pushmedia1, 
 
You guys are making this much more complicated than it really is. China has been a united cultural unit for thousands of years, they have never had any inclination towards expansion, they have always looked inwards. 
 
On top of this, they have very little genetic diversity. They all think alike. How else could their government get 86% approval ratings in independant surveys? 
 
On the other hand, the west consisted of diverse groups and warring factions who, because of their military needs, discovered vast resources and put them to effective use. What reason would China have for doing anything like this? Read the history of China sometime, it is a snoozefest compared to western history. 
 
The real explanations are simple, more complex theories are just myth-making by experts who need to justify their expertise.

While economics may seem to be the critical factor, I think the economic developments were merely a side effect of the massive culture gap between Europe and Asia. The seafaring European nations developed an aggressive, exploratory, expansionistic culture. The Asian cultures did not. This explains their eventual economic and military dominance. All it took was Spain uniting under one ruler to break off the years of infighting and turn that aggression on the rest of the world. Other countries followed suit and eventually Portugal, England, France, and the Netherlands were all full participants in the new style of exploratory empire-building. No Asian power has ever gone through this type of cultural phase (Japan probably comes closest). Basically China has always been happy with it's own piece of land and has never felt the same kind of drive.

I wonder how the same biometrics of the average American woman have changed in the same time period?

Your post is fascinating! The Alans weren't the only long-distance travelers in ancient times: numerous other Germanic tribes, the Celts, the Mongols and the Polynesians all moved entire segments of their populations (not just warrior elites, but entire tribes and families). I think we often underestimate the great degree of travel and migration which has always been done by humans.

What worries me about genetic engineering is the possible side effects. For instance, there is evidence that creativity and mental illness are closely related, and great mathematical ability may be associated with an increased risk of autism. Since very little is known about the genes involved in intelligence, creating designer babies might have a whole slew of nasty surprises. 
 
In fact, the example of breeding dogs offers an excellent example of the perils of selective breeding: herding dogs often have obsessive-compulsive problems, which makes them good at herding sheep but also makes them lick or chew themselves raw (especially when they're kept as house pets). I think anyone advocating designer babies is being irresponsible given our current level of knowledge.