Assume total heritability, random mating, additive genetics, and a single 50% truncation event. In the first generation, the right tail becomes 4x larger as a proportion of the population, but it gets smaller in equilibrium. The new mean is 0.8 standard deviations above the old mean. The new standard deviation is 0.6 times the old one. When it reaches equilibrium and becomes a Gaussian with those parameters, the crossover where the old population had a thicker tail than the new is about two standard deviations. At three standard deviations, the new distribution is only 1⁄10 of the old distribution. But I don’t know how much time it takes to get there.
Thank you, I’m pretty surprised by that result. Two questions: does assortive mating merely slow down that process? And is there any way to increase the both the average and the standard deviation?
You need new mutations to increase the standard deviation, that takes a lot of time and a big population size.
Also, having a genetic disorder applies larger selection pressure to the other genes.
If we are to think of some real ‘eugenic’ population bottleneck, such as WW2 related, the correlation between intelligence and survival is, frankly, shit, plus a lot of small, geographically co-located sub-populations where a bunch of beneficial genes have been slowly increasing in prevalence get completely wiped out, with loss of all copies of that gene.
Bottom line is, selective breeding of larger corn kernels works quickly because the nature hasn’t been breeding for larger corn kernels to begin with, it has been breeding optimum kernel sizes, and to get large kernels you’re just selecting genetic disorders. There’s nothing that you can wreck about the brain that would turn you into a genius, there’s a plenty of things you can wreck about growth that would make corn kernels big.
It seems to me that this would work much better for traits that can be accomplished through loss of function (e.g. larger corn kernels, through loss of function of regulator genes) than in general. At too high mutation rate, complex functionality can’t be preserved.
One thing to keep in mind eugenics wise is that pretty much all the breeding methods we employ for other species are dysgenic—we are producing cripples to our own benefit or amusement. Damage this, damage that, select this bad gene, that bad gene, and you get yourself docile floppy eared dog with the IQ equivalent of severe mental retardation, compared to a wolf.
One thing to keep in mind eugenics wise is that pretty much all the breeding methods we employ for other species are dysgenic—we are producing cripples to our own benefit or amusement.
I assume by ‘dysgenic’ you mean ‘less fit than unbred specimens for reproductive fitness in the wild’. (You couldn’t mean ‘reproductive fitness’ in general, given how many dogs there are compared to how many wolves there are now.)
This seems like an odd point to make. Of course we breed animals to be less-reproductively-fit-in-the-wild—if they were already ideal for our multifarous purposes, why would we be explicitly breeding them at all? (If they were already ideal for eating or being pets or whatever, we would simply capture & use them or raise them normally without any interference in their reproduction.)
It’d be a pointless point if there was a symmetry between fitness in the wild and fitness for our purpose. There isn’t—fitness in the wild is very seldom improved by loss-of-function mutations, whereas fitness for our purposes, starting from the species that have been evolving for fitness in the wild, very often is. Rapid success at breeding larger corn kernels is not going to generalize into rapid success at breeding ubermensch.
fitness in the wild is very seldom improved by loss-of-function mutations, whereas fitness for our purposes, starting from the species that have been evolving for fitness in the wild, very often is.
There’s no reason evolution would have already have optimized for all the intelligence-related alleles; if it had, they would have reached fixation.
Rapid success at breeding larger corn kernels is not going to generalize into rapid success at breeding ubermensch.
I think it is. All the genetic data seems to point to: much of intelligence is genetic, highly polygenic, not fixated, and additive. All of that translates to breedability: we have a lot of easily identified variants present in only parts of the population; hence, breedable.
There’s no question that evolution can continue. The issue is that the rate you can attain for different traits differ. For example, evolving smaller animals from larger animals (by a given factor) is an order of magnitude faster process than evolving larger animals from smaller animals. ( http://news.ucsc.edu/2012/01/body-size.html ). I think you wouldn’t disagree that it would be far quicker to breed a 50 point IQ drop than 50 point IQ rise?
we have a lot of easily identified variants present in only parts of the population
I guess you refer to those studies on intelligence genes which flood the popular media, which tend to have small effect sizes and are of exactly the kind that is very prone to superfluous results.
