This is the kicker. Unless you postulate a world-wide, totalitarian government, it would be impossible to change the “overall human genetic composition” since there are so many of us. It would be easier (but not easy) to do it on a smaller scale, but then you’d have to have a government and scientific collaboration over may generations to pull it it off. Theoretically possible, but so many practical problems that it’s hard to imagine a successful venture.
If you run a breeding program on human beings, your most likely result is a human being with increased capacity for getting around breeding programs.
You can breed dogs and horses, but humans are just as smart as you, and fornication is a very strong motivator.
Although it does bring to mind Robert Heinlein stories. There was a fundation that searched records to identify people whose grandparents all lived to 100. They provided social events to bring together these people, and financial benefits if they married.
Their rationale was that living to a hundred was proof of good genes.
I might have started at a slightly lower number, but the idea was interesting.
I’ve always wondered about this. Dogs seem remarkably plastic. A few dozen generations, and you can get to Great Danes…or Chihuahuas. But cats, from tigers to tiny tabbies, still always look like cats. Is there some “meta-genetics” going on, that makes dogs more susceptible to change?
The same thing might work to promote interracial parenting, on the principle of “hybrid vigor.” (I don’t know if that idea has any currency at all, but when I was a tot, it was largely believed that mixed-race people, like mixed-breed dogs, were the healthiest. At very least, it reduces the chances of doubled recessives.)
A lot of good and thoughtful answers. I’m here to put in a simplified one.
Yes, it is not only practically/scientifically viable, people have been doing it for thousands of years. Mating has always had an element of it built in. Most humans are more attracted to health than to disease. To power over weakness.
If you define it such that you are ONLY considering completely externally controlled, government guided mating, then “viability” depends on how correct the science actually is, AND on how …wise the people are who decide what is to be controlled for and away.
I read a proposal in a science magazine many years ago, to the effect that we could solve the energy crisis, world hunger, and the problem of living space all at the same time (for the moment at least), by breeding everyone into being only two feet tall.
Bottom line, success in any venture isn’t entirely objective.
I question your premise somewhat. The weight ratio Great Dane / Chihuahua is similar to the weight ratio Tiger / Domestic Cat. And what’s the metric for claiming that appearance or behavior is more variable among dogs? It may be true, but it’s not obvious to me - my impression is that dogs of all sizes seem rather similar, just as much as cats of all sizes seem similar.
Technically, phenotypic “plasticity” is response to environment for a given genotype, so that’s not what we’re interested in. The basic measure for responsiveness to selective breeding is the genetic diversity of the population. Other things being equal, the more genetic polymorphism that’s available, the further you can “push” a heritable trait to an extreme by selective breeding. Once this “standing” genetic variation runs out, things grind to a halt. You end up with an inbred population, all with identical genotype at the loci relevant to the trait. Any further change requires fortuitous new mutations that would take orders of magnitude more time to arise.
Human nucleotide diversity is known to be low compared to other species, see here:
http://www.nature.com/ng/journal/v36/n11s/full/ng1435.html
I don’t know if there are any comparable data on nucleotide diversity in dogs or cats, I can’t find any.
The kind of society required to pull it off would be an unintended consequence of it’s own. At least to those who did not fit in.
That is if one started out on this project with benevolent intentions to begin with.
Can it work? Yes in theory.
You can call it “Eugenics” but it’s going to be much more, and much worse.
To pull it off world wide would require a powerful, one world, fascist type government or equivalent.
People will become cattle, even the members of the so called master race will be little more than glorified cattle. Pet cattle.
Lovely world where you are told IF you can breed, and with whom and when, that is if you were determined perfect enough at birth to live period.
And considering that the human race actually suffers from very low genetic diversity, i imagine the luxury of breeding to be handed out only on an as needed for maintenance / replacement level once you have the species where you want it, and you will not in any way shape or form have any choice in your breeding partner.
And some sort of euthanasia program will be needed to deal with the defectives.
And since it will be impossible to 100% guarantee no defects ever arise, cause genes are just silly like that sometimes, even 2 absolutely perfectly genetically matched breeders may turn out a little bobby or susie that requires termination due to defect.
But that is ok, because the euthanasia program was instituted long ago to deal with the non conformists and other undesirables.
Yes i know, you are thinking we just wrote a new movie of the week for the SciFy channel, but think about it, All of what would need to be, to pull it off.
I’m not all that versed in genetics but it occurs to me that if you start selectively breeding and that selected breed becomes the dominant genome isn’t that selected population of ubers going to be especially susceptible to previously unknown or mutated diseases that may develop over time that can effect them vs a more widely variable population genome ?
Deleting deleterious alleles will, in many cases (maybe most cases) have bad consequences. Evolution might have kept those alleles in equilibrium against a still worse outcome. As a classical example one can look at the mutation for sickle cell anemia, which confers resistance to malaria. Now, of course after malaria has been eradicated…
We must be humble for a long time, until we know much more than we do now. Of course, there may be trivialities like Huntington, but meddling with genes in humans is not going to create a super race.
