Question:
agree the increased mixing of current human genes due to increased mobility due to intelligence reduces chance of a new species by OLD selection methods. It appears that people tend to marry, and hence breed, with others like themselves. thus greater mobility will allow more like people to find each other. It may be that the effect of greater mobility will be to polarise the phenotypes and hence genotypes of people. then two races will develop, possibly one short, dark, "Celtic" and the other tall, fair, "Nordic"; A new species arrives when they stop interbreeding Fred Dowson (UK) Semper in Stercum sumus: solum profundus variat.

Answer: I was under the impression that a new species emurges as interbreedingis largely precluded by increasing genetic incompatabilities thatprevent offspring or render them reproductivly unviable.

I say largely precluded because it is always imaginable that ocasionalinterbreeding could be possible for time provideing a grey area asseperate variaties of a species evolve and or drift to less and lessbiological compatablity. Pruducts of that interbreeding would thenpresumabily not propagate far in either popultion untill compatabilitytheory took over and completely severed the link.

It's possible with the propagation factor that species seperation couldin a sense happen before interbreeding is precluded.While that contradicts the usual definition of a species it isimaginable that two inter beeeing "varieties" could regularly producereproductivly capable offspring but that they would have extreemlydiminished chances of survival for some complex reason. Flowers withvery specific polination requirements in very constrained environmentscome to mind.

In any case I strongly suspect that species boundries are notqualititaivly different from variation within species for purposes ofinterbreeding or other large scale holistic fitness factors.I would contend rather gradual decline as difference accrues.Case in point. Chimp and human sperm which can (unlike more distantspecies) enter each other's eggs but are then infertile.

Perhaps not so long ago they could inter mingle and produse offspringwhich were not viable in either community. Eventually biology wouldgive up the option all together.