The effeminate sheep and other problems with Darwinian sexual selection.

[Raster]

http://seedmagazine.com/content/article/the_gay_animal_kingdom

Joan Roughgarden thinks Charles Darwin made a terrible mistake. Not about natural selection—she’s no bible-toting creationist—but about his other great theory of evolution: sexual selection. According to Roughgarden, sexual selection can’t explain the homosexuality that’s been documented in over 450 different vertebrate species. This means that same-sex sexuality—long disparaged as a quirk of human culture—is a normal, and probably necessary, fact of life. By neglecting all those gay animals, she says, Darwin misunderstood the basic nature of heterosexuality.

Male big horn sheep live in what are often called “homosexual societies.” They bond through genital licking and anal intercourse, which often ends in ejaculation. If a male sheep chooses to not have gay sex, it becomes a social outcast. Ironically, scientists call such straight-laced males “effeminate.”

Giraffes have all-male orgies. So do bottlenose dolphins, killer whales, gray whales, and West Indian manatees. Japanese macaques, on the other hand, are ardent lesbians; the females enthusiastically mount each other. Bonobos, one of our closest primate relatives, are similar, except that their lesbian sexual encounters occur every two hours. Male bonobos engage in “penis fencing,” which leads, surprisingly enough, to ejaculation. They also give each other genital massages.

As this list of activities suggests, having homosexual sex is the biological equivalent of apple pie: Everybody likes it. At last count, over 450 different vertebrate species could be beheaded in Saudi Arabia. You name it, there’s a vertebrate out there that does it. Nevertheless, most biologists continue to regard homosexuality as a sexual outlier. According to evolutionary theory, being gay is little more than a maladaptive behavior.

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[saltpoint]

1. It might be best if we just banned science altogether. We don't want to

run the risk that high schoolers would actually choose one or other of the sciences to pursue as a career.

[TheWraith]

8. What was the point of that comment?

This article isn't about disparaging science, it's about getting science right.

[saltpoint]

9. Got it.

[Sal Minella]

2. Yet another example

of how pathetically far behind we are in understanding the things we know.

[imdjh]

3. Or of how irrelevant most of it is.

[ThomCat]

13. Understanding sexuality and how it works in nature is hardly irrelevant.

Given how much effort Everyone spend fighting over sexuality, buying and selling it, legislating it, restricting it, trying to define what is right or normal or natural, and trying to force one view or another upon others, then truly understanding sexuality and how it all works is definitely important.

I really don't see how anyone could really think that the science of sexuality is somehow irrelevant.

[d_r]

4. I'm not expert on this

But there is an evolutionary/biological explanation for homosexuality; I don't know why this is saying that there isn't one.

I don't know the exact statistics, but human males who are second born males are slightly more likely to be homosexual, third born males are slightly more likely still to be homosexual, and so on. These statistical percentages remain whether the boys were raised by their biological parents are not (so, for example, a third-born boy who is adopted and raised in a family where he is the oldest boy has the statistical likelihood of being gay as third-born boys). The hypothesis is that there is some sort of hormonal change in the woman's body after male pregnancies that increases the likelihood of subsequent males being gay.

The evolutionary explanation is much like the explanation for bees. Worker bees will lay down their lives to sting you to protect the hive, and the offspring of the queen even though they aren't able to mate and produce their own offspring. Why? Because the larvas of the bees are their cousins. So helping their survival helps the survival of genes similar to those of the worker bees.

In our evolutionary history, the theory goes that men maximize their potential to pass on their genes by their seed widely and having as many children as possible. Women, on the other hand, are argued to benefit from having few children from few partners and investing in them heavily to ensure their survival to adulthood when they can mate and pass on the genes. This is the explanation for cultural practices like younger girls marrying older men - the more established male in the tribe has more resources to invest in the offspring and ensure their survival.

So if men benefit from spreading the seed widely, if there are limited resources then male siblings would be competing with each other for women. So a man might be gay and not compete for women, but still provide for the extended family by bringing home game and food and protecting from other tribes, etc. He is helping to pass along the genes of his cousins and nieces and nephews, and therefore genes that are closely related to him.

I'm not saying that I agree with this view or promote it, or even that I have it exactly right, I'm saying that there is clearly an evolutionary explanation for biological basis of homosexuality in humans (and other species).

[Ian David]

6. My theory is that the Extreme Religiosity and Gay Genes are co-adaptive.

Being a Religious Fundamentalist increases your chances of suppressing your homosexuality enough for you to pass along your gay genes.

So, every time a fundie rails against gay marriage, you can tell them that all they're really doing is increasing the number of gay children who will be born.

[donco6]

7. I've often wondered if this wasn't the case.

3rd son here.

Why isn't it possible that homosexuality is a natural protective mechanism that springs into action whenever population numbers begin to creep out of control? Viewed this way, my existence is not a maladaptive behavior, but rather a necessary and valued one. But that goes against so many Christian biblical principles it can never be accepted without some huge sea-change in philosophy.

Right now, we seem to be at a pivotal point in our view of homosexuality in this country. We can accept the fact that it is a normal occurence in humankind, or we can cling to outmoded teachings that originated thousands of years ago when nations were desperate for ever more children to throw into bloody battles. It's a toss-up as to how it's going to turn out.

[Scuadrado]

18. A lot of people wonder that.

But it's pretty unlikely.

If there were a gene variant that caused homosexuality when the population grew large, then as the population grew, the people with this gene variant would just be outbred by the people without this gene variant. It'd be pretty strong selection pressure against it.

