[sfbsfbsfb]

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.

[jacquesm]

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.

[perrylaj]

It's certainly possible if you factor in the social and geographic trends and take them to extreme conclusions. It's merely reproductive separation that is required. Whether this be due to geography, climate, mating calls or unattractive IQ isn't really of import. I'll agree that right now the barrier isn't sufficient enough, but I don't think that is what OP was saying (could be wrong).

That said, your point about the time scales is definitely on mark. It would take a long time and likely far more significant isolation than present (don't have numbers). Genetic engineering could speed that up substantially.

Of course social factors would likely prohibit any talk about separate species. From a pure biologist perspective there are many different animal species fully capable of reproducing but are speciated because their natural breeding behavior (or location) doesn't support interbreeding. Using the same measure/definition, one could objectively argue that uncontacted tribes and isolated peoples are a different 'species'.

I personally think scientists need to agree on some fundamental genetic/epigenetic (maybe even microbiomic) markers of speciation and move away from more subjective definitions. Reproductive potential makes sense when looking at speciation likelihood, but I am not sure it makes sense as a definition of different species.

[jacquesm]

Being able to interbreed is the very definition of a species.

So if two specimen are capable of breeding and the resulting offspring is not sterile they are considered to be of the same species.

Being from an un-contacted tribe has nothing whatsoever to do with speciation.

[perrylaj]

That's actually not the definition used in biology. Simple example: The entire genus Amphiprion (aka anemonefish) are speciated due to appearance and regional locality. They can and do interbreed when introduced into each others populations, and have fertile offspring that are mixed species. They are declared species due to their appearance, and their natural range's prevention of interbreeding. That said, there are areas where some ranges overlap and it's not uncommon that one species mates with another and has hybrid offspring.

Being genetically capable of interbreeding makes sense as a definition of speciation, but that is not how species are currently identified. Natural range, aesthetics, and more than that, whether or not they DO interbreed in the wild (vs physically/genetically capable) play a more significant role in determining species.

There are many 'hybrid' species in nature, which is what I feel warrants some revision, perhaps using genetic data to restructure many classifications as subspecies rather than independent species.

edit: Sorry, I think I may have misinterpreted what you said to some extent and think we generally agree. I will maintain that according to the classification methods described, people such as the Sentinelese, may well be considered a separate species to an unbiased observer using the same guidelines we apply to other animals due to slightly different physical characteristics and social/geographical reproductive isolation prevents the possibility of breeding with anyone outside of their group.

[yummyfajitas]

Being able to interbreed is the very definition of a species.

It isn't, and cannot be. The relation A interbreeds with B is not transitive.

Larus Gulls originated in Finland and spread west, evolving as they moved. Eventually some of them reached England. The Finnish ones breed with the Russian ones, Russian with Canadian, Canadian with English, but the English don't breed with the Finnish.

http://en.wikipedia.org/wiki/Ring_species

[jacquesm]

Sure. And that's just the spatial variety. There is also the temporal variety of that same phenomenon.

If a 3 million year old ancestor would suddenly pop out of nowhere into our midst chances are that we're far enough removed for interbreeding to be impossible and yet, we were able to breed at every intermediary stage just fine.

But for all normal everyday intents and purposes that definition holds up just fine. It's when you start to zoom in on what a species really is that it becomes more nebulous until you realize that all there is is individuals and their breeding capabilities.

Species are a phenomenon that is observed rather than one that actually exists.

Fascinating stuff.

[sfbsfbsfb]

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]

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]

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.

[jacquesm]

What makes you feel that the average IQ of Silicon Valley might be higher than say Beijing, Tokyo, Adelaide or Moscow?

[sfbsfbsfb]

Nothing. I was just using an example of which I had some familiarity. In the context of this hypothetical thread, it is interesting to note that there is apparently some scientific data suggesting that Asians have a slightly higher IQ than other races. Not being an expert I can't readily provide the references. The other reason for using Silicon Valley as an example is that the theoretical we are discussing requires a survivor population that has a higher IQ density than the average population. The larger the sampling the closer the IQ density approaches average. Although I guess the argument would still hold for a city or country. I was just thinking that the difference in IQ density between Silicon Vally and California as a whole might be 20 points while the difference between China and the US might be 2 points.

[ap22213]

Unfortunately for us, it seems that the more 'evolved' we get, the smaller our brains get:

http://www.npr.org/2011/01/02/132591244/our-brains-are-shrin...

[gliese1337]

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.

[clarkm]

> 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

[sfbsfbsfb]

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]

Neanderthals at least had bigger brains than modern humans.