For example, evolving smaller animals from larger animals (by a given factor) is an order of magnitude faster process than evolving larger animals from smaller animals. ( http://news.ucsc.edu/2012/01/body-size.html ). I think you wouldn’t disagree that it would be far quicker to breed a 50 point IQ drop than 50 point IQ rise?
But what does that have to do with breeding for our objective purpose? It may be easier to destroy functionality than create it, but evolution is creating functionality for living in the wild and doing something like hunting mice while we’re interesting in creating functionality to do something like understand human social cues and trading off against things like aggression and hostility towards the unknown. In both cases, functionality is being created and trading off against something else, and there’s no reason to expect the change for one case to be beneficial for the other. Border collies may be geniuses at memorizing words and herding sheep and both of these feats required intense selection, but both skills are worse than useless for surviving in the wild as a wolf...
I guess you refer to those studies on intelligence genes which flood the popular media, which tend to have small effect sizes and are of exactly the kind that is very prone to superfluous results.
The original studies, yes, the ones like candidate-gene studies where n rarely is more than a few hundred, but the ones using proper sample sizes like n>50000 and genome-wide significance level seem trustworthy to me. They seem to be replicating.
Well, my point was that you can’t expect the same rate of advances from some IQ breeding programme that we get when breeding traits arising via loss-of-function mutations.
Sure, there’s a huge genetic component, but almost none of it is “easily identified”.
Generally you can expect that parameters such as e.g. initial receptor density at a specific kind of synapse would be influenced by multiple genes and have an optimum, where either higher or lower value is sub-optimal. So you can easily get one of the shapes from the bottom row in
i.e. little or no correlation between IQ and that parameter (and little or no correlation between IQ and any one of the many genes influencing said parameter).
edit: that is to say, for example if we have an allele which slightly increases number of receptors on a synapse between some neuron type A and some neuron type B, that can either increase or decrease the intelligence depending on whenever the activation of Bs by As would be too low or too high otherwise (as determined by all the other genes). So this allele affects intelligence, sure, but not in a simple easy to detect way.
There isn’t—fitness in the wild is very seldom improved by loss-of-function mutations
I am not sure this is generally true.
The wild equivalent to “fitness for our purposes” is a drastic change in the environment which starts to select for different criteria. In such conditions organisms certainly select for new-useful-function mutations, but they also select for loss-of-no-longer-useful-function mutations. Functionality tends to be expensive (e.g. in energy) and if you don’t need it, you’re better off discarding it.
Those drastic changes rarely happen, though. In humans, the most recent very well known one was adult lactose tolerance—something that switched lactase off in adulthood no longer does.
edit: and somewhat back to the original point with regards to eugenics—humans have been evolving intelligence for a while already, so selection for intelligence doesn’t seem like a dramatic change.
That, by the way, is an interesting example of both adding functionality (now adults can drink milk!) and losing functionality (the gene which turns off lactase production in adulthood got broken and no longer works in many people).
Yeah. Anyhow, my original point has to do with attempts to breed humans for intelligence. Humans have been evolving for greater intelligence for a very long time now, any free easy gains already been made. You could probably get larger brain volume rather easily with birth by caesarian only, but that doesn’t seem like a good idea to me.
Humans have been evolving for greater intelligence for a very long time now, any free easy gains already been made.
I don’t know. It may or may not be true, but it doesn’t look obvious to me.
The issue is that “evolving for greater intelligence” competes with other things like “evolving for greater strength” or “evolving for greater alpha-ness” or maybe even simply “evolving to survive famines”.
Because of TANSTAAFL greater intelligence comes at a cost (as a trivial example, the human brain consumes a LOT of energy) and the trade-offs the evolution makes are appropriate for the then-current environment. And our current environment is markedly different (there’s your drastic change) from the one in which modern humans actually evolved.
