Board Thread:General Discussion/@comment-2.222.5.48-20160522233350/@comment-26247132-20160522234759

The prevailing fan theory is because of genetic engineering. It comes from a throwaway line Clarke said in Coup de Grace about Sky People's blood being genetically engineered. It also might help explain why they heal so fast and never seem to need to sleep or eat but it's never been confirmed either way in the show.