The typical response to this is to invoke group selection as a possible mechanism. Whether group selection has any large effects at all is pretty controversial, and it would have to have a pretty big effect to account for this.

Dubious as it is, this hypothesis has one good thing going for it. It makes predictions that can possibly be tested. Homosexuality should occur more often in crowded conditions. With humans there are obviously other confounding factors (how many people in more liberal, urban areas with denser populations feel comfortable coming out?). Maybe someone could get some data on sheep (I can't think of another species off the top of my head with a high rate of exclusive homosexuality, as opposed to bisexuality)? It would be quite expensive to set up an experiment just for this, but if there's be some way to survey sheep populations living in different conditions, it would at least provide a test for this hypothesis.


I think a much better hypothesis is that whatever genetic variants make a certain percentage of us end up gay confer some advantage to people with another mix on them. I.e. a heterozygote advantage. The canonical example of this is the ?-hemoglobin allele that causes sickle-cell anemia in homozygous carriers, but confers resistance to malaria in both heterozygous and homozygous carriers. Deadly as it is to people with two copies, it confers a substantial benefit to those with one (in areas that have lots of malaria at any rate). Outside these areas, it's almost purely disadvantageous.

As it happens, there is a bit of evidence that the female relatives of gay males are likely to have more offspring in general:
http://www.springerlink.com/content/q4579x2370758366/

I don't know if anyone has tried to reproduce it.


Another hypothesis is that it's caused by some sort of pathogen (e.g. a virus) that acts on a critical region of the brain at a critical time. In this case, you wouldn't necessarily need to explain how evolution sustains it...except that we know empirically that there's a substantial genetic component (from the Bailey & Pillard twin studies, for example), so unless such a pathogen were relatively new, we'd still have to explain why there wasn't selection against people that had genes that make them susceptible to the pathogen.

Yeah, I know I've rambled on forever.

[TheWraith]

10. That sounds like the flip side to a slightly different theory I read once.

The short version is that rather than it being about reducing competition for reproduction by removing certain people from the reproductive hunt, it's about maximizing the available population. In social animals, any situation where there's group or pack survival instead of just individual survival, there's an evolutionary benefit to a gene pool that periodically produces pure homosexual behavior.

Suppose you have an extended family of 20 cavemen, out of which two are gay. Those two aren't going to be producing children, but they will still be contributing to the overall group's chance of survival, therefore increasing the odds of their genome's survival. Thus, rather than a biological response to overpopulation, it's likely that there's an over all selection pressure benefit to be derived from genes providing a latent chance of homosexuality.

[Xithras]

11. Interesting, but there is a far simpler evolutionary explanation for homosexuality.

I heard this explained in a lecture many years ago, and it makes perfect sense: In species with a high rate of predation or infant mortality, possessing overly specialized mating requirements is actually counterproductive to the survival of the species. As the rate of population loss per reproductive cycle increases, the need to increase the rate of procreation must also increase or the species will simply cease to exist. This actually generates an evolutionary pressure on the species to eliminate preferences in mate selection over time, in those limited species, in order to increase the rate of births. In plain english, the drive becomes "screw anything that moves in the hopes that it will generate an offspring". The problem with this development is that evolution has also instilled within sexual animals a knowledge of the basic steps required for procreation. Insert penis into wet spot, rub till it feels good, make baby. Let things be inserted into wet spot, be rubbed until pleasurable, make baby. When the biological imperative to mate with a partner collides with a lack of a firm evolutionary push towards mate gender selection, homosexual behavior in those species becomes the natural result.

Human babies are born small, weak, defensless, and with crappy immune systems. Their births frequently killed their mothers before the advent of modern medicine. According to some estimates, the infant mortality rate for prehistoric humans may have been 60%-70% regularly, and may have exceeded 90% in periods of high disease or famine. We survived as a species because our ancestors had a LOT of sex, with a LOT of partners, and made a LOT of babies. Individuals who were overly discriminatory in their mate selection had few babies. Individuals willing to screw anyone had a lot of babies. The evolutionary pressure, therefore, was toward the elimination of preferences in sexual partners.

I've believed for many years that the natural sexual state of the human animal is bisexuality. Both homosexuality and heterosexuality represent deviations of this norm, created either by social pressures or genetic variations.

[xchrom]

12. functional bisexuality isn't bisexuality.

it means the pipes work with stimulation -- no matter who is doing the stimulation..

i don't think darwin would have a problem with the end result of stimulation -- meaning i doubt the author's conclusion.

he didn't observe it -- or chose not to make a theory -- of what he observed.
we won't know.

[imdjh]

15. Sounds like mutts with Phd's trying to excuse their random ancestry or their own sluttiness.

[Xithras]

17. Evolution likes sluttiness

The evolutionary endgame is quite simple: He/She with the most babies wins, and the DNA of everyone else gets sucked into an evolutionary black hole. The only real point of Darwinian selection is to find the combination of traits that leads to the highest birthrate and long term survivability of the species.

Morality and ethics play no part, only reproductively beneficial traits matter. If functional bisexuality and "sluttiness" improve the odds for a species survival, then natural selection will favor those traits.

[Ian David]

5. Related thread: IL Teacher Suspended For Assigning Article On Homosexuality In Animals

IL Teacher Suspended For Assigning Article On Homosexuality In Animals
http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=221&topic_id=149047&mesg_id=149047

[LeftHander]

14. In Creation Science there are no genitals....that is icky...nt

[sui generis]

16. at the end of the day, sex is a mechanical activity

it's humans who attach all the drama to specific configurations of pink parts.