It is quite possible that some trade-offs which held down the growth of intelligence are no longer operational and humans can/will continue to evolve towards even higher IQ.
Practically, of course, the point is moot as evolution is very very slow and humans will self-modify much more rapidly than evolution could provide any noticeable gains.
It is quite possible that some trade-offs which held down the growth of intelligence are no longer operational and humans can/will continue to evolve towards even higher IQ.
Maybe, but as you say, it would come at potential cost. E.g. gain of a few points but you won’t survive famine, that doesn’t sound very good.
Or much more insidiously, gains on an IQ test, at the expense of ability to form/organize/use complex background knowledge (IQ tests are designed to be minimally affected by extra background knowledge).
Practically, of course, the point is moot as evolution is very very slow and humans will self-modify much more rapidly than evolution could provide any noticeable gains.
Yeah, either that, or the civilization goes kaput and it’s back to all-natural selection.
Damage this, damage that, select this bad gene, that bad gene, and you get yourself docile floppy eared dog with the IQ equivalent of severe mental retardation, compared to a wolf.
Many breeds of dogs are certainly very dim compared to wolves, but I’m not so sure that some aren’t just as intelligent, perhaps more so. It can be difficult to evaluate the relative intelligence of dogs and wolves, because some of the hallmarks by which we measure the most intelligent dogs (such as the complexity of tasks they can be trained to perform) do not apply to wolves because they’re so much less cooperative.
Considering the intellectual tasks the smarter breeds of dogs are capable of though, I wouldn’t rule out the possibility of eugenic selection for intelligence relative to wolves, for e.g. border collies, standard poodles and such.
Thing is, of possible mutations within any gene (coding for a protein), vast majority cause loss of it’s original function. This makes the speed of evolution dramatically dependent to the specific details of how the change is accomplished.
Brain volume isn’t necessarily a very good proxy, some animals are significantly smarter than other animals which have larger brains. Rats, for instance, may be more intelligent than some animals which are capable of eating rats, and have much larger brains due to greater body volume.
The vast majority of the difference between dogs and wolves isn’t due to mutation, but selective concentration of genes which already existed within the grey wolf gene pool.
The vast majority of the difference between dogs and wolves isn’t due to mutation, but selective concentration of genes which already existed within the grey wolf gene pool.
As far as I remember, dogs are NOT domesticated wolves. Dogs and wolves have a common ancestor, but they diverged quite a while ago, possibly even before domestication. I vaguely recall that jackals were also somehow involved in dog ancestry.
The common ancestor of dogs and gray wolves, while perhaps having some differences with modern wolves, was still a gray wolf, and this is supported by the paper you linked below. While it’s true that modern gray wolves have less diversity than ancestral ones, what Desrtopa said is also correct.
I think this is incorrect, the most recent source I’ve read on the subject indicated that nearly the entire gene diversity out of all breeds of dogs is just a subset of the gene diversity that already existed in grey wolves.
The success in developing tame silver foxes with only a few generations of selective breeding suggests that domestic traits can be bred into canines without additional mutation just by imposing selection effects to sort for genes already existing within their population.
To identify genetic changes underlying dog domestication and reconstruct their early evolutionary history, we generated high-quality genome sequences from three gray wolves, one from each of the three putative centers of dog domestication, two basal dog lineages (Basenji and Dingo) and a golden jackal as an outgroup. Analysis of these sequences supports a demographic model in which dogs and wolves diverged through a dynamic process involving population bottlenecks in both lineages and post-divergence gene flow. In dogs, the domestication bottleneck involved at least a 16-fold reduction in population size, a much more severe bottleneck than estimated previously. A sharp bottleneck in wolves occurred soon after their divergence from dogs, implying that the pool of diversity from which dogs arose was substantially larger than represented by modern wolf populations. We narrow the plausible range for the date of initial dog domestication to an interval spanning 11–16 thousand years ago, predating the rise of agriculture.
If you truncate less of the tail, it takes more generations to move the mean, but I believe that by the time it moves the same distance, the variance shrinks less.
