Here is another illustration of the same point. Most of you know that Stephen J. Gould wrote 30 years of monthly columns for Natural History (an extraordinary achievement just to write 360 columns) and these were collected into books of essays. One of them is titled The Panda’s Thumb and begins the essay of the same title. The title is usually assumed to refer to the panda’s forethumb, which is an extra thumb that is homologous to a wrist bone and is used to strip bark from bamboo, the panda’s only food. So far, a familiar type of evolutionary story in the “Just so” mode and not entirely convincing (the thumb could have evolved for some entirely different purpose and been converted to being a bamboo stripper). But at the end of the essay Gould reveals another fact that is, I think the real point of the essay: the panda also has an extra thumb on its rear foot, one that has no apparent purpose or function. I believe that that rear thumb is the thumb of the title. It is an introduction to one of Gould’s favorite topics, spandrel. “Spandrel” is an architectural term for a feature whose only purpose is to be a transition between two intentional features. An example is a transitional panel between a dome and a flat wall in a cathedral. It is often decorated, but decoration is not its primary function.

Another example of how evolution works in mysterious (and unintelligent) ways is sickle cell anemia. Until modern medicine came along I don’t think sufferers of SCA lived long enough to reproduce. It remains uncurable, but there are ameliorative treatments nowadays. How did such a debilitative disease remain at the level it is at? It turns out that its distribution largely parallels the distribution of malaria. This must take into account ancestral homeland, obviously. People who have one SCA gene do not have the disease, but they do have partial protection from malaria. The bacteria do not do well in blood cells that have one SCA gene (and those people do have mild SCA symptoms) and this apparently keeps the gene current in those populations.

46

The analogy fails completely because you are not the manager. You are only one poster among thousands. There is no evidence so far that you know much more than the OP about the subject.

This is not at all evident from your post. Perhaps you should provide what you believe to be the “'correct” answers to the questions you posed, so we may determine that.

It appeared from your questions that you yourself had not read the OP carefully, since the answer to one of the questions you asked was clearly contained within it. You might take your own advice.

Let us pretend that I am on the company staff and am interviewing you for a managerial position. :wink:

47

The problem is now clear-- you think you’re a manager of this thread.

I have to agree with **Colibri **on this. You can’t decide who does and who does not answer your posts. Besides, the OP seems to have abadonded his/her thread anyway.

BTW, I also agree that your questions strongly implied some hidden agenda on the OP’s part, which I don’t think is there.

48

In regard to the sub-thread on the comparative amounts of conflict within species, bonobos, chimps, humans, etc. It seems to me that the comparisons are not apt because the types of conflict that are being compared are physical confrontations. But bonobos and chimps can only resort to those types of conflicts because they do not have language. Humans, on the other hand, do have language, and because of this, can, and most certainly do resort to a different type of conflict, and I’d suggest that there most certainly is an enormous amount of intra-group conflict. No, we don’t have fist fights, but I’m sure that what passes for commerce in the board rooms in America is the “civilized” version of same. I think the conversation needs to be recast with some new definitions in order to recalibrate the argument. xo, C.

49

CC: Youre point is well taken, and I considered bringing that up earlier but didn’t want to sideline this thread too much. Instead, if you notice, I snuck a “physical” in front of my last reference to conflict. :slight_smile: Still, bonobos and chimps are just as capable of displaying their anger with vocalizations and body language as we are with speach. We might be able to put more nuance into it, but the message is clear in either of the 3 species.

50

Kinsey (1948, 1953) found male homosexual behavior to be much more common than female homosexual behavior. More here.

51

Kinsey’s sampling method was questionable, at best, so I don’t think his results are considered accurate these days. Iv’e seen data all over the place, often reflecting the political agend of the collector. I believe most scientists accept a number of about 5% for men, and somewhat lower for women. On this very personal subject with its associated social taboos, it should come as no surprise that accurate data is hard to gather.

52

There probably isn’t one. There are always a minority of people with sexual appetites that do not promote survival of the species.

1% of americans are asexual, they have never found anyone attractive. Lucky assholes :slight_smile:

http://www.cnn.com/2004/TECH/science/10/14/asexual.study/

Bogaert’s analysis looked at responses to another study in Britain, published in 1994. That study was based on interviews of 18,000 people about their sexual practices.

It offered respondent a list of options. One read: “I have never felt sexually attracted to anyone at all.” One percent said they agreed with the statement.

I’m sure there are other sexual appetites that don’t support survival of the species but asexuality and homosexuality are at least two. There are also men who prefer extremely fat women (extremely fat women don’t get pregnant nearly as easily as thin women with 0.7 waist/hip ratios), men who prefer older women who aren’t fertile anymore, people who don’t like vaginal/penis sex, etc.

53

FTR, I don’t think the fact that homosexuals exist is anything spectacular. They are in the minority, which is expected. If 90% of humans prefered sex with someone of the same gender (or likes unfertile women, or was asexual) then that would be a problem and we wouldn’t be here to debate it. But 1-2% of the population isn’t going to change anything. Besides, genetics probably only covers 50% of the propensity for something like asexuality or homosexuality. And alot of people have just pretended to have more socially acceptable sexual appetites throughout human history out of shame and fear.

54

Perhaps a bit lower than that, I think, based on more recent surveys that are evidently accepted by gay rights organizations.

