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I first saw this concept in the context of intelligence in "The Bell Curve" by Richard J. Herrnstein and Charles Murray (1996). They suggested the process is a

I first saw this concept in the context of intelligence in "The Bell Curve" by Richard J. Herrnstein and Charles Murray (1996). They suggested the process is accelerating dramatically with development of situations that make it easier for intelligent people to find each other: the movement of the population from the farm to cities, higher education, improved communications and less restricted travel. I would not be surprised if online dating sites are also playing a role. Once you start thinking about this in the context of genetics, matings and the potential for a survival advantage and increased quality of life leading to further segregation you wonder if this does not have the potential to eventually result in the development of a new species?! I would be interesting to know if the IQ "density" is significantly altered in certain communities in northern California, Boston, NY, etc. associated with industries selecting for high IQ workers. [Edit]Just amused myself thinking of the Silicon Valley crew as participants in a breeding experiment.

gliese1337 12y ago
Having now learned the terminology, assortative mating could indeed lead to speciation in the general case; it's just a special case of sexual selection. I find it highly unlikely that that will happen with human intelligence, though (despite the fact that it's been used in fiction more than once). The reason is that there's a limit to how big the variance can get- it doesn't grow forever, it grows until limited by other factors (i.e., there are only so many intelligence-promoting alleles that you can possibly have). It would take intentional segregation to cut off all gene flow between the upper and lower halves of the intelligence Bell curve, thus allowing other differences to pile up between the populations, to cause speciation. And as noted elsethread, that's called eugenics and generally frowned upon in polite society.
- sfbsfbsfb 12y ago
  Interestingly, the current mating and segregation trends, to the extent they exist, appear to be completely "natural" and lacking in premeditation. Can't help but wonder if modern humans are not the result of a process that left the Neanderthals ( pre-modern humans, whoever they were) behind. I'm no expert, but I don't think a complete lack of gene flow between groups is thought to be required for the process of speciation.
  - eru 12y ago
    Neanderthals at least had bigger brains than modern humans.
- clarkm 12y ago
  > The reason is that there's a limit to how big the variance can get- it doesn't grow forever, it grows until limited by other factors (i.e., there are only so many intelligence-promoting alleles that you can possibly have). What makes you think that? You could say the same thing about seed size in plants, but comparing modern corn kernels to wild type seeds provides a clear counterexample. You should look at the type of stuff they've done in plants and animals. Here's a paper on the selective breeding of fruit flies for flight speed. The results are astounding: "The mean apparent flying speed of both lines increased from approximately 2 to 170 cm/sec and continued to respond at diminishing rates, without reaching a plateau, for 100 generations. Competitive fitness tests in generations 50 and 85 showed minimal or no fitness loss in selected lines compared to controls." http://www.ncbi.nlm.nih.gov/pubmed/8878686 http://www.ncbi.nlm.nih.gov/pubmed/8878686
jacquesm 12y ago
Species are not 'developed'. They come into being because of isolation and sufficient time passing. Even all the breeding done with dogs has not resulted in speciation. The time scales are vast and the degree of separation that a barrier such as 'intelligence' (for whatever definition you wish to employ) will provide will be insufficient to cause this to happen. No Elois and Morlocks in our future through that avenue. Think about it: if geographic separation and very long spans of time have not been enough then why would a mere trait be enough, we have plenty of examples of the former.
- sfbsfbsfb 12y ago
  It does not seem hard for me to contemplate the possibility that modern humans are primarily defined by our intelligence and that our closest relatives had less of it. Of course, as you point out, these developments occur over the course of perhaps hundreds of thousands of generations.It also seems pretty clear that catastrophes that dramatically reduce population sizes may also play a significant role in the process. Survivors of a catastrophe are likely to be geographically localized. The catastrophe eliminates gene pools and, by chance, selects for small subsets of the previously existing pool. Wash, rinse, repeat. And in a cosmic heartbeat....you have something different than what you started with.
  - jacquesm 12y ago
    Such catastrophes would have to do a better job of isolating people than they've been doing so far. Humanity is remarkably similar from a genetic perspective when taken as a species. I don't think your theory stands much chance unless you're willing to go interplanetary or inter-stellar. On planet earth we are remarkably mobile, to the point where if we lose all shipping ability and even knowledge of other civilizations that we'll likely re-discover all this from first principles within at most a few thousand years.
    - sfbsfbsfb 12y ago
      I was thinking "catastrophe" as in a wipe out the dinosaurs asteroid hit or a global pandemic that takes out 95% of the population (think Ebola)or an EMP event that results civilization collapse, etc. So if Silicon Valley residents are the only survivors (god help us :-)and there is a higher IQ density there than other locations and if IQ is really significantly genetic, then the average IQ of humans has increased and can be maintained in the population. Other pockets of survivors would have an IQ density similar to that present in the general population existing before the catastrophe and based on our hypothetical case, lower than that in Silicon Valley. It is the geographic isolation and geographic concentration of a particular genetic trait that makes this type of selection possible.