If you have a randomly mating population, apply assortative mating for a few generations, apply one generation of selection, and let randomly mix, it costs less variance for the same mean as if you don’t do assortative mating. That’s because assortative mating is a kind of selection, so this is like several generations of selection. If you start and end with an equilibrium of assortative mating, I’m not sure what happens. Also, assortative mating increases the variance, so you have to distinguish between the variance of the population and the variance of the population that would result if you switched to random mating.
Assume total heritability, random mating, additive genetics, and a single 50% truncation event. In the first generation, the right tail becomes 4x larger as a proportion of the population, but it gets smaller in equilibrium. The new mean is 0.8 standard deviations above the old mean. The new standard deviation is 0.6 times the old one. When it reaches equilibrium and becomes a Gaussian with those parameters, the crossover where the old population had a thicker tail than the new is about two standard deviations. At three standard deviations, the new distribution is only 1⁄10 of the old distribution. But I don’t know how much time it takes to get there.
Thank you, I’m pretty surprised by that result. Two questions: does assortive mating merely slow down that process? And is there any way to increase the both the average and the standard deviation?
You need new mutations to increase the standard deviation, that takes a lot of time and a big population size.
Also, having a genetic disorder applies larger selection pressure to the other genes.
If we are to think of some real ‘eugenic’ population bottleneck, such as WW2 related, the correlation between intelligence and survival is, frankly, shit, plus a lot of small, geographically co-located sub-populations where a bunch of beneficial genes have been slowly increasing in prevalence get completely wiped out, with loss of all copies of that gene.
Bottom line is, selective breeding of larger corn kernels works quickly because the nature hasn’t been breeding for larger corn kernels to begin with, it has been breeding optimum kernel sizes, and to get large kernels you’re just selecting genetic disorders. There’s nothing that you can wreck about the brain that would turn you into a genius, there’s a plenty of things you can wreck about growth that would make corn kernels big.
Or just some mutagens.
It seems to me that this would work much better for traits that can be accomplished through loss of function (e.g. larger corn kernels, through loss of function of regulator genes) than in general. At too high mutation rate, complex functionality can’t be preserved.
One thing to keep in mind eugenics wise is that pretty much all the breeding methods we employ for other species are dysgenic—we are producing cripples to our own benefit or amusement. Damage this, damage that, select this bad gene, that bad gene, and you get yourself docile floppy eared dog with the IQ equivalent of severe mental retardation, compared to a wolf.
I assume by ‘dysgenic’ you mean ‘less fit than unbred specimens for reproductive fitness in the wild’. (You couldn’t mean ‘reproductive fitness’ in general, given how many dogs there are compared to how many wolves there are now.)
This seems like an odd point to make. Of course we breed animals to be less-reproductively-fit-in-the-wild—if they were already ideal for our multifarous purposes, why would we be explicitly breeding them at all? (If they were already ideal for eating or being pets or whatever, we would simply capture & use them or raise them normally without any interference in their reproduction.)
It’d be a pointless point if there was a symmetry between fitness in the wild and fitness for our purpose. There isn’t—fitness in the wild is very seldom improved by loss-of-function mutations, whereas fitness for our purposes, starting from the species that have been evolving for fitness in the wild, very often is. Rapid success at breeding larger corn kernels is not going to generalize into rapid success at breeding ubermensch.
There’s no reason evolution would have already have optimized for all the intelligence-related alleles; if it had, they would have reached fixation.
I think it is. All the genetic data seems to point to: much of intelligence is genetic, highly polygenic, not fixated, and additive. All of that translates to breedability: we have a lot of easily identified variants present in only parts of the population; hence, breedable.
There’s no question that evolution can continue. The issue is that the rate you can attain for different traits differ. For example, evolving smaller animals from larger animals (by a given factor) is an order of magnitude faster process than evolving larger animals from smaller animals. ( http://news.ucsc.edu/2012/01/body-size.html ). I think you wouldn’t disagree that it would be far quicker to breed a 50 point IQ drop than 50 point IQ rise?
