I apologize if this question has been asked in some form or another before; a search on the word “evolution” brings up so many threads it’s like searching the Library of Congress. Anyway here goes (BTW: I’m not an evolution doubter, but I would like to understand the following) :
There’s something that seems like circular reasoning to me. The theory of Evolution by Natural Selection says basicly that traits that are favorable to a species survival will tend to propogate and continue in that species. Fair enough. But then any traits a species happens to have are attributed to natural selection, on the grounds that unless they’re a random selection-neutral feature, they must contribute to the organism’s survival in some way. Especially with something as complex and poorly understood as human behavior, many of the purported reasons for certain features seem more like “Just So” stories. To use a provocative example, if there is a gene for gayness, then gayness must offer enough benefit (possibly to relatives of that person) to be worth lowering the chances of reproducing.
There is a lot of wiggle room in the whole nature vs. nurture area of things. Nobody knows yet what causes homosexuality, if anything actually causes it at all.
Let’s suppose that homosexuality is always caused by a gene (the gay gene, hehehehehe) and that gene was the result of a random mutation back in the day. If he only has sex with men, he won’t reproduce. But, many gay males also have sex with women, for a variety of reasons, so the “gay gene” can be passed on.
Also, a single individual being less likely to reproduce is not much of a threat to the species. If the gay gene were in 98% of people, then it might be, but it’s not, so it isn’t.
Well, the traits got there somehow. Presumably, they were selected for (unless, of course, they are in the process of being selected against) somewhere along the way.
As for “gayness” (or is it “gayosity”?)…well:
It tends to lead to fewer children (though it is hardly strictly true that gays don’t have childred, as my very existence proves), and less demand on resources. A certain portion of the population being born gay could be a good thing. Of course, we don’t know if it’s genetic…
Of course, that last part is just me making stuff up…
First off, let me say that attempting to apply evolution by natural selection to human behavior is risky at best. I’m not even going to approach the homosexuality issue.
Secondly, it’s perfectly possible to have deleterious genes in a population. They’re being produced all the time. And when you do the math, it turns out that they’re extremely difficult to eradicate completely from a population, especially if they’re recessive. Their prevalence will shrink to a very low level, but there will always be people here and there carrying the genes. Albinism, for instance. Extremely rare, definitely deleterious, but still around after all these years.
I am slightly luke warm to the nasty Idea of a gay gene. Can we be more anti-PC. That just seems so silly but it is just an example I understand.
But maybe in todays society, having currency and technology. Homosexually and single adults may be a overflow value that keeps the world moving with or without reproduction, letting there be less stress or concentration on the family allowing reproduction to occur at a more balanced safe rate. Keep this hush hush, Baptist WASP families would hate to find out that a gay mans sexuality is the key to the Universal balance that keeps their children going to DUKE.
I think that there is a tendency to try and find a positive spin to any genetic tendency, when in fact it probably is a negative for the species. The species simply has other benefits that compensate.
Evolutionary psychology (what used to be called sociobiology) is a relatively new field and is considered somewhat controversial for all the reasons already cited. Because human beings can pass on complicated behavior patterns culturally as well as genetically it’s almost impossible to say what has evolved and why. Reasoning backwards from a trait to a reason for that trait is always risky, even for physical structures like a bird’s wing.
Evolution by Natural Selection is no longer applicable to human beings, nor has it been for quite some time. Certainly there are always selection factors at work determining who gets to reproduce and who doesn’t, but those factors are to a large degree no longer natural but societal.
In our society, our medical establishment is dedicated to the proposition that every life is worth saving, no matter how dire the ailment or how crippling the handicap. Obviously, human beings born today without the use of their legs are no longer automatic lion food. Whereas once the “unfit” members of our species were culled by natural processes, like those of any other species, we now have the capacity and desire to protect them.
The selection factors that work upon us now as a species are largely derived from social factors, such as fashion and aesthetics. But even these factors don’t do much to change us as a species, as our society has become so diverse that there is literally “someone for everyone.”