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Tiger is not to domestic cat as Great Dane is to Chihuahua. The proper comparison for cats would be to put something like a Maine Coon on the upper end, not a tiger.
Well, you could equally say Wolf vs Chihuahua. A wolf is about the same size as a Great Dane. I don’t think you can cut out large cats just because we don’t choose to have large domestic cats.
I assume that Chronos’s objection is that a tiger is not the same species (or even in the same genus) as a domestic cat. I have two reasonably large domestic cats (Maine Coons who are wonderful pets, but the size and the fur can really get annoying) and they’re nothing like a tiger. Or a bobcat, which is much closer in size to my two guys. The bobcat is Lynx, the tiger is Panthera, the domestic cat is Felis. Maybe you could argue something like the wildcat, but even then there’s crossbreeding.
Anyway, regarding Heinlein, there’s basically two examples. There’s the overarching Howard Families running through a lot of his later work. That was initially incentivizing people who had a long-lived family history to marry and pop out lots of kids. There’s also the one-off of Beyond This Horizon, which proposed being able to specifically examine gametes for alleles (indirectly, by looking at polar bodies and non-desired spermatozoa) and only combine the best via in-vitro fertilization, which would then be implanted into the mother for normal gestation and birth. Of course, Heinlein also got the number of human chromosomes wrong in the novel.
Depends what you are Eu-ing for… Selective breeding emphasizes certain characteristics. Are they linked or correlated to other (perhaps desirable) characteristics. I recall a discussion once on heritage breeds, that mentioned that selective breeding in farm animals tended to make them extremely dumb - since for example, pigs were selectively bred for meat production, so ignoring basic intelligence and survivability in preference for size and speed of growth slowly eliminated “smart” genes from the gene pool - to the point where sows were so stupid they had to be restrained from rolling over onto their litter. Same with so many “bred” animals - racehorses are at the limit of thin and light vs. big muscular and fast, to the point where broken bones at far more common. Many dog breeds are pretty but stupid, high strung and some have hip problems.
Even for humans - sickle cell double gene is deleterious, but a single gene apparently helps against malaria, hence the prevalence in African areas prone to malaria. Eliminate it by whatever means, and you better have a good malaria treatment or mosquito elimination policy going. And so on…
Evolution doesn’t work like this. There are plenty of alleles that are unmistakably bad. The reason they don’t get eliminated is that rare recessive traits hardly ever get expressed. And when that unlucky baby who got two copies of the bad gene dies, all they do is take two copies out of the gene pool that has millions of copies of that gene.
The selective pressure on rare recessive genetic diseases is really really low, because the odds of getting that gene expressed is the square of the frequency of the gene. And that’s why inbreeding is such a problem, because the odds of your mating partner being a carrier for the same rare recessive trait is much higher than chance.
And so the equilibrium is between the selection against the gene, and the frequency of mutations that cause the gene. All coupled with a healthy heaping of random factors and genetic drift.
It would depend on the point of the eugenics. If it was to breed a certain type of biological human then yes. But if the point is to weed out undesirables I would say no. Humans will always find a way to disparage a subset of the population.
Yes. If a scientist who knew nothing of dogs saw some chihuahua running wild in a pack, he’d never in a zillion year, short of DNA testing, think they were Wolves.
Are you serious? Smaller, less hairy, otherwise similar appearance; similar behavior. I think it’s immediately obvious that they are closely related.
https://motherboard-images.vice.com/content-images/contentimage/no-id/1469638203185825.jpg
Although there are other breeds that look a whole lot less like wolves than a Chihuahua.
For two hundred years Dogs were considered a separate species than wolves. Then there’s *Canis latrans *compared to wolves “Smaller, less hairy, otherwise similar appearance; similar behavior.”
The African wild dog (Lycaon pictus) and the dhole (Cuon alpinus) looks similar and are not only a different species but a different genus.
I wasn’t commenting on the speciation question. You claimed that Chihuahuas bear no resemblance whatsoever to wolves.
No, I didnt.
Then I don’t know what point you were making when you said:
Changes in size are generally one of the easiest and quickest traits to evolve - pygmy species are very common. A scientist might very well suspect that a Chihuahua is a pygmy version of a wolf.
If a size change like this happens in nature, the pygmy soon becomes a different species. The reason that Chihuahuas and wolves are still interfertile (setting aside practical considerations) is because the size change was brought about rapidly by artificial selection.
So I don’t think the size difference between the wolf and Chihuahua speaks to the relative “malleability” of the wolf/dog when placed under artificial selection. Compared to what? The best measure of the likely response to selection is the genetic diversity of the species. There may be data on this for dogs, but I can’t find it.