I guess you refer to those studies on intelligence genes which flood the popular media, which tend to have small effect sizes and are of exactly the kind that is very prone to superfluous results.
But what does that have to do with breeding for our objective purpose? It may be easier to destroy functionality than create it, but evolution is creating functionality for living in the wild and doing something like hunting mice while we’re interesting in creating functionality to do something like understand human social cues and trading off against things like aggression and hostility towards the unknown. In both cases, functionality is being created and trading off against something else, and there’s no reason to expect the change for one case to be beneficial for the other. Border collies may be geniuses at memorizing words and herding sheep and both of these feats required intense selection, but both skills are worse than useless for surviving in the wild as a wolf...
The original studies, yes, the ones like candidate-gene studies where n rarely is more than a few hundred, but the ones using proper sample sizes like n>50000 and genome-wide significance level seem trustworthy to me. They seem to be replicating.
Well, my point was that you can’t expect the same rate of advances from some IQ breeding programme that we get when breeding traits arising via loss-of-function mutations.
They don’t seem to be replicating very well...
http://arstechnica.com/science/2014/09/researchers-search-for-genes-behind-intelligence-find-almost-nothing/
Sure, there’s a huge genetic component, but almost none of it is “easily identified”.
Generally you can expect that parameters such as e.g. initial receptor density at a specific kind of synapse would be influenced by multiple genes and have an optimum, where either higher or lower value is sub-optimal. So you can easily get one of the shapes from the bottom row in
http://en.wikipedia.org/wiki/Correlation_and_dependence#/media/File:Correlation_examples2.svg
i.e. little or no correlation between IQ and that parameter (and little or no correlation between IQ and any one of the many genes influencing said parameter).
edit: that is to say, for example if we have an allele which slightly increases number of receptors on a synapse between some neuron type A and some neuron type B, that can either increase or decrease the intelligence depending on whenever the activation of Bs by As would be too low or too high otherwise (as determined by all the other genes). So this allele affects intelligence, sure, but not in a simple easy to detect way.
I am not sure this is generally true.
The wild equivalent to “fitness for our purposes” is a drastic change in the environment which starts to select for different criteria. In such conditions organisms certainly select for new-useful-function mutations, but they also select for loss-of-no-longer-useful-function mutations. Functionality tends to be expensive (e.g. in energy) and if you don’t need it, you’re better off discarding it.
Remnants of lost functionality are common.
Those drastic changes rarely happen, though. In humans, the most recent very well known one was adult lactose tolerance—something that switched lactase off in adulthood no longer does.
edit: and somewhat back to the original point with regards to eugenics—humans have been evolving intelligence for a while already, so selection for intelligence doesn’t seem like a dramatic change.
That, by the way, is an interesting example of both adding functionality (now adults can drink milk!) and losing functionality (the gene which turns off lactase production in adulthood got broken and no longer works in many people).
Yeah. Anyhow, my original point has to do with attempts to breed humans for intelligence. Humans have been evolving for greater intelligence for a very long time now, any free easy gains already been made. You could probably get larger brain volume rather easily with birth by caesarian only, but that doesn’t seem like a good idea to me.
I don’t know. It may or may not be true, but it doesn’t look obvious to me.
The issue is that “evolving for greater intelligence” competes with other things like “evolving for greater strength” or “evolving for greater alpha-ness” or maybe even simply “evolving to survive famines”.
Because of TANSTAAFL greater intelligence comes at a cost (as a trivial example, the human brain consumes a LOT of energy) and the trade-offs the evolution makes are appropriate for the then-current environment. And our current environment is markedly different (there’s your drastic change) from the one in which modern humans actually evolved.
It is quite possible that some trade-offs which held down the growth of intelligence are no longer operational and humans can/will continue to evolve towards even higher IQ.
Practically, of course, the point is moot as evolution is very very slow and humans will self-modify much more rapidly than evolution could provide any noticeable gains.
Maybe, but as you say, it would come at potential cost. E.g. gain of a few points but you won’t survive famine, that doesn’t sound very good.