It’s possible that we may soon take control of our own evolution, via the use of gene therapy to remove certain conditions, syndromes, etc. from our unborn children, and thus from the gene pool.
One thing to remember is that the environment (climate, food supply, competing species) is constantly in flux. Therefore, there is no “best trait” for all situations and “fittest” is a moving target. So, new traits evolve through whatever means and they either succeed or they don’t.
Any traits possessed by a species are not necessarily attributable to natural selection. Many factors influence the presence or absence of a particular gene in a population, including:
Natural Selection - If a gene gives a survival advantage to those possessing it, it will tend to become more common.
Genetic Drift - If a particular gene, say one for blue hair, exists in a small population, say only four individuals, it is not too unlikely that, due to chance alone, it would become the only gene in that population in a few generations. The larger the initial population size, the slower the drift, but it will still always be present. Basically, this is just fluctuations in frequency due to random effects.
Mutation - Random genetic mutations constantly introduce new alleles into a population. For instance, if everyone with a sickle cell hemoglobin allele died tomorrow, it wouldn’t be long before this allele reappeared, as it is only a single amino acid different from regular hemoglobin.
Immigration/Emigration - A population may have only a single allele for a particular phenotype, but due to individuals moving into the population from outside, new alleles may encroach.
There are a few more, I believe, but I have left my Evolution notes at home. Please forgive me.
Anything as complex as a behavior probably has many genetic and behavioral components, so let’s avoid discussing a single ‘gay gene’ and use our blue hair gene. It may be present in a population because people with blue hair are hot and get to reproduce all the time. It may be there because it recently randomly mutated into the population. It may then become more common due to genetic drift. It may have been introduced by a blue-haired foreigner who immigrated into the population. Most likely it is a combination of several of these.
To make a long story short, evolution does not proceed merely as a result of natural selection. Natural selection is merely one of the mechanisms of evolution. It was the first noticed, probably the most prominent and best understood, but not the only one.
The equation for the frequency of a gene in a population is similar to the Conservation of Energy equation or the Drake equation. There are a bunch of components that must be summed to find the frequency:
Freq of gene p at time t = initial frequency + adjustment due to natural selection + adj. due to genetic drift + adj. due to immigration/emigration + adj. for mutation/back mutation + adjs. for whatever other effects there might be.
Hope this confusing rant helped somewhat. Invitations are extended to anyone who can remember any other mechanisms of evolution.
OK, I want to squash, once and for all, the notion that genetically controlled homosexuality’s purpose is to control population growth.
Natural selection cannot produce genes that benefit the population. Natural selection must work on genes that benefit the individual the possesses them.
Imagine that there was a gene that caused homosexuality when population levels became too high. Well, when population levels become too high then the people with that gene stop reproducing. The population declines. But everyone who is left over must lack the gay/density gene. Next time the population rises, no one turns gay because the gene has been wiped out.
It is possible to imagine that a gay/density gene might exist, but for reasons of natural selection we would never expect it to actually occur.
When I was in college one of my professors claimed that there was a single known and documented case of a spontaniously (sp) occuring sickle cell mutation. IIRC, the person was white and lived in Indiana and died somtimes is the 1950s. Sorry I don’t have a cite.
“Wouldn’t be long” in an evolutionary sense. I’m not talking a couple of weeks here. But in a few (dozen?) generations with a large population, any mutation is likely to appear (again, I’m talking single point mutations, not growing three heads or something). Also, a person in whom such a mutation occurred would not likely be noticed, as a single sickle cell hemoglobin allele causes no adverse effects. Only in homozygotes does sickle cell occur, I believe. I’m sure someone will correct me if I’m wrong.
