I want to know the answer to the following question:
What are probably the primary forces of nature which shaped human races?
All the background I'm provided with is that "Forensic physical anthropologist and professor George W. Gill has said that the idea that race is only skin deep "is simply not true, as any experienced forensic anthropologist will affirm" and "Many morphological features tend to follow geographic boundaries coinciding often with climatic zones.". Is that enough to answer the question?