Or much more insidiously, gains on an IQ test, at the expense of ability to form/organize/use complex background knowledge (IQ tests are designed to be minimally affected by extra background knowledge).
Yeah, either that, or the civilization goes kaput and it’s back to all-natural selection.
Think of this in terms of complexity (use your favorite measure). The point is that evolution has a much easier time reducing it than increasing it.
Many breeds of dogs are certainly very dim compared to wolves, but I’m not so sure that some aren’t just as intelligent, perhaps more so. It can be difficult to evaluate the relative intelligence of dogs and wolves, because some of the hallmarks by which we measure the most intelligent dogs (such as the complexity of tasks they can be trained to perform) do not apply to wolves because they’re so much less cooperative.
Considering the intellectual tasks the smarter breeds of dogs are capable of though, I wouldn’t rule out the possibility of eugenic selection for intelligence relative to wolves, for e.g. border collies, standard poodles and such.
Wolves are under strong selection pressure as well, though.
Intelligence comparisons are of course tricky, but one could compare brain volumes as a proxy, and the comparison is not in favor of dogs.
Thing is, of possible mutations within any gene (coding for a protein), vast majority cause loss of it’s original function. This makes the speed of evolution dramatically dependent to the specific details of how the change is accomplished.
Brain volume isn’t necessarily a very good proxy, some animals are significantly smarter than other animals which have larger brains. Rats, for instance, may be more intelligent than some animals which are capable of eating rats, and have much larger brains due to greater body volume.
The vast majority of the difference between dogs and wolves isn’t due to mutation, but selective concentration of genes which already existed within the grey wolf gene pool.
As far as I remember, dogs are NOT domesticated wolves. Dogs and wolves have a common ancestor, but they diverged quite a while ago, possibly even before domestication. I vaguely recall that jackals were also somehow involved in dog ancestry.
The common ancestor of dogs and gray wolves, while perhaps having some differences with modern wolves, was still a gray wolf, and this is supported by the paper you linked below. While it’s true that modern gray wolves have less diversity than ancestral ones, what Desrtopa said is also correct.
I think this is incorrect, the most recent source I’ve read on the subject indicated that nearly the entire gene diversity out of all breeds of dogs is just a subset of the gene diversity that already existed in grey wolves.
WIkipedia also supports the contention that dogs are extracted directly from grey wolves a few tens of thousands of years ago, too recently for them to have diverged from some meaningfully distinct common ancestor.
The success in developing tame silver foxes with only a few generations of selective breeding suggests that domestic traits can be bred into canines without additional mutation just by imposing selection effects to sort for genes already existing within their population.
This claims otherwise. Notably:
To identify genetic changes underlying dog domestication and reconstruct their early evolutionary history, we generated high-quality genome sequences from three gray wolves, one from each of the three putative centers of dog domestication, two basal dog lineages (Basenji and Dingo) and a golden jackal as an outgroup. Analysis of these sequences supports a demographic model in which dogs and wolves diverged through a dynamic process involving population bottlenecks in both lineages and post-divergence gene flow. In dogs, the domestication bottleneck involved at least a 16-fold reduction in population size, a much more severe bottleneck than estimated previously. A sharp bottleneck in wolves occurred soon after their divergence from dogs, implying that the pool of diversity from which dogs arose was substantially larger than represented by modern wolf populations. We narrow the plausible range for the date of initial dog domestication to an interval spanning 11–16 thousand years ago, predating the rise of agriculture.
If you truncate less of the tail, it takes more generations to move the mean, but I believe that by the time it moves the same distance, the variance shrinks less.
If you have a randomly mating population, apply assortative mating for a few generations, apply one generation of selection, and let randomly mix, it costs less variance for the same mean as if you don’t do assortative mating. That’s because assortative mating is a kind of selection, so this is like several generations of selection. If you start and end with an equilibrium of assortative mating, I’m not sure what happens. Also, assortative mating increases the variance, so you have to distinguish between the variance of the population and the variance of the population that would result if you switched to random mating.
test