1.) Ancient Alien hybridization hypothesis. Travellers from another world show up in our early history. The travellers cannot return home, & they are dying. The only way to survive is too pass their genetics down the generations through breeding into the native species. 2.) But this does not work, they are too different a species to mix. The travellers could live for thousands of years, so they had time to solve this problem. They used their knowledge of genetic engineering to make a hybrid human.