This helps prove my point. If all you consider is genetics in determining cultural ability, your findings will not reflect reality. Genetics alone do not determine cultural ability. The mixing of the races has not caused this supposed degeneration of society. It is the sins of mankind, our turning away from God, that has caused so much misery, in addition to other reasons.
Not really. The Romans and Germanic tribes were not genetically far off compared to say Africans or Arabs to Romans. The Germanic tribes brought down the Roman Empire since Rome was past its glory days and was inferior in some respects compared to say the days of Augustus.
The idea is that if genetics alone determined cultural ability, and if the Germanic people are genetically superior, then history would different. There would have been a German Empire, not a Roman Empire. Culture is not based on genetics, but on many factors, including availability of resources, climate, other cultural forces, etc.
Let's say you had three exact copies of one man, and placed each one in different areas. One would get a location with an abundance of resources, another with some, and another with few. Even though the men are the same, their lives would differ.