I don’t think this is true. The smallest unit that evolution can operate on is a population. Individuals cannot evolve. So altruistic genes can and do arise in populations. Bacteria have genes for suidcide which get expressed when their is a strain on the colony’s resources. A honey bee hive has specialized its reproduction so that 99% of the colony is sterile. The genes that make worker bees sterile give the individual zero chance of reproducing, but it helps the hive as a whole. These genes were selected for by natural selection.
Genes survive by individuals passing on those genes. Its really that simple. A “gay” gene (assuming its recessive) could have an obvious purpose not unlike that of workers in a beehive. If you’re gay then theoretically you won’t reproduce. You can therefore spend all of your time caring for your siblings (which have a high percentage of your genes). It really doesn’t matter if they’re your kids or not, as far as genes are concerned. Care for siblings can translate into more of them surviving and thereby passing your genes on.
As for the beehive, male bees have only one set of chromosomes. Females have two. Queen bees mate only once and save the sperm for their entire life. Any reproduction is done with exactly the same male genes. So any worker (female) can be assured that her sister shares more of her genes than her mother does. Instead of being related to your sister and sharing 1/2 her genes you share more on the order of 3/4 of her genes. Therefore it makes genetic sense to spend more time caring for your sisters than you would worrying about reproducing yourself.
Societal selection IS natural selection. It operates in animals too. Remember, it’s not just about who gets “culled” but who has reproductive superiority. In all social animals, from deer to dogs to apes, the individual with the highest social standing has reproductive superiority over all the others. This is sometimes because of brute strength but can also be due to boldness, cunning or other talents. The same applies to humans. It’s also true that while animals don’t have medical technology, some have been seen to care for the sick and disabled.
It’s true that birth control complicates the dominance/reproduction relationship a bit. But the fallacy here is to think that what animals do is natural, while what humans do consciously is unnatural. Not so. Our ability to heal the sick and control birth are aspects of our innate talents, and their effects are just as “natural” as anything else.
DrDoom, I am not sure I understand your question. What I meant by that quote is that our brains evolved by natural selection, and so the things we can do with our brains, including developing medicine, are in that sense “natural.” I do not claim that genes act directly on illnesses.
First of, I would like to point out that anybody who believe natural selection is not at work within humans was selected for themselves. First, some one sperm beat out a whole boatload of others. Then, your genes allowed you to survive and grow into an embryo, and later a fetus. If you had an unfavorable mutation, you could easily have become a miscarriage–many do. Then, you didn’t (presumably) have genes predisposing you to some horrible crippling illness that kills you at age 5. And if you have kids, then you obviously do not have genes causing you to have completely useless sperm/eggs. So yes, natural selection is alive and well in the human species.
Now, on to population genetics. I am living, breathing proof that if there is a gay gene, it is passed on–at least sometimes. But at the same time it’s hard to argue that it leads to fewer children overall. Now that that’s settled…
…On to the stickier issue: can we select for something that does not directly increase the chances of a given individual passing on their genome. Traditionally, natural selection tells you that no, this doesn’t happen. However, the natural world is positively overflowing with examples of species wherein individuals die, or fail to reproduce, to benefit the population. MOreover, it seems that in many of these cases it is something that all–or most–of the population has in their genome, but is only activated if the situation demands it. So it’s possible that, for example, everybody has the “gay gene”–so it always gets passed on–but it only becomes active in some portion of the population when numbers get too high.
Now, it’s worth remembering that in terms of gay____ (what is the proper ending for that?), we don’t know if there’s any genetic factor, or whatnot. But I’m just running with the OP…
I am almost sure that genetic studies were never done on gay-parents to determine the possible dominance of a tentative gene. Nor have I ever heard of any folklore evidence that homosexuality is inherited, in any manner. It’s possible, of course, that H is a result of a spontaneous mutation, but then the frequency of it would probably exceed all other spontaneous frequencies combined. Neither it appears as a somatic chromosome mutation; sexual chromosome is even less likely.
So, I do not think it is genetic. I do not want to say what I think of the etiologyof H, though. Besides, it is my private opinion.