gliese1337 12y ago

Having now learned the terminology, assortative mating could indeed lead to speciation in the general case; it's just a special case of sexual selection. I find it highly unlikely that that will happen with human intelligence, though (despite the fact that it's been used in fiction more than once). The reason is that there's a limit to how big the variance can get- it doesn't grow forever, it grows until limited by other factors (i.e., there are only so many intelligence-promoting alleles that you can possibly have). It would take intentional segregation to cut off all gene flow between the upper and lower halves of the intelligence Bell curve, thus allowing other differences to pile up between the populations, to cause speciation. And as noted elsethread, that's called eugenics and generally frowned upon in polite society.

sfbsfbsfb 12y ago
Interestingly, the current mating and segregation trends, to the extent they exist, appear to be completely "natural" and lacking in premeditation. Can't help but wonder if modern humans are not the result of a process that left the Neanderthals ( pre-modern humans, whoever they were) behind. I'm no expert, but I don't think a complete lack of gene flow between groups is thought to be required for the process of speciation.
- eru 12y ago
  Neanderthals at least had bigger brains than modern humans.
clarkm 12y ago
> The reason is that there's a limit to how big the variance can get- it doesn't grow forever, it grows until limited by other factors (i.e., there are only so many intelligence-promoting alleles that you can possibly have). What makes you think that? You could say the same thing about seed size in plants, but comparing modern corn kernels to wild type seeds provides a clear counterexample. You should look at the type of stuff they've done in plants and animals. Here's a paper on the selective breeding of fruit flies for flight speed. The results are astounding: "The mean apparent flying speed of both lines increased from approximately 2 to 170 cm/sec and continued to respond at diminishing rates, without reaching a plateau, for 100 generations. Competitive fitness tests in generations 50 and 85 showed minimal or no fitness loss in selected lines compared to controls." http://www.ncbi.nlm.nih.gov/pubmed/8878686 http://www.ncbi.nlm.nih.gov/pubmed/8878686

jacquesm 12y ago

Species are not 'developed'. They come into being because of isolation and sufficient time passing. Even all the breeding done with dogs has not resulted in speciation. The time scales are vast and the degree of separation that a barrier such as 'intelligence' (for whatever definition you wish to employ) will provide will be insufficient to cause this to happen. No Elois and Morlocks in our future through that avenue. Think about it: if geographic separation and very long spans of time have not been enough then why would a mere trait be enough, we have plenty of examples of the former.

sfbsfbsfb 12y ago
It does not seem hard for me to contemplate the possibility that modern humans are primarily defined by our intelligence and that our closest relatives had less of it. Of course, as you point out, these developments occur over the course of perhaps hundreds of thousands of generations.It also seems pretty clear that catastrophes that dramatically reduce population sizes may also play a significant role in the process. Survivors of a catastrophe are likely to be geographically localized. The catastrophe eliminates gene pools and, by chance, selects for small subsets of the previously existing pool. Wash, rinse, repeat. And in a cosmic heartbeat....you have something different than what you started with.
- jacquesm 12y ago
  Such catastrophes would have to do a better job of isolating people than they've been doing so far. Humanity is remarkably similar from a genetic perspective when taken as a species. I don't think your theory stands much chance unless you're willing to go interplanetary or inter-stellar. On planet earth we are remarkably mobile, to the point where if we lose all shipping ability and even knowledge of other civilizations that we'll likely re-discover all this from first principles within at most a few thousand years.
  - sfbsfbsfb 12y ago
    I was thinking "catastrophe" as in a wipe out the dinosaurs asteroid hit or a global pandemic that takes out 95% of the population (think Ebola)or an EMP event that results civilization collapse, etc. So if Silicon Valley residents are the only survivors (god help us :-)and there is a higher IQ density there than other locations and if IQ is really significantly genetic, then the average IQ of humans has increased and can be maintained in the population. Other pockets of survivors would have an IQ density similar to that present in the general population existing before the catastrophe and based on our hypothetical case, lower than that in Silicon Valley. It is the geographic isolation and geographic concentration of a particular genetic trait that makes this type of selection possible.