Homosexuality and evolution

I made the mistake of reading some of the comments on those last youtube videos. There were some good ones, but they were also laced with the usual grunting assholes complaining about gays and "trannies" and quoting the Bible and making racist remarks about Africans. Let us pass over those contemptible arguments; there's no dealing with them rationally. Spit and move on.

But there's another flavor of argument that annoys me to no end: people who cite science and evolution to support their ignorant misconceptions about human nature. I want to address two, one anti-gay and the other pro-gay, both wrong.

First, there is the reductionist who knows a tiny bit about selection.

interesting point of view, but no. Evolution is all about competition. If you dont produce offspring, you take yourself out of the running. They may help the larger group, but that is more along the lines of the group exploiting a weakness. Their genes do not pass on. In the evolutionary crucible, thats a game over. It doesn't matter what disease you cure, what philosophy you teach, biologically, you lose. Now, again, in modern society, things are more complex. There are more qualities to a life than how many mini-me's you can make, but for the purposes of biology, it ends there.

If evolution is all about competition, how come reproduction in sexual species requires cooperation between two individuals to occur? Have you ever noticed that reproduction isn't actually literally replication? You take your complement of 20,000 pairs of genes, and you throw half of them away, splice the remainder into different combinations, and then you merge those with the similarly mangled set of genes from another person, and you produce a unique individual. Not a clone of either of you -- someone completely different.

That should tell you right away that you aren't the focal point of evolution. You are a test platform for a battery of genes, genes that are shared with other members of your community. Evolution sees the propagation of a pool of genes that tends to produce successful individuals; look up inclusive fitness sometime. You share genes and combinations of genes with your siblings, your cousins, and more distant relatives -- there's more than one way for your population to propagate itself than for every individual to maximize the number of offspring they produce.

I also have to laugh every time some oblivious multicellular animal announces that evolution is all about competition, and that all that matters is how many progeny you produce. Do you realize that your existence is entirely a product of cooperation? Your parents were made up of trillions of cells, almost all of them dedicated to specialized, non-reproductive functions, all in support of a tiny minority of cells that can produce gametes. And of all those gametes, only two combined to make you -- the great lumbering mass of agglomerated metazoan cells that were your parents then dedicated themselves to cooperatively nurturing the little zygote that was you (and which was not genetically identical to either) into a roughly similar lumbering mass.

Further, if that's too abstract for you, consider this: you'd most likely be dead right now if scientists hadn't collaborated to make vaccines against childhood diseases, if doctors and family hadn't worked to keep you healthy and educated. Imagine all those carpenters who built your house and plumbers who put in the pipes and electricians who wired it up; imagine the vast combines that work to deliver fuel for heating and food for eating. Everything that you think is important about you was created by cooperation.

If you think otherwise, go masturbate into a mud puddle and hope that some of your offspring can make it without any assistance.

Here's the pro-gay argument based on evolution. It's just as annoying.

from a view strictly based in the ideas of natural evolution, i always assumed "homosexuality" was as old as the species... and that it was evolution's way of both keeping the growth of the species in check (since humans are one of the few species that have sex for pleasure) and ensuring orphaned younglings have a chance at receiving care, guidence, and protection in their formative years. mind you this is just a personal theory based on the nature of nature...

Do not anthropomorphize evolution. Evolution is not an entity that plans and manages populations, it is not a nanny that cares about youngsters -- if they are orphaned, one evolutionary outcome is for them to die, another is for survivors to support them, and all that matters is whether the population persists. In particular, evolution isn't concerned with keeping populations in check -- it's simply a ratchet that permits populations to strive, and eventually and inevitably they hit physical and biological limitations, or pressure from some other growing population, and then physics happens.

Nothing personal. Evolution doesn't play favorites. It can't: it's just the outcome of chance and physical laws interacting in particular environments.

Here's my perspective on evolution and homosexuality.

Humans are complex organisms whose development is plastic and strongly dependent on environmental influences. There is selection pressure for the population reproduce, which we social beings accomplish with a significant subset of individuals providing sufficient progeny to replenish the population each generation, and with a similarly significant subset of the population working cooperatively to provide a supportive environment.

Evolution doesn't care. All that matters is that the population thrives into the next generation, and that requires that individuals cooperate. Evolution is not a micromanager, either; we acquire random variations purely by chance, some work, some don't, and in general, there are so many competing factors driving our survival that selection cannot possibly fine-tune emergent properties of behavior to such a degree that biology can specify exactly who you will bump genitals with. We are dealing with general tendencies expressed to varying degrees in individuals within a population.

If there is one biological imperative for humans, it is this: love one another. Build communities. Cooperate. Help each other in adversity. Successful populations will express these behaviors to a greater degree.

There are also biases towards favoring sexual interactions with members of a different sex, but that's a secondary priority. Even if sexual preference were non-existent and totally random, women would pair up with men half the time, which would be more than sufficient to propagate our species, especially if the other half are working cooperatively to build safe homes and stable food supplies and provide loving educational environments.