From here (which seems to be borne out by several other sites):

There are no doubt a significant number of people who, as you say, are homosexual in orientation but do not identify as such. However, I think the actual rate of exclusive male homosexuality is more likely in the range 2-3% rather than 5%. Of course, a significantly larger percentage of people have had one or more isolated homosexual experiences.

55

I haven’t read the whole thread yet but thought my response might be better if not colored by reading the whole thing before responding since you are inquiring as to my state of mind when asking the question.

1: I am aware that many insects never reproduce but I must admit that I haven’t given their sex lives a lot of thought, especially as opposed to say… my own sex life. If I haven’t couched this question in terms of birds or bees it is because I devote very little thought to them. This question is somewhat akin to asking someone who has just ordered a pizza why they didn’t order a shoe instead. I guess one could eat a shoe but it simply isn’t likely to cross one’s mind and would be of little interest if it did. So yes, insect mating habits are puzzling to me as well… but then again I am easily puzzled. Even your question puzzles me.

2: I think I referenced in my post that many homosexuals reproduce but how much of that is from desire to have children and how much of it is from the pressure of societal norms to conform is open to question. This is especially so when thinking of our very distant ancestors for whom children were probably a by-product of the natural drive to have sex rather than any lofty ideal of having little copies of ouselves pitter-pattering into posterity.

This is one of the best places around for being able to ask a provocative question without having one’s motives questioned but still I feel compelled to say that I am in no way personally against homosexuality (and I HATE that anyone even has to say that). I am also aware that the issue of genes and how they express themselves isn’t always straightforward and is complicated yet further by many genes being in conflict.

I think that with homosexuality as common as it is and as likely to be bred out as it would seem to be at first glance that there is probably something fairly interesting going on there. Not being an evolutionary biologist, I thought it would be quite possible that my question would be the equivalent of a teenager asking the Federal Reserve Board why they don’t just print enough money so that everyone could be rich. I prefer to look foolish rather than to remain ignorant.

56

It’s certainly not a foolish question, and it’s something that has been considered by a number of evolutionary biologists such as E. O. Wilson. I thought that for a non-biologist your question was well-posed and ratherh well-thought out. You hit on a couple of the basic hypotheses that have been invoked to explain it.

I hope that some of the information in this thread will help refine your understanding of some of the dimensions of the problem.

57

With respect to my post just before yours, it may be worth looking at the prevalence of homosexuality in the population compared of other forms of sterility, both physiological and behavioral.

With respect to physiological sterilty, this reference i indicates that, for couples under 35, only about 2% are unable to conceive after 36 months. While some may conceive eventually, a lower conception rate indicates at least subfertility, if not outright sterility. I think we can take 2% as a ballpark estimate of the prevalence of sterility/subfertility in the general population. Offhand, I am not sure what percentage of failure to conceive is due to the male partner, and how much to the female (or how much to both). However, since failure to conceive can be due to either partner, we can use this rate to make a very rough estimate that 1% of males and 1% of females are physiologically sterile.

Physiological sterility certainly must be maintained in the population despite 100% direct selection against it. Physiological sterility is probably to a great extent due to problems during development, or to health issues. It is, however, possible that some of it is due to recessive alleles that are maintained in the population due to positive selection on some other trait they influence; or because of the effect of other alleles in combination that otherwise have positive effects.

Beyond sterility, there are other physical or mental problems that may prevent people from marrying and having children, even those that are perfectly fertile. These include physical and mental handicaps, mental illness, and other health problems.

What is the rate for other forms of behavioral sterility besides homosexuality? It has already been mentioned in this thread that the rate of asexuality - no interest in sex at all - may be about 1%.

According to data available here and here, back in the 1970s, when there was very strong societal pressure to get married and have chlidren, 5% of males and 6% of females aged 40-44 had never married, and a full 10% of females at that age had never had children. Currently, 17% of males and 12% of females aged 40-44 have never been married, and an extraordinary 19% of females have never had children. (It is of course more difficult to determine the number of males who have never had children than that for females.)

So we see that the rate of homosexuality (2-3%) is in roughly the same ballpark as physiological sterility (1-2%) and asexuality (1%). Marriage and childlessness rates imply that even in the 1970s other forms of sterility, whether physiological or behavioral, were much more signficant than homosexuality. Today other forms of behavioral sterility, for the most part voluntary, are far more important.

The gist of this is that homosexuality is no more difficult to explain in evolutionary terms than other forms of sterility, whether physiological or behavioral.

58

I’m sure you didn’t mean to imply that homosexuality is a form of sterility, btw.

59

I believe given the way Colibri was using the terms that exclusive homosexuality would be a form of behavioural sterility.

60

I didn’t imply it, I stated it explicitly. Exclusive homosexuality, that is no attraction whatsover to the opposite sex, may be considered a form of behavioral sterility, even if the person is 100% fertile physiologically. I am trying to distinguish here between physiological sterility, that produced by an inability to conceive, and behavioral sterility, that is, behaviors that preclude mating. In birds, a similar effect might be produced by a failure to develop the proper song or other courtship behavior. The result on evolutionary fitness is the same (to the extent there is genetic control of the trail), whether physiological or behavioral.

(In terms of barriers to hybridization, biologists speak of pre-zygotic barriers (pre-mating and pre-fertilization) and post-zygotic (post-fertilization). My distinction is analogous.)