Complex sentence: He thought Adam and Eve were Caucasian and that was the original race of mankind, and the other two races arose by survivors' escaping in different directions after a major catastrophe hit the earth 5,000 years ago.
Split into simpler sentences: He thought Adam and Eve were Caucasian and hence the original race of mankind. The other two races arose by survivors' escaping in different directions after a major catastrophe hit the earth 5,000 years ago.