From my biological perspective, the negative behavior that affects the survival of the species isn't homosexuality, but anything that disrupts the cooperative bonds of community and foments hate -- homophobia in humans is the destructive behavior that selection should work against. But keep in mind that if God has lousy aim, evolution is even worse…so we should also encourage behaviors that discourage attitudes that work against our survival.


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My personal view is that homosexuality has as much to do with evolution as, oh, say, bowling. Which is to say almost exactly zero. I agree that love makes for a very effective biological imperative for humans, and I agree that even a 50% heterosexual frequency would be sufficient to propagate the species.

By Jay Clemons (not verified) on 31 Aug 2014 #permalink

Some believe homosexuality is a third sex that is evolving. If that be the case they would be a non-beneficial mutation that cannot reproduce. If that be the case, letting them adopt would be contrary to survival of the fittest and the mechanisms of evolution. I would imagine determining if they are a non-beneficial mutation would be helpful in determining how they should be viewed by the scientific community, and society in general.

By Arv Edgeworth (not verified) on 31 Aug 2014 #permalink

Thinking in terms of selection effects, it seems probable to me that some genes (or gene combinations) may have effects that increase evolutionary fitness in one sex, while decreasing in in the other sex. Say there was a gene which makes one like males, expressed in the female it likely increasing reproductive fitness, expressed in the male it decreases reproductive fitness. Whether it would tend to increase or decrease in the population over time would depend upon the balance of positive and negative feedbacks.

Then of course sexual reproduction is not really symmetric with respect to the sexes. Mitochondrial RNA comes from the female. Y chromosomes are passed from father to son without mixing, i.e. except for mutations they are simply copies.

I'm not nearly as optimistic about evolution favoring cooperation, either in humans or other animals. Think of male lions increasing their reproductive fitness by killing cubs when they take over a pride. Or males in rut. Again sexual asymmetry seems to favor aggressiveness in males more than in humans (is this still true for spiders???). In any case as long as aggressiveness produces a reproductive advantage, evolution may favor it over cooperation.

By Omega Centauri (not verified) on 31 Aug 2014 #permalink

... Yes I have a science background.

Here's an hypothesis.(An/A?)

That social groups that share a gene pool benefit from adults that do not reproduce but are available to the community in other ways. Lesbian and gay people are one example of these individuals. Lesbians, for example, can fulfill a need for older knowledgable, experienced women who survive longer, and whose knowledge survives longer, because they are not at risk in childbirth.

We still see LGBT people “pioneering”, that is developing and exploring in areas that are too risky for child rearing groups to undertake. (Even when it’s as risky as moving into run-down areas and refurbishing houses.)

Gene pools that produce LGBT people have wider resources, are better able to explore and take advantage of situations, to some extent have better defenses and in general can compete and win over pools that lack these individuals.

A very interesting article on a topic I've always found fascinating (why does homosexuality actually exist) I do understand that homosexuality isn't something bad for a species as long as there are enough members of it who actually have descendance. But, why does it actually exist? Normally evolution of any species follows a path that is the result of the best adapted to the environment surviving. So, in the case of homosexuality in living beings... why would it even exist? From a biological point of view, it doesn't have any advantage over being heterosexual, and more so in species that don't cooperate with each other. So, why does homosexuality exist? Just per chance? Does it have any actual benefit for the individual?

All this I ask from a biological point of view. It's very clear for me that there is no problem in anybody being homosexual :)

I must have missed the bit where somebody demonstrated a genetic basis for any of the paraphilia...

By Craig Thomas (not verified) on 01 Sep 2014 #permalink

To "Richard Dawkins":
My Lorde never permits that His creatures be terrorized, even less, being eaten by someone else. This world containing predators and preys is a monstrous design. If your god did it, he is the most stupid designer I have seen.

My lorde, the Almighty Pink Unicorn, only creates things for love, and He loves you too, He promised that will give to you pink popcorn eternally, in the havens. The world is pink, the Universe is pink, think pink. The design of yours god is so bad that he has designed you in the havens eating one celled pond because He was drunk and made another mistake, thinking that you have the same preferences as amoebas...

Cam'on, stop wasting our time mixing science with religion...

By Louis Morelli (not verified) on 02 Sep 2014 #permalink

To "Richard Dawkins"
Why the tiger roar begore attacking the prey? Maybe he likes hunting a prey running, the meal becomes hot? My hipothesis is that tigers mimicks what it see in the sky: every time that came a storm, the sky roared. So, he knows that the storm will fall over the prey, and a thru storm needs some roaring. This is an evolutionary prejudice or a benefit to tigers? Neither one, it does not matter, tigers were born for roaring. same thing for yours "amoeba proteus". It was born with that smell, it had haven food with that smell and the smell is a factor for not eating its equals, so, the smell helps it to survivor, evolution does not care about. Why fox keeps that bad smell? We don't know because we don't know what the fox says... And I can't understand why yours god created predators, evils, also because nobody knows what yours god says...

By Louis Morelli (not verified) on 02 Sep 2014 #permalink

If you dont produce offspring, you take yourself out of the running.

Which totally explains why the world has trillions of ants in it, right?


By Calli Arcale (not verified) on 02 Sep 2014 #permalink

I'm often amazed at how little, in this "enlightened age", human beings have the capacity to understand. Evolution and homosexuality, apparently, can be both biological and mythical depending on your belief system. The human emotion of "love" has nothing to do with evolution or homosexuality. In fact, human males, like all primates are genetically engineered to reproduce with as many females as he can. It is a biological urge that many males cannot resist while some can once entered into a symbolic monogamous relationship with a female and remain monogamous. The reason homosexuality is know so well in the human species is because our brains have allowed us to become the only large species on the planet which can consciously manipulate our surroundings to the point that we can survive and multiply without abandon. Unlike most large species virtually any human, no matter what their genetic flaws, lack of survivabilty , lack of inteligence, basic unattractiveness to the opposite sex (from a reproductive viewpoint) can find a mate, survive and achieve a positive fitness ratio. Its true, we have "evolved" to the point where we take care of those less attractive from an evolutionairy standpoint as a group. We have started to reproduce and survive without abandon. Homosexuality is a genetic trait of some sort. We are too politically correct to look for that trait. If it is found would we try to eliminate that genetic "flaw" if you are a prospective parent? We reproduce with no care for the future. Like any genetic trait in a population that has gone unchecked it will be expressed. Its not a choice, God didn't put homosexuals here to test our faith. Homosexuals in my experience, are better people than most heterosexuals, statistically speaking. I wish they could (would) reproduce, the world would be a better place. The fact that there are more now than there were long ago is because there are more people and more people survive. Simple as that.

Great article Dr. Myers - thank you.

I find it funny when some anti-homosexual people demand that people who are strongly homosexual act heterosexual. I mean, marrying their daughters and passing on their genes?

Maybe for a different reason than us, they don't believe in a homosexual gene. (It's the devil at work). And they fight gay marriage while doing so, as though promiscuous homosexuals marrying their daughters is better.

Nothing rational about their positions.

So many of our inherited characteristics are complex that don't interfere much with species survival.

By Howard Brazee (not verified) on 03 Sep 2014 #permalink

@7, about genetic basis. I'd be fine if there were no basis in DNA (epigenetics, fetal environment, and other non-genetic stuff being messy enough) but there's been some evidence about Xq28 and a piece on chromosome 8. I'm not an expert in the homosexual gene papers, but folks interested in MAGE genes notice Xq28 papers, and if you look both ways you may even remember the papers. Here's a start: http://en.wikipedia.org/wiki/Xq28. PMID:15645181 is maybe worth a look if you want to exert neurons, but see 20057505 about 7q32 not looking so great in other data. Bailey still hasn't published a paper on the latest data I think, which is said to like Xq28.
For main post, the first example error I had compassion for - they may not be so dumb, just need more education. Always remember that it's DNA replicating, not us. But the second one made me guffaw. Not quite as much as comment #2 though.

It evolved as a defence against cannibals.
If you want to catch men to eat, just tie a woman to a tree and when a man comes along to try to reproduce with the woman tied to the tree, club him over the back of the head and eat him.
Homosexual men simply don't fall for that trick therefore ensure the continued survival of the consumee group.
Ok this doesn't explain gay dogs and geese but perhaps there is something there? Male animals may be slightly prone when distracted by females. Could gay animals be getting into fewer fights?

PZ, I get the impression that you are attributing purpose to evolution:

"Evolution doesn't care. All that matters is that the population thrives into the next generation, and that requires that individuals cooperate."

The mechanism that produces adaptations is natural selection, which is a simple, mechanical process. Genes that are good at getting themselves copied become more common in the population, and genes that are less good at getting copied become rarer, or even die out. There is nothing in the mechanism that "cares" about a gene's effect on the population as a whole. This explains, for example, why some animals eat the young of their own species. Richard Dawkins has explained this at length in multiple books, as I'm sure you're aware.

"Evolution is not a micromanager, either; we acquire random variations purely by chance, some work, some don’t, and in general, there are so many competing factors driving our survival that selection cannot possibly fine-tune emergent properties of behavior to such a degree that biology can specify exactly who you will bump genitals with."

Reproduction is the ultimate purpose for which natural selection "designs" organisms. The choice of which sex you mate with is not a minor, unimportant detail - exclusively mating with your own sex will reduce your reproductive success to nothing. (Apart from the possibility of propagating one's genes indirectly by helping relatives to reproduce.) Even animals with simple nervous systems apparently don't have much difficulty knowing which sex to mate with, so it's not a difficult problem for natural selection to "solve". It has achieved far more impressive feats of "micromanagement", such as giving human beings the ability to communicate complex, abstract ideas through speech.

Human sexuality is definitely the result of a complex interaction between genetics and environment. (It's hard to see how the wide variety of fetishes and paraphelias, or even the humble blow job, could be explained in terms of reproductive advantage.) That doesn't change the fact that a fairly common sexual preference that greatly reduces reproductive success is deeply mysterious. There must be an explanation, but I for one have